Wikipedia - User contributions [en]

User talk:JSpudeman/archive03

2007-01-21T19:11:40Z

JSpudeman: ←Created page with ' == Hello == There's been a stay of execution. :) I'll be sticking around for a bit. Yeah as for calling me a girl, I have no idea. I thought I'd made it clear on m...'

== Hello ==
There's been a stay of execution. :) I'll be sticking around for a bit. Yeah as for calling me a girl, I have no idea. I thought I'd made it clear on my page but now I just added the line "I am male". But that probably still won't fix it. They see "kitty" and assume female. Why I don't know. *shrug* Btw, the "This page is too long" thing is just a warning. I've seen talk pages over 200K. I usually archive around 70K...don't think I'm there yet. Take care. --[[User:Woohookitty|''Woohookitty'']][[User talk:Woohookitty|(cat scratches)]] 16:23, 11 January 2006 (UTC)

:[[Wikipedia:WikiProject Medicine]]. There you go. :) And it looks like it's a very active Wikiproject. Some of them aren't but that one is. I'd post your concerns on the talk page and go from there. They'll give you some input or lead you to the right place to go. --[[User:Woohookitty|''Woohookitty'']][[User talk:Woohookitty|(cat scratches)]] 16:50, 11 January 2006 (UTC)

== Re: Hello! ==

Hello, Spum, it's nice to meet you. I'm always happy to see other health-care workers and friends contributing to Wikipedia. I see you've been around for a while, but if you need anything, please don't hesitate to ask. Also, you depending on what your areas of interest are, you may find [[Wikipedia:WikiProject Preclinical Medicine]], [[WP:CLINMED|Clinical medicine]], [[WP:MED|Medicine]], or the [[WP:MCOTW|Medicine Collaboration of the Week]] interesting. Good luck with your training! — [[User:Knowledge Seeker|Knowledge Seeker]] [[User talk:Knowledge Seeker|দ]] 19:03, 12 January 2006 (UTC)
:I wonder, too, if you'd considered removing the information about scientology from your user page. While I am not particularly a fan of scientology myself, I'm not certain that this user box will have its desired effect, and some would consider it to be in poor taste. Perhaps you'd consider writing about why you don't like it on your user page instead. Just a thought! — [[User:Knowledge Seeker|Knowledge Seeker]] [[User talk:Knowledge Seeker|দ]] 19:22, 12 January 2006 (UTC)

== business under the guise of a religion ==

Categories/templates/userboxes/etc that say, "I am against X," where "X" is not related to the task making Wikipedia.....well, I just do not understand how these help the project. In fact, they seem to damage the project by distracting Wikipedians from work on the encyclopedia. --[[User:JWSchmidt|JWSchmidt]] 21:33, 12 January 2006 (UTC)
:do user pages distract from work on the encyclopedia? I'm very interested in the health of the community of editors who are constructing Wikipedia. I think that user pages can play a useful role in allowing Wikipedians to express their thoughts and concerns. This can be healthy in that it allows us all to participate in a process by which we can think critically about issues and express our views and it provides a mechanism by which the community members have a chance to better understand each other. "Generally, you should avoid substantial content on your user page that is unrelated to Wikipedia" and "Wikipedian categories are intended to help Wikipedians with similar broad interests to congregate and converse" need to be in balance. In my case, I might declare my "broad interest" in biology and willingness to help develop Wikipedia articles related to science. I have specific interests such as concern about attempts to insert specific religious ideas into public school science classes, but I do not think it would be constructive to have a category called "Wikipedians against creationism". There has to be cooperation between scientists and creationists to make good Wikipedia articles about creationism and topics like evolution. Such cooperation is easier if an atmosphere of attack and animosity is not created within Wikipedia. --[[User:JWSchmidt|JWSchmidt]] 22:08, 12 January 2006 (UTC)

==Re: tables lining up on Main Page Redesign Draft ==

I'm not sure exactly what element you are talking about. I think the bottoms of the columns line up. Do they line up on your browser?

If you are referring to the second headings ("On this day" and "Did you know"), it wasn't clear in your post. I'm not sure how to make those line up, but I can work on it, if that is what you were referring to. I've updated the news items, and the second-headings currently do not line-up. Take a look. And thank you for the feedback and words of encouragement. [[User:Go for it!|Go for it!]] 22:05, 12 January 2006 (UTC)

==Okay, how's this?==

[[User:Go for it!/Workshop/Main Page Redesign Draft 6]] --[[User:Go for it!|Go for it!]] 22:47, 12 January 2006 (UTC)

== Heyyyyyyy ==

.... thanks for the Fonzies! Hope your weekend was all chrome and whitewalls. BTW, as a dietician, what do you think of [[Weight Watchers]]? [[User:Katefan0|'''Katefan0''']][[User talk:Katefan0|(scribble)]]/[[User:Katefan0/Poll|mrp]] 08:00, 16 January 2006 (UTC)

== Let's get busy ==

Hello there spum, it's me, your other User ;-) How's tricks my friend? [[User:Sforzando|Sforzando]] 11:58, 16 January 2006 (UTC)

==Expand==
FYI...expansion requests go on the talk page. See [[Wikipedia:Requests for expansion]] and [[Wikipedia:Template_messages/Talk_namespace#Expansion_requests]]. I've made this mistake a number of times. —[[User:Viriditas|Viriditas]] | [[User talk:Viriditas|Talk]] 14:22, 17 January 2006 (UTC)

== Need your expertise! ==

Hi, i recently made a wikiNews football portal [http://en.wikinews.org/Portal:Football here] and i was wondering if you'd be able to use your design magic and make it look ever more sexier? thanks ever so much! [[User:Spum|The magical Spum-dandy]] 12:20, 17 January 2006 (UTC)

I'd be glad to take a look. BTW, I noticed on your football portal at wikinews that you've used a background on there. What a coincidence! I need the help of someone who knows how to work with backgrounds on Wikipedia pages. See next message. --[[User:Go for it!|Go for it!]] 14:56, 17 January 2006 (UTC)

== How do you create and use backgrounds in Wikipedia? ==

<center>[[Image:Wikipedia-logo.png|165px]]</center>

Welcome to [[Wikipedia]], the free encyclopedia that [[Wikipedia:Introduction|anyone can edit]].


In this English version, started in 2001, we are currently working on [[Special:Statistics|{{NUMBEROFARTICLES}}]] articles.



[[Portal:Art|Art]] | [[Portal:Culture|Culture]] | [[Portal:Geography|Geography]] | [[Portal:Health|Health]] | [[Portal:History|History]] | [[Portal:Biography|People]] | [[Portal:Philosophy|Philosophy]] | [[Portal:Science|Science]] | [[Portal:Society|Society]] | [[Portal:Technology|Technology]]
 ''[[Wikipedia Almanac|Almanac]] · [[Wikipedia:Browse|Categories]] · [[List of glossaries|Glossaries]] · [[List of topic lists|Lists]] · [[Wikipedia:Browse by overview|Overviews]] · [[Portal:Browse|Portals]] · [[Special:Search|Search]] · [[Wikipedia:Questions|Questions]] · [[Wikipedia:News|Site news]] · [[Wikipedia:Quick index|Index]]''

'''''I was wondering if you knew how to:'''''
#Fade the puzzle globe so that it can be placed in the background.
#Place the puzzle globe behind the 4 lines of text of the header.
#Adjust the fading, in case its symbols interfere with the letters of the header.
#Anchor the background, so that it is always behind the header.

This is part of the [[Wikipedia:WikiProject Usability/Main_Page/Draft|Main Page Redesign]] effort, which is now in an '''''open editing session''''' to prepare the next draft for the new voting round which is coming up this Saturday (Jan 21). Check it out!

Any help/guidance you can provide on the background design issue presented above would be most appreciated. --[[User:Go for it!|Go for it!]] 14:56, 17 January 2006 (UTC)

== I used an external stylesheet ==

Pretty simple really. I just used [http://en.wikinews.org/wiki/Portal:Football/football.css Portal:Football/football.css], then used a DIV class, so that then it would link to the actual stylesheet. You can do it on your own userpage as well :-) Gotta get an admin to protect it ;-) [[User:Spum|The magical Spum-dandy]] 15:54, 17 January 2006 (UTC)
:Spum, I just wanted to let you know that I like what you've done with football.css. It looks great. --—[[User:Viriditas|Viriditas]] | [[User talk:Viriditas|Talk]] 09:56, 18 January 2006 (UTC)
I followed your instructions exactly and copied the code from Portal:football and Portal:football/football.css to User:Go for it! and User:Go for it!/Go for it!.css, and it didn't work. Which means I must not have understood your directions. How do you get the program to recognize the .css file and use it for rendering the page? --[[User:Go for it!|Go for it!]] 19:18, 17 January 2006 (UTC)

== [[Lord Voldemort]] ==

That was part of the problem. If it were about something concrete or real, then maybe a basis could be formed based on sources. I'm not criticising the article (which, for the most part, is extremely good), just this one sentence that seems highly speculative at best. There are a lot of bad guys in children's literature, and there's no objective way of telling which is more powerful/evil/seductive/etc. This means that the only resource we have to fall back on are notable sources, such as book review sites. My only concern is that it's using one of the so-called [[WP:WEASEL|weasel words]], which, while not bad in itself, isn't backed up by any kind of sources or references. [[User:Jamyskis|Jamyskis]] [[User_talk:Jamyskis|Whisper]], [[Special:Contributions/Jamyskis|Contribs]] [[Image:Flag_of_Germany.svg|25px|Germany]] 15:47, 18 January 2006 (UTC)

==Would you mind proofreading something for me?==

I'm thinking about requesting adminship, and have written a [[User:Go for it!/Request for adminship draft|draft of my request]]. I would appreciate it if you would proofread it for me, and let me know what you think on its talk page. Thank you. Sincerely, --[[User:Go for it!|Go for it!]] 23:57, 18 January 2006 (UTC)

== Username change ==

Your request has been fulfilled. Regards — [[User:Rdsmith4|Dan]] | [[User talk:Rdsmith4|talk]] 00:18, 24 January 2006 (UTC)

== Portal redesign ==

There seems to be general agreement among the participants of [[Wikipedia:WikiProject Usability]] that after the main page makeover is complete, we will move on to help with portal design. However, we will most likely be taking a top-down approach; we will start with the portals that are listed in the (new)main page's portal section. You're welcome to join, if you like. It's an open community. [[User:Kevin_baas|Kevin Baas]][[User_talk:Kevin_baas|talk]] 22:24, 28 January 2006 (UTC)

==[[Healthy eating]]==
I know the talk page has been quiet for a couple months, but I'm still concerned about this page, and based on your comments I believe you are too. I agree with you that it should be merged into [[Healthy diet]], and I'm also concerned about this page because I feel it has a serious NPOV problem, particularly in the Toxins section. How do you think we should go about fixing this page? Thanks in advance for your help! [[User:EWS23|EWS23]] | [[User talk:EWS23|(Leave me a message!)]] 06:38, 29 January 2006 (UTC)

== Moving pages to wikisource ==
Basically, what you want to do is to use what we call [[Transwiki]]. Basically, you want to create the article in wikisource as Transwiki:X with X being the article name (though if it's more appropriate, you can make the name more specific). And then add it to [[Transwiki#Moved_to_en.wikisource.org|this page]] using the format listed. Since you aren't moving an entire article, In that list, I would mark the article as the name and then in () what you removed. Otherwise, someone might delete the whole article and you don't want that. That should be all you have to do. --[[User:Woohookitty|''Woohookitty'']][[User talk:Woohookitty|(cat scratches)]] 14:18, 16 February 2006 (UTC)

==Image Tagging [[:Image:Pater with susan and charlie.jpg]]==

{| align="CENTER" style="background-color:#FFFFFF; border:8px solid #FF0000; padding:5px;"
|-
|[[Image:Nuvola apps important.svg|30px|Warning sign]]
| <center><big>This media may be '''deleted'''.</big>
</center>
|}

Thanks for uploading '''[[:Image:Pater with susan and charlie.jpg]]'''. I notice the 'image' page currently doesn't specify who created the content, so the [[copyright]] status is therefore unclear. If you have not created this media yourself then you need to argue that we have the right to use the media on Wikipedia (see copyright tagging below). If you have not created the media yourself then you should also specify where you found it, i.e., in most cases link to the website where you got it, and the terms of use for content from that page.

If the media also doesn't have a copyright tag then you must also add one. If you created/took the picture, audio, or video then you can use {{tl|GFDL-self}} to release it under the [[GFDL]]. If you believe the media qualifies as fair use, please read [[Wikipedia:Fair use|fair use]], and then use a tag such as {{tlp|fairusein|article name}} or one of the other tags listed at [[Wikipedia:Image copyright tags#Fair_use]]. See [[Wikipedia:Image copyright tags]] for the full list of copyright tags that you can use.

If you have uploaded other media, please check that you have specified their source and copyright tagged them, too. You can find a list of 'image' pages you have edited by clicking on the "[[Special:Contributions/{{PAGENAME}}|my contributions]]" link (it is located at the very top of any Wikipedia page when you are logged in), and then selecting "Image" from the dropdown box. Note that any unsourced and untagged images will be deleted one week after they have been uploaded, as described on [[wikipedia:Criteria for speedy deletion#Images.2FMedia|criteria for speedy deletion]]. Thank you. [[User:Arniep|Arniep]] 02:09, 20 February 2006 (UTC)

== Say ==
Did you get the stuff moved to Wikisource ok? I never heard back from ya. If not, let me know if you have any questions. --[[User:Woohookitty|''Woohookitty'']][[User talk:Woohookitty|(cat scratches)]] 12:08, 24 February 2006 (UTC)

== [[:Image:Brentoggmonstercamera.jpg]] ==

Hi - If you took this image from a DVD as stated, it is '''not''' in the public domain. Please use an appropriate tag such as {{tl|fairusein}} if you are claiming fair use. Thanks! -[[User:SCEhardt|SCEhard]][[User talk:SCEhardt|T]] 23:46, 11 March 2006 (UTC)

== Chobits — sexual intercourse ==

In the manga, Freya ''specifically'' explains to Hideki that Chi can '''''not''''' have sex, because her reset switch is, well, in her vagina, to be explicit. If Hideki were to make love to Chi, she would be reset, losing all of her memories and reverting to a blank-slate. Normal persocoms can have sex, and in fact in the manga Hideki's boss says, not so subtly, that he uses his for this purpose. ("She makes a good lap-top, if you know what I mean!")[[User:PiccoloNamek|PiccoloNamek]] 18:27, 12 March 2006 (UTC)

Even in the anime, her reset button is never actually touched, because doing so would have resulted in a reset. During the two previous times where somebody came close, she punished them with her shock wave. Remember when Hideki pressed her button for the first time, it made a loud "Clunk" sound. That never happened during the other incidendts. Interestingly, in the anime, after Hideki says that he loves Chi, she has some kind of spasm and sets off her own switch. (You can clearly hear the "clunk" sound.) Perhaps after she finds the person just for her, some kind of parameter is changed, or perhaps after that person is found the switch needs to be pressed to begin the program. But that is just speculation and has no place on Wikipedia.[[User:PiccoloNamek|PiccoloNamek]] 09:15, 13 March 2006 (UTC)

== Mentor ==

Are you willing to be the active mentor for [[user:JarlaxleArtemis]]? Linuxbeak has indicated he is too busy with other matters, and Cool Cat removed himself from the case. JarlaxleArtemis has been causing problems, and has been extremely sluggish about completing his requirements. Without an active mentor he will have to be blocked. -23:11, 23 March 2006 (UTC)

:It's easy to be a cop in a town where everyone obeys the law. ;) (though for some reason that doesn't keep edit wars away from ''[[The Andy Griffith Show]]''.) -[[User:Will Beback|Will Beback]] 10:10, 24 March 2006 (UTC)

== Body Mass Index ==

Well, thank you for your thanks over the [[Body Mass Index]] article. My wife sometimes sends thank you cards to people for sending her thank you cards but I think that is going too far! [[User:Thincat|Thincat]] 13:02, 30 March 2006 (UTC)

==Image Tagging [[:Image:Lee trundle.png]]==

{| align="CENTER" style="background-color:#FFFFFF; border:8px solid #FF0000; padding:5px;"
|-
|[[Image:Nuvola apps important.svg|30px|Warning sign]]
| <center><big>This media may be '''deleted'''.</big>
</center>
|}

Thanks for uploading '''[[:Image:Lee trundle.png]]'''. I notice the 'image' page currently doesn't specify who created the content, so the [[copyright]] status is unclear. If you have not created this media yourself then there needs to be an argument why we have the right to use the media on Wikipedia (see copyright tagging below). If you have not created the media yourself then it needs to be specified where it was found, i.e., in most cases link to the website where it was taken from, and the terms of use for content from that page.

If the media also doesn't have a copyright tag then one should be added. If you created/took the picture, audio, or video then the {{tl|GFDL-self}} tag can be used to release it under the [[GFDL]]. If you believe the media qualifies as fair use, consider reading [[Wikipedia:Fair use|fair use]], and then use a tag such as {{tlp|fairusein|article name}} or one of the other tags listed at [[Wikipedia:Image copyright tags#Fair_use]]. See [[Wikipedia:Image copyright tags]] for the full list of copyright tags that you can use.

If you have uploaded other media, consider checking that you have specified their source and copyright tagged them, too. You can find a list of 'image' pages you have edited by clicking on the "[[Special:Contributions/{{PAGENAME}}|my contributions]]" link (it is located at the very top of any Wikipedia page when you are logged in), and then selecting "Image" from the dropdown box. Note that any unsourced and untagged images will be deleted one week after they have been uploaded, as described on [[wikipedia:Criteria for speedy deletion#Images.2FMedia|criteria for speedy deletion]]. If you have any questions please ask them at the [[Wikipedia:Image legality questions|Image legality questions page]]. Thank you. [[User:CLW|CLW]] 14:06, 3 April 2006 (UTC)

==Notice==
'''Community Portal controversy:''' The Community Portal was recently reverted to a version that appeared months ago. Therefore, I've called for a vote to restore to the Community Portal the version that had developed here up until that reversion. There are three drafts competing for the privilege, each representing entirely different approaches, including the current revert version. To show your support for which design should be displayed as the Community Portal, '''''[[Wikipedia:Community Portal/Redesign#The design drafts|VOTE HERE]]'''''. Sincerely, --[[User:Go for it!|Go for it!]] 18:14, 3 April 2006 (UTC)

== Source for image ==

Howdy, whilst checking through [[:Category:Crown copyright images]], I came across [[:Image:Body mass index-weightheight.jpg]], which you uploaded under Crown copyright. Unfortunately, use of CC images requires attribution. Lacking this, I've added a fair use rationale to the page, but ideally the page could do with the source (if you remember it.) [[User:GeeJo|GeeJo]] [[User talk:GeeJo|(t)]]⁄[[Special:Contributions/GeeJo|(c)]] • 08:45, 10 May 2006 (UTC)

== You still over there, man? ==
Haven't heard from you in ages. Still with us? :) --[[User:Woohookitty|''Woohookitty'']][[User talk:Woohookitty|(meow)]] 08:05, 30 May 2006 (UTC)

Yeah, where have you been? I noticed your attempt to bring Wikipedia's Discussion pages into a bulletin-style format and I thought it was great. First I had seen that anyone ''did'' anything about it, as opposed to just talk. Any hope of reviving that effort? -[[User:Mhsia|Mhsia]] 03:41, 5 August 2006 (UTC)

'''Welcome back'''. I hope you and your family are doing well. It looks like you've been missed. I'm looking forward to working with you again. At some point, it would be a good idea to add charts, graphs, and tables to the nutrition articles, or perhaps create a separate page on statistical data. —[[User:Viriditas|Viriditas]] | [[User talk:Viriditas|Talk]] 22:13, 15 August 2006 (UTC)
:Congratulations! —[[User:Viriditas|Viriditas]] | [[User talk:Viriditas|Talk]] 22:20, 15 August 2006 (UTC)
== Possibly unfree Image:Stevekarlricky16wj.jpg ==
<div style="padding:5px; background-color:#E1F1DE;"> An image that you uploaded or altered, [[:Image:Stevekarlricky16wj.jpg]], has been listed at [[Wikipedia:Possibly unfree images]] because its copyright status is disputed. If the image's copyright status cannot be verified, it may be deleted. Please go to its [[:Image:Stevekarlricky16wj.jpg|page]] for more information if you are interested in it not being deleted. Thank you. [[User:Fritz Saalfeld|Fritz Saalfeld]] ([[User talk:Fritz Saalfeld|Talk]]) 09:42, 23 September 2006 (UTC)</div>
== Possibly unfree Image:Karlp47nj.jpg]] ==
<div style="padding:5px; background-color:#E1F1DE;"> An image that you uploaded or altered, [[:Image:Karlp47nj.jpg]]]], has been listed at [[Wikipedia:Possibly unfree images]] because its copyright status is disputed. If the image's copyright status cannot be verified, it may be deleted. Please go to its [[:Image:Karlp47nj.jpg]]|page]] for more information if you are interested in it not being deleted. Thank you. [[User:Fritz Saalfeld|Fritz Saalfeld]] ([[User talk:Fritz Saalfeld|Talk]]) 09:42, 23 September 2006 (UTC)</div>

== [[Obedience (human behavior)]] ==
Hello!

I noticed your comments about my edits to [[Obedience (human behavior)]], so I though I had better explain my edits. Please note that I did not merely revert the previous editor's contributions: instead, I copyedited them and then edited and integrated them with the previous content: see the edit history. I then expanded the article further.

I think my main objection to the previous form of the article was that almost all of it was devoted to a single topic, the [[Milgram experiment]], which is already dealt with in a much longer and better written article, and devoted very little of the article to any other discussion of obediance outside the context of the Milgram experiment.

On the other hand, you actually ''did'' revert my edits in their entirety, and in the process deleting all of the new material added. In the process, you restored every single typo and grammatical error in the original text.

As just one example, the original contains the sentence

:''The milgram was one of the first experiments used to look into the power, which authority figures exude, as well as the extent of the orders participants would go to due to these influences.''

This is, by any standards, a terrible piece of writing. What is "the milgram"? Is it Stanley Milgram, or his experiment? Why the misplaced commas? Do authority figures ''literally'' exude power? What does "the extent of the orders participants would go to due to these influences" mean? Does it mean that the participants went to the orders -- possibly to pick them up in person? How great was their extent? And so forth.

Now, I replaced this by the sentence

:''The Milgram experiment was one of the first experiments used to look into the power of authority figures as well as the length which participants would go to due to these influences.''

I believe that this has the meaning intended by the writer of the previous sentence, and is at least in reasonably grammatical English, although it could be made considerably better -- for example, "study" would have been better than "look into".

By the way, I should apologize for the intemperate tone of some of my edit comments -- rest assured, they represent only exasperation with the copyediting required, rather than being a symptom of religious mania, and are entirely non-denominational.

Please ''edit'' articles, rather than blindly reverting them. Where other editors excise material, why not add a cite when you restore it?

I will try to integrate the two sets of edits into a coherent whole, taking your comments into account, and see if I can produce a version that is acceptable to all. -- [[User:The Anome|The Anome]] 23:28, 27 September 2006 (UTC)

Please now see [http://en.wikipedia.org/w/index.php?title=Obedience_%28human_behavior%29&oldid=78211787 the current version of the article as of this comment], which is the result of over 20 step-by-step edits with attached edit comments in which I explain what I am doing at each step. I have carefully attempted to preserve the material you are concerned about, with one exception: I have replaced the very first sentence of the article with the first two sentences of the earlier version, since I think that's a better definition of "obedience". Yes, almost every part of the article has changed in some way, but the changes are carefully described in the edit comments, and consist mainly of merges and restructuring of the previous material with the addition of only the new material added later, and minor copyedits for grammar and spelling. -- [[User:The Anome|The Anome]] 00:36, 28 September 2006 (UTC)

I've done some final polishing, and have also included the Persaud quote and the cite you helpfully gave me. Now, if you have any objections to my edits, would you please characterize them on the talk page of the article and attempt to correct them ''by editing the article'', rather than, for example, not really bothering to read through the changes at all to the point that you mistake them for a simple revert and describe the new version as "dog shite". -- [[User:The Anome|The Anome]] 00:55, 28 September 2006 (UTC)

== [[:Wikipedia:WikiProject Nutrition]] ==

This is to inform you that the project page you created above has been marked as a candidate for deletion in accord with wikipedia policy. Please feel free to follow the links at the project page to participate in the discussion. Thank you. [[User:Badbilltucker|Badbilltucker]] 15:14, 5 October 2006 (UTC)

== [[n:Image:TopLogoGoalkeeper freetouse pleasebelieveme i am not lying.png]] ==

Please be advised that is has been requested for deletion by [[n:User:Stevenfruitsmaak]] on [[n:WN:DR]]. [[User:Bawolff|Bawolff]] 01:01, 20 October 2006 (UTC)
==License tagging for Image:Ricky gervais from flickr.png==
Thanks for uploading [[:Image:Ricky gervais from flickr.png]]. Wikipedia gets thousands of images uploaded every day, and in order to verify that the images can be legally used on Wikipedia, the source and copyright status must be indicated. Images need to have an [[Wikipedia:Image copyright tags|image tag]] applied to the [[Wikipedia:Image description page|image description page]] indicating the copyright status of the image. This uniform and easy-to-understand method of indicating the license status allows potential re-users of the images to know what they are allowed to do with the images.

For more information on using images, see the following pages:
* [[Wikipedia:Image use policy]]
* [[Wikipedia:Image copyright tags]]

This is an automated notice by [[User:OrphanBot|OrphanBot]]. If you need help on selecting a tag to use, or in adding the tag to the image description, feel free to post a message at [[Wikipedia:Media copyright questions]]. 00:11, 30 November 2006 (UTC)

== Thanks... ==

...for the prettyfying edits to WikiProject Chemistry :-) How did you come across it? I haven't seen you around before. --[[User:HappyCamper|HappyCamper]] 18:52, 6 December 2006 (UTC)

:Of course! We actually had something like that in our WikiProject, but I think it died down a while ago. Might be good and resurrect that, but I'm willing to jump on board anywhere and make a few sustained edits to articles. --[[User:HappyCamper|HappyCamper]] 18:57, 6 December 2006 (UTC)

::You know, that just warms my Wikipedian soul...I'm sure the others will be happy too! --[[User:HappyCamper|HappyCamper]] 19:47, 6 December 2006 (UTC)

:::Okay, now, um...can you explain how to use the collaboration thingy? --[[User:HappyCamper|HappyCamper]] 01:27, 8 December 2006 (UTC)

{| style="border: 1px solid {{{border|gray}}}; background-color: {{{color|#fdffe7}}};"
|rowspan="2" valign="top" | [[Image:Barnstar-atom3.png|100px]]
|rowspan="2" |
|style="font-size: x-large; padding: 0; vertical-align: bottom; height: 1.1em;" | '''The E=mc² Barnstar'''
|-
|style="vertical-align: top; border-top: 1px solid gray;" | I award thee this barnstar for good work. :-) [[Image:SConfident.gif|15px]] [[User:JCraw|J O R D A N]] <nowiki>[</nowiki>[[User talk:JCraw|talk]] <nowiki>]</nowiki> 14:52, 8 December 2006 (UTC)
|}

== Image:Ordinary Boys.jpg ==
Thanks for uploading '''[[:Image:Ordinary Boys.jpg]]'''. I notice the 'image' page specifies that the image is being used under [[Wikipedia:Fair use|fair use]], but its use in Wikipedia articles fails our [[Wikipedia:Fair use criteria|first fair use criterion]] in that it illustrates a subject for which a freely licensed image could reasonably be found or created that provides substantially the same information. If you believe this image is not replaceable, please:

# Go to [[:Image:Ordinary Boys.jpg|the image description page]] and edit it to add <code><nowiki>{{Replaceable fair use disputed}}</nowiki></code>, '''without deleting the original Replaceable fair use template'''.
# On [[Image talk:Ordinary Boys.jpg|the image discussion page]], write the reason why this image is not replaceable at all.

Alternatively, you can also choose to replace the fair use image by finding a freely licensed image of its subject, [[Wikipedia:Requesting copyright permission|requesting that the copyright holder release this (or a similar) image under a free license]], or by taking a picture of it yourself.

If you have uploaded other fair use media, consider checking that you have specified how these images fully satisfy our fair use criteria. You can find a list of 'image' pages you have edited by clicking on [{{fullurl:Special:Contributions|target={{PAGENAMEE}}&namespace=6}} this link]. Note that any fair use images which are replaceable by free-licensed alternatives will be deleted one week after they have been uploaded, as described on [[Wikipedia:Criteria for speedy deletion#Images.2FMedia|criteria for speedy deletion]]. If you have any questions please ask them at the [[Wikipedia:Media copyright questions|Media copyright questions page]]. Thank you. [[User:ShadowHalo|ShadowHalo]] 19:19, 12 December 2006 (UTC)

==[[Physical Chemistry]]==

A good start in cleaning this up. Have you seen [[Wikipedia:WikiProject Physical Chemistry]] and the related talk page? It is a fairly new WikiProject and the participants seem very busy. We need you help. --[[User:Bduke|Bduke]] 21:34, 28 December 2006 (UTC)
:Thanks for your comment on my talk page. Keep the discussion here. Moving from one page to the other loses the thread. "Chemical Physics" is an acceptable term. It could be defined as the chemistry that physicists do, or alternatively what might appear in the "Journal of Chemical Physics", which is published by the Americal Institute of Physics, as opposed to the "Journal of Physical Chemistry" which is published by the American Chemical Society. One the other hand I have had papers rejected by both but then accepted by the other and I would not have said one was more physics and the other more chemistry. On other matters on [[Physical Chemistry]], I'll try to help but I'm tied up with family. The two notes are unclear - what book are they refering to? You need to update the text references to the latest edition. I have the latest Atkins so I'll fix that. --[[User:Bduke|Bduke]] 22:22, 28 December 2006 (UTC)
::Well, i've read lots and lots of chemistry, but my major is physics, so i'm going to have to do some reading up on the history and other concepts. It's been some time since i've done some chemistry practically.. there's a lot of things i've done in organic chemistry and inorganic chemistry, but there's not much i've done in physical chemistry research so i'll be pretty much needing to get a brand new book on it, because the ones i have are the ones i bought whilst i was in university! Well, i'd be glad to contribute towards the physical chemistry wikiproject, just give me a few days to aquaint myself to the other "mid-concepts" of physical chemistry and link them to what i already know about thermodynamics. In terms of quantum mechanics and particulate theory.. i did years of it :-/.

Cheers :-) [[User:JSpudeman|James S]] 22:28, 28 December 2006 (UTC)

== CManifesto vandalism ==
Thanks for dealing with CManifesto (who apparently spammed the technical village pump, among other places). I was just putting the vandalism warning on his Talk Page, when that became an edit conflict. So, I'm guessing you redirected his Talk page to his User page, to prevent the meta-spam of people editting his talk page with vandalism warnings & such? [[User:PeterStJohn|Peter H. St.John, M.S.]] 19:56, 17 January 2007 (UTC)

== Possibly unfree Image:Brandon vedas.jpg ==
<div style="padding:5px; background-color:#E1F1DE;"> An image that you uploaded or altered, [[:Image:Brandon vedas.jpg]], has been listed at [[Wikipedia:Possibly unfree images]] because its copyright status is disputed. If the image's copyright status cannot be verified, it may be deleted. Please go to its [[:Image:Brandon vedas.jpg|page]] for more information if you are interested in it not being deleted. Thank you. [[User:Mosmof|Mosmof]] 16:08, 20 January 2007 (UTC)</div>

== Image:Brentoggmonstercamera.jpg ==
Thanks for uploading '''[[:Image:Brentoggmonstercamera.jpg]]'''. I notice the 'image' page specifies that the image is being used under [[Wikipedia:Fair use|fair use]], but its use in Wikipedia articles fails our [[Wikipedia:Fair use criteria|first fair use criterion]] in that it illustrates a subject for which a freely licensed image could reasonably be found or created that provides substantially the same information. If you believe this image is not replaceable, please:

# Go to [[:Image:Brentoggmonstercamera.jpg|the image description page]] and edit it to add <code><nowiki>{{Replaceable fair use disputed}}</nowiki></code>, '''without deleting the original Replaceable fair use template'''.
# On [[Image talk:Brentoggmonstercamera.jpg|the image discussion page]], write the reason why this image is not replaceable at all.

Alternatively, you can also choose to replace the fair use image by finding a freely licensed image of its subject, [[Wikipedia:Requesting copyright permission|requesting that the copyright holder release this (or a similar) image under a free license]], or by taking a picture of it yourself.

If you have uploaded other fair use media, consider checking that you have specified how these images fully satisfy our fair use criteria. You can find a list of 'image' pages you have edited by clicking on [{{fullurl:Special:Contributions|target={{PAGENAMEE}}&namespace=6}} this link]. Note that any fair use images which are replaceable by free-licensed alternatives will be deleted one week after they have been uploaded, as described on [[Wikipedia:Criteria for speedy deletion#Images.2FMedia|criteria for speedy deletion]]. If you have any questions please ask them at the [[Wikipedia:Media copyright questions|Media copyright questions page]]. Thank you. [[User:Mosmof|Mosmof]] 16:08, 20 January 2007 (UTC)
: For this image, the DVD fair use doesn't apply, since it's being used to describe the photograph's subject, who is a living person who makes public appearances, and it's reasonably possible to get a free picture of him.

:Which is why [[:Image:Stephenmerchant large.jpg]] has been tagged as replaceable as well. You had originally tagged the photo as public domain, which definitely wasn't the case because the [http://www.flickr.com/photos/jonappleyard/158012294/in/set-72157594152108959/ the source] clearly says "All rights reserved". Unless the license is changed, it has to fall under fair use, as it's a copyrighted image. [[User:Mosmof|Mosmof]] 16:08, 20 January 2007 (UTC)

==Snell's law writing==

Jay, I have the impression that you either still don't understand Snell's law, or you don't know how to construct intelligible English sentences and paragraphs. It seems you keep trying to work on the lead, but can't see how what you are doing changes the meaning, scrambles the structure, and introduces errors. Please be more cautious, or check your proposed changes with me or others on the talk page. [[User:Dicklyon|Dicklyon]] 18:50, 21 January 2007 (UTC)

User talk:JSpudeman

2007-01-21T19:11:02Z

JSpudeman:

[[Image:Wikimedia-logo.svg|45px|left]] <div style="font-size:24px; letter-spacing: 1.1px;" align="left"> Spude-pedia commons
</div> 
<div style="width: 96%; border: 2px #000 solid; padding: 20px 20px 20px 20px; margin: 0px 0px 0px 0px; font-family: Bitstream Vera Sans, sans-serif, verdana; letter-spacing: 1.2px; background-color: rgb(247,210,130); margin:0em 0em 0em 0em; border:2px solid #000; -moz-border-radius:20px;">
=== Archived Talks ===
{| border=1 cellpadding=6 cellspacing=0
|style="background-color:#DDDDDD;" |[[User talk:Spum/archive01|Archive 1]]
|The "Wild" months.
|----
|style="background-color:#DDDDDD;" |[[User talk:Spum/archive02|Archive 2]]
|Normality.
|----
|style="background-color:#DDDDDD;" |[[User talk:JSpudeman/archive03|Archive 3]]
|The end of the road.
|}

User:JSpudeman

2007-01-21T19:09:31Z

JSpudeman: Well, neverdmind.

See ya.

Body mass index

2007-01-21T18:40:13Z

JSpudeman: Removed HUGE BMI table; add it to wikisource if you want.

[[Image:Body_mass_index_chart.svg|right|290px|thumb|An example of a body mass index chart]]'''Body mass index''' ('''BMI''') or '''Quetelet Index''' is a statistical measure of the weight of a person scaled according to height. It was invented between 1830 and 1850 by the [[Belgium|Belgian]] [[polymath]] [[Adolphe Quetelet]] during the course of developing "social physics".

==Calculation==
BMI is defined as the individual's [[body weight|body mass]] divided by the square of the height, and is almost always expressed in the unit <math>\mathrm{kg}/\mathrm{m}^2</math>, which is therefore often left out. The BMI value can be calculated with the following formulae.
<center>
{| class="wikitable" | style="font-weight:bold; text-align:center;"
|[[International System of Units|SI]] units
| [[Imperial unit|Imperial]] units
|-
| <math>\mathrm{BMI} = \frac{\mathit{mass} \ \mathrm{(kg)}}{\mathit{height}^2 (\mathrm{m})}</math>
| <math>\mathrm{BMI} = 703 \frac{\mathit{weight} \ (\mathrm{lb})}{\mathit{height}^2 \ (\mathrm{in})}</math>
|}
</center>

When calculating BMI, using [[International System of Units|SI]] units is preferred.

==Usage==
The BMI has become controversial because many people, including physicians, have come to rely on it for medical diagnosis - but that has never been the BMI's purpose. It is meant to be used as a simple means of classifying sedentary (physically inactive) individuals with an average body composition.{{cn}} For these individuals, the current value settings are as follows: a BMI of 18.5 to 25 may indicate optimal weight; a BMI lower than 18.5 suggests the person is [[underweight]] while a number above 25 may indicate the person is [[overweight]]; a BMI below 15 may indicate the person has an [[eating disorder]]; a number above 30 suggests the person is [[obesity|obese]] (over 40, morbidly obese).

In [[physiology]] the term “[[weight]]” is used interchangeably with “[[mass]]”. For a given body shape and given density, the BMI will be proportional to height e.g. if all body dimensions increase by 50%, the BMI increases by 50%.

Generally, a BMI chart displays calculated BMI as a function of weight (horizontal axis) and height (vertical axis) using “contour lines” for different values of BMI or colors for different BMI categories.

==Accuracy==
The BMI is meant to broadly categorise populations for purely statistical purposes. As noted, its accuracy in relation to actual levels of body fat is easily distorted by such factors as fitness level, muscle mass, bone structure, gender, and ethnicity. People who are [[mesomorphic]] tend to have higher BMI numbers than people who are [[endomorphic]], because they have greater bone mass and greater muscle mass, respectively, than do endomorphic individuals.

Similarly, an [[ectomorphic]] individual could conceivably receive an unhealthily low reading, when in fact their body type makes them naturally thin no matter what they eat.

People with [[short stature]] tend to have lower BMI. Therefore they should use a lower cut-off value for obesity diagnosis.<ref>[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12700010&dopt=Abstract Short stature is related to high body fat composition despite body mass index in a Mexican population], Lopez-Alvarenga JC, Montesinos-Cabrera RA, Velazquez-Alva C, Gonzalez-Barranco J., Arch Med Res. 2003 Mar-Apr;34(2):137-40</ref> The same applies to older people, whose reduced muscle mass can hide additional body fat without increasing BMI.

== BMI categories ==

A frequent use of the BMI is to assess how much an individual's body weight departs from what is normal or desirable for a person of his or her height. The weight excess or deficiency may, in part, be accounted for by body fat ([[adipose tissue]]) although other factors such as muscularity also affect BMI (see discussion below and [[overweight]]). Human bodies rank along the index from around 15 (near starvation) to over 40 (morbidly obese). This statistical spread is usually [[Descriptive statistics|described]] in broad categories: underweight, normal weight, overweight, obese and morbidly obese. The particular BMI values used to demarcate these categories varies based on the authority, but typically a BMI of less than 18.5 is considered underweight and may indicate [[malnutrition]], an [[eating disorder]], or other health problems, while a BMI greater than 25 is considered overweight and above 30 is considered [[obesity|obese]]. These ranges of BMI values are valid only when applied to adults.

=== Thresholds ===
Given the reservations detailed below concerning the limitations of the BMI as a diagnostic tool for individuals, the following are common definitions of BMI categories:

:* Starvation: less than 15
:* Anoretic(n.)/Anorexic(adj.): less than 17.5
:* Underweight: less than 18.5
:* Ideal: from 18.5 to 25
:* Overweight: from 25 to 30
:* Obese: from 30 to 40
:* Morbidly Obese: greater than 40

The U.S. National Health and Nutrition Examination Survey of [[1994]] indicates that 59% of American men and 49% of women have BMIs over 25. Extreme obesity — a BMI of 40 or more — was found in 2% of the men and 4% of the women. There are differing opinions on the threshold for being underweight in females, doctors quote anything from 18.5 to 20 as being the lowest weight, the most frequently stated being 19. A BMI nearing 15 is usually used as an indicator for starvation and the health risks involved, with a BMI <17.5 being one of the [[Diagnostic and Statistical Manual of Mental Disorders|DSM]] criteria for the diagnosis of [[anorexia nervosa]].

===BMI-for-age===
BMI is used differently for children. It is calculated the same way as for adults, but then compared to typical values for other children of the same age. Instead of set thresholds for underweight and overweight, then, the BMI [[percentile]] allows comparison with children of the same gender and age.<ref>[http://www.cdc.gov/nccdphp/dnpa/bmi/bmi-for-age.htm BMI - Body Mass Index: BMI for Children and Teens]</ref> A BMI that is less than the 5th percentile is considered underweight and above the 95th percentile is considered overweight. Children with a BMI between the 85th and 95th percentile are considered to be at risk of becoming overweight.

Recent studies in England have indicated that females between the ages 12 and 16 have a higher BMI than males by 1.0 kg/m² on average.<ref>[http://www.archive2.official-documents.co.uk/document/deps/doh/survey02/summ03.htm Health Survey for England: The Health of Children and Young People]</ref>

===International variations===
These recommended distinctions along the linear scale may vary from time to time and country to country, making global, longitudinal surveys problematic. In 1998, the U.S. [[National Institutes of Health]] brought U.S. definitions into line with [[World Health Organization]] guidelines, lowering the normal/overweight cut-off from BMI 27.8 to BMI 25. This had the effect of redefining approximately 30 million Americans, previously "technically healthy" to "technically overweight". It also recommends lowering the normal/overweight threshold for South East Asian body types to around BMI 23, and expects further revisions to emerge from clinical studies of different body types.

In Singapore, the BMI cut-off figures were revised in 2005 with an emphasis on health risks instead of weight. Adults whose BMI is between 18.5 and 22.9 have a low risk of developing heart disease and other health problems such as diabetes. Those with a BMI between 23 and 27.4 are at moderate risk while those with a BMI of 27.5 and above are at high risk of heart disease and other health problems.[http://www.hpb.gov.sg/hpb/default.asp?TEMPORARY_DOCUMENT=1769&TEMPORARY_TEMPLATE=2 Singapore BMI Cut-offs.]

== Applications ==
=== Statistical device ===
The Body Mass Index is generally used as a means of correlation between groups related by general mass and can serve as a basic means of estimating [[adipose tissue|adiposity]]. However, the duality of the Body Mass Index is that, whilst easy-to-use as a general calculation, it is limited in how accurate and pertinent the data obtained from it can be. Generally, the Index is suitable for recognising trends within sedentary or overweight individuals because there is a smaller margin for errors.<ref>Jeukendrup, A & Gleeson, M. (2005) ''Sports Nutrition'' Human Kinetics</ref>

This general correlation is particularly useful for consensus data regarding obesity or various other conditions because it can be used to build a semi-accurate representation from which a solution can be stipulated, or the [[Recommended Dietary Allowance|RDA]] for a group can be calculated. Similarly, this is becoming more and more pertinent to the growth of children, due to the majority of their exercise habits.<ref>Barasi, M. E (2004) ''Human Nutrition - a health perspective''</ref>

The growth of children is usually documented against a BMI-measured growth chart. Obesity trends can be calculated from the difference between the child's BMI and the BMI on the chart. However, this method again falls prey to the obstacle of body composition: many children who are generally born, or grow as an [[Endomorphic|endomorph]], would be classed as obese despite body composition. Clinical professionals should take into account the child's body composition and defer to an appropriate technique such as [[densiometry]].

=== Clinical practice ===
BMI can be calculated quickly and without expensive equipment. However, BMI categories do not take into account factors such as [[frame size]] and muscularity.<ref>Jeukendrup, A & Gleeson, M. (2005) ''Sports Nutrition'' Human Kinetics</ref> The categories also fail to account for varying proportions of muscle, fat, bone & cartilage, and water weight.

Despite this, BMI categories are generally regarded as a satisfactory tool for measuring whether sedentary individuals are "underweight," "overweight" or "obese." It has been used by the [[World Health Organization|'''WHO''']] as the standard for recording obesity statistics since the early [[1980]]s. In the United States, BMI is also used as a measure of underweight, owing to advocacy on behalf of those suffering with eating disorders, such as [[anorexia nervosa]] and [[bulimia nervosa]].

Individuals who are not sedentary - especially athletes - as well as children, the elderly, the infirm, and individuals who are naturally [[endomorphic]] or [[ectomorphic]] (i.e., people who don't have a medium frame) are ill-fitted to assessment using the BMI. Or to state the problem more accurately, the BMI measurements at which these people may be underweight, overweight or obese are different from sedentary [[mesomorphic|mesomorphs]] whose ages are between about 20 and 70.

In athletes, the problem is that muscle is denser than fat. Most professional athletes are "overweight" or "obese" according to their BMI - unless the number at which they are considered "overweight" or "obese" is adjusted upward. In children and the elderly, differences in bone density and, thus, in the proportion of bone to total weight can mean the number at which these people are considered ''under''weight should be adjusted downward.

In all cases, methods for actually measuring [[body fat percentage]] are always preferable to BMI for measuring healthy body size.

=== Problems ===

The '''units''' associated with Body Mass Index are problematic. Body Mass Index is expressed in "kilograms per meter squared" or "pounds per inch squared", depending on which Quetelet equation is used. "Pounds per inch squared" translates into "force per unit area", which, in turn, is a unit of '''pressure''' in physics. This is confusing, since BMI is an index reflecting total body fat content, rather than an index of body pressure. A simple modification of the BMI system, called "'''BMI Prime'''", was proposed to eliminate the use of these confusing units. By definition, '''BMI Prime is the ratio of a person's Actual Weight (or Mass) to his/her Upper Weight (or Mass) Limit, calculated at a BMI of 24.9'''. Since BMI Prime is a ratio, it is expressed as a pure, dimensionless number. Another advantage of the "'''BMI Prime'''" system is that it enables people, at a glance, to determine what percentage they deviate from their Upper Weight (Mass) Limit. For further details: [http://www.surgicalassociatesofwestport.com/html/Surgical%20Assoc%20BMI%20Website.htm Quetelet's Equation, Upper Weight Limits, and BMI Prime]

As a general rule, developed muscle is denser than fat and the BMI does not account for this. Therefore a person with more muscle mass, such as a body-builder, will seem to be overweight. Likewise it could be stipulated that some long-distance or endurance athletes would be classified as [[ectomorphic]] (underweight, anorexic or starvation), this type of athlete tends to have low body fat and well developed slow twitch muscle, which does not contribute greatly to muscle mass. These individuals could be widely regarded as the perfect composite for their particular sports. Due to these limitations, body composition for athletes would not be calculated using the body mass index, and instead the [[Body fat percentage|body fat]] would be determined by such techniques as skinfold measurements or underwater weighing. In parallel to this, sportsmen or women from sports such as [[Rugby football|Rugby]] and [[American Football]], where size and muscle are often of importance, could be listed as overweight, due to a large amount of muscle. At the extreme, many [[bodybuilding|bodybuilders]] would be classified as morbidly obese, such as [[Markus Rühl]] who has a BMI of 46.

Another issue is that competitive athletes often know very accurately what their actual height and weight are, while the general public has tendencies toward over-estimating their height, and under-estimating their weight. The BMI standards, as a public health tool, take this tendency into account. This can lead to athletes having a higher reported BMI than a lay person of the same height and weight.{{cn}}

Mayo Clinic researchers say the BMI doesn't accurately predict risk of cardiovascular death because it doesn't distinguish between muscle and fat. They say a better measure may be your [[Waist-hip ratio]].

In an analysis led by Lopez-Jiminez of 40 studies involving 250,000 people, heart patients with normal BMIs were at higher risk of death from cardiovascular disease than people whose BMIs put them in the "obese" range.

In fact, the ones in the study who had the highest death rates were people who weighed the least; in other words, they had the lowest BMIs.

== References ==
<references />


==See also==
{{wikisource}}
* [[Body fat percentage]]
* [[Muscle]]
* [[Muscle mass]]
* [[Skeletal muscle]]
* [[Basal metabolic rate]]

==External links==

* Online BMI Calculator (in [http://nhlbisupport.com/bmi/bmicalc.htm Imperial] or [http://nhlbisupport.com/bmi/bmi-m.htm metric] system) (National Heart, Lung, and Blood Institute)
* U.S. National Centre for Health Statistics [http://www.cdc.gov/growthcharts/ BMI Growth Charts for children and young adults]
* BMI Calculator [http://www.josxp.com/component/option,com_bmi/ Cute BMI Calculator]
* BMI Calculator for Mobile Phones [http://gsmdev.com/projects/gdbmi/ gdBMI]
*[http://www.surgicalassociatesofwestport.com/html/Surgical%20Assoc%20BMI%20Website.htm Quetelet's Equation, Upper Weight Limits, and BMI Prime]
*[http://www.projectweightloss.com/ BMI calculator and calorie counter.] Calculates BMI as well as recommended ranges, based on age, weight and height.
[[Category:Human appearance]]
[[Category:Medical signs]]
[[Category:Mass]]
[[Category:Nutrition]]
[[Category:Obesity]]

[[ca:Índex de massa corporal]]
[[cs:Index tělesné hmotnosti]]
[[da:BMI]]
[[de:Body-Mass-Index]]
[[es:Índice de masa corporal]]
[[eo:Korpomasa indico]]
[[fa:نمایه جرم بدن]]
[[fr:Indice de masse corporelle]]
[[hr:Indeks tjelesne mase]]
[[it:Indice di massa corporea]]
[[he:BMI]]
[[ms:Index Jisim Badan]]
[[nl:Queteletindex]]
[[ja:ボディマス指数]]
[[pl:BMI]]
[[pt:Índice de massa corporal]]
[[ru:Индекс массы тела]]
[[simple:Body mass index]]
[[sk:Index telesnej hmotnosti]]
[[fi:Painoindeksi]]
[[sv:BMI]]
[[th:ดัชนีมวลกาย]]
[[vi:Chỉ số khối cơ thể]]
[[zh:身高體重指數]]

Snell's law

2007-01-21T18:25:24Z

JSpudeman: Fixed up the one-line-floater

[[Image:Snells law.svg|thumb|300px|[[Refraction]] of light at the interface between two media of different [[refractive index|refractive indices]], with n2 > n1. Since the velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.]]

In [[optics]] and [[physics]], '''Snell's law''' (also known as '''Descartes' Law''' or the '''law of refraction'''), is a [[mathematical formula|formula]] used in [[ray tracing]] and [[theory]] to describe the relationship between the angles of incidence and refraction, when referring to light or other [[wave]]s, passing through a boundary between two different [[isotropic]] [[medium (optics)|media]], such as air and glass.

Named for one of it's discoverers, [[Willebrord Snellius]], the law states that the ratio of the [[sine]]s of the angles of incidence and refraction are a constant value, depending upon the media, which is also obtained through the ratio of [[velocities]] in the two media, or equivalently, the inverse ratio of the indices of refraction:

{| cellspacing="10"
|<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{n_2}{n_1}</math>
| or
|<math>n_1\sin\theta_1 = n_2\sin\theta_2\ </math>
|}

Snell's law follows from [[Fermat]]'s [[Fermat's principle|principle of least time]], which in turn follows from the propagation of light as waves.
== History ==
[[Image:Snell Law of Sines 1837.png|thumb|right|300px|An 1837 view of the history of "the Law of the Sines"<ref>William Whewell, ''History of the Inductive Science from the Earliest to the Present Times'', London: John H. Parker, 1837.</ref>]]
Snell's law was first discovered and described by [[Ibn Sahl]] in a manuscript written c.[[984]],<ref>{{cite journal | author=Rashed, Roshdi | title= A pioneer in anaclastics: Ibn Sahl on burning mirrors and lenses | journal= [[Isis (journal)|Isis]]| year= 1990| volume= 81| pages= 464–491 |doi=10.1086/355456}}</ref> who used it to work out the shapes of lenses that focus light with no geometric aberrations, known as [[anaclastic lens]]es. It was discovered again by [[Thomas Harriot]] in [[1602]],<ref>{{cite journal | author=Kwan, A., Dudley, J., and Lantz, E. | title=Who really discovered Snell's law? | journal=[[Physics World]] | year=2002 | volume=15 | issue=4 | pages=64 |url=http://physicsworldarchive.iop.org/index.cfm?action=summary&doc=15%2F4%2Fphwv15i4a44%40pwa-xml&qt=}}</ref> who did not publish his work.

In [[1621]], it was discovered yet again by Willebrord Snel, in a mathematically equivalent form, but unpublished during his lifetime. [[René Descartes]] independently derived the law using heuristic momentum conservation arguments in terms of sines in his [[1637]] treatise ''[[Discourse on Method]]'' (though detractors such as Fermat accused Descartes of working toward the already known answer with sophistic reasoning), and used it to solve a range of optical problems. Rejecting Descartes' solution, Pierre de Fermat arrived at the same solution based solely on his principle of least time.

In [[French language|French]], Snell's Law is called "la loi de Descartes" or "loi de Snell-Descartes."

[[Image:Huygens Refracted Waves.png|left|thumb|125px|Huygens's construction]]

In his 1678 ''Traité de la Lumiere'', [[Christiaan Huygens]] showed how Snell's law of sines could be explained by, or derived from, the wave nature of light, using what we have come to call the [[Huygens–Fresnel principle]].

== Explanation ==
Snell's law is used to determine the direction of light rays though refractive media with varying indices of refraction. The indices of refraction of the media, labeled <math>n_1,n_2</math> and so on, are used to represent the factor by which light is "slowed down" within a refractive medium, such as glass or water, compared to its velocity in a vacuum.

As light passes the border between media, depending upon the relative refractive indices of the two media, the light will either be refracted to a lesser angle, or a greater one. These angles are measured with respect to the ''normal line'', represented perpendicular to the boundary. In the case of light traveling from air into water, light would be refracted towards the normal line, due to the fact that the light is slowed down in water; light traveling from water to air would refract away from the normal line.

Refraction between two surfaces is also referred to as ''reversible'' due to the fact that if all conditions were identical, the angles would be the same for light propagating in the opposite direction.

Snell's law is only generally true for isotropic or specular media (such as [[glass]]). In [[anisotropic]] media such as some [[crystal]]s, [[birefringence]] may split the refracted ray into two rays, the ''ordinary'' or ''o''-ray which follows Snell's law, and the other ''extraordinary'' or ''e''-ray which may not be co-planar with the incident ray.

When the light or other wave involved is monochromatic, that is, of a single frequency, Snell's law can also be expressed in terms of a ratio of wavelengths in the two media, λ1 and λ2:

:<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{\lambda_1}{\lambda_2}</math>

=== Total internal reflection and critical angle ===
[[Image:Refraction internal reflection diagram.PNG|thumb|220px|right|An example of the angles involved within total internal reflection.]]
When light moves from a dense to a less dense medium, such as from water to air, Snell's law cannot be used to calculate the refracted angle when the resolved sine value is higher than 1. At this point, light is reflected in the incident medium, known as internal reflection. Before the ray totally internally reflects, the light refracts at the '''critical angle'''; it travels directly along the surface between the two refractive media, without a change in phases like in other forms of optical phenomena.

As an example, a ray of light is incident at <math>50^o</math> towards a water–air boundary. If the angle is calculated using Snell's Law, then the resulting sine value will not invert, and thus the refracted angle cannot be calculated by Snell's law, due to the absense of a refracted outgoing ray:

:<math>\theta_2 = \sin^{-1} (\frac{n_1}{n_2}\sin\theta_1) = \sin^{-1} (\frac{1.333}{1.000}0.766) = \sin^{-1} 1.021</math>

In order to calculate the critical angle, let <math>\theta_2 = 90^o</math> and solve for <math>\theta_\mathrm{crit}</math>:

:<math>\theta_{\mathrm{crit}} = \sin^{-1} \left( \frac{n_2}{n_1} \right)</math>

When θ1 > θcrit, no refracted ray appears, and the incident ray undergoes [[total internal reflection]] from the interface medium.

=== Derivations ===
Snell's law may be derived from [[Fermat's principle]], which states that the light travels the path which takes the least time. By taking the [[derivative]] of the [[optical path length]], the [[stationary point]] is found giving the path taken by the light (though it should be noted that the result does not show light taking the least time path, but rather one that is stationary with respect to small variations as there are cases where light actually takes the greatest time path, as in a spherical mirror).

Alternatively, Snell's law can be derived using interference of all possible paths of light wave from source to observer—it results in destructive interference everywhere except extrema of phase (where interference is constructive)—which become actual paths. In a classic analogy by [[Richard Feynman]], the area of lower refractive index is replaced by a beach, the area of higher refractive index by the sea, and the fastest way for a rescuer on the beach to get to a [[drowning]] person in the sea is to run along a path that follows Snell's law.

Another way to derive Snell’s Law involves an application of the general [[boundary conditions]] of [[Maxwell equations]] for [[electromagnetic radiation]].

== Uses ==
=== Calculating refractive indices ===

In the diagram on the right, two media of refractive indices ''n''1 (on the left) and ''n''2 (on the right) meet at a surface or interface (vertical line). ''n''2 > ''n''1, and light has a slower [[phase velocity]] within the second medium.

A light ray '''PO''' in the leftmost medium strikes the interface at the point '''O'''. From point '''O''', we project a straight line at right angles to the line of the interface; this is known as the [[Surface normal|normal]] to the surface (horizontal line). The angle between the normal and the light ray '''PO''' is known as the ''angle of incidence'', θ1.

The ray continues through the interface into the medium on the right; this is shown as the ray '''OQ'''. The angle it makes to the normal is known as the ''angle of refraction'', θ2.

:<math>n_1 \sin\theta_1 = n_2 \sin\theta_2 </math> or <math>\sum_{k=x,y}^N x=n_x\sin\theta_x,n_y \sin\theta_y</math>
:<math>\frac{n_1}{n_2} = \frac{\sin\theta_2}{\sin\theta_1}</math>
Note that, for the case of θ1 = 0° (i.e., a ray perpendicular to the interface) the solution is θ2 = 0° regardless of the values of ''n''1 and ''n''2-- a ray entering a medium perpendicular to the surface is never bent.

The above is also valid for light going from a dense to a less dense medium; the symmetry of Snell's law shows that the same ray paths are applicable in opposite direction.

A qualitative rule for determining the direction of refraction is that the ray in the denser medium is always closer to the normal. An analogy often used to remember this is done by visualizing the ray as a car crossing the boundary between asphalt (the less dense medium) and mud (the denser medium). Depending on the angle, either the left wheel or the right wheel of the car will cross into the new medium first, causing the car to swerve.

=== Vector form ===

Given a normalized ray vector '''v''' and a normalized plane normal vector '''p''', one can work out the normalized reflected and refracted rays:

:<math>\cos\theta_1=\mathbf{v}\cdot\mathbf{p}</math>
:<math>\cos\theta_2=\sqrt{1-\left(\frac{n_1}{n_2}\right)^2\left(1-\left(\cos\theta_1\right)^2\right)}</math>
:<math>\mathbf{v}_{\mathrm{reflect}}=\mathbf{v}-\left(2\cos\theta_1\right)\mathbf{p}</math>
:<math>\mathbf{v}_{\mathrm{refract}}=\left(\frac{n_1}{n_2}\right)\mathbf{v} + \left(\cos\theta_2 - \frac{n_1}{n_2}\cos\theta_1\right)\mathbf{p}</math>
Note: <math>\mathbf{v}\cdot\mathbf{p}</math> must be positive.

The cosines may be recycled and used in the [[Fresnel equations]] for working out the intensity of the resulting rays. During total internal reflection an [[evanescent wave]] is produced, which [[exponential decay|rapidly decays]] from the surface into the second medium. Conservation of energy is maintained by the circulation of energy across the boundary, averaging to zero net energy transmission.

==Dispersion==

In many wave-propagation media, wave velocity changes with frequency or wavelength of the waves; this is true of light propagation in most transparent substances other than a vacuum. These media are called dispersive. The result is that the angles determined by Snell's law also depend on frequency or wavelength, so that a ray of mixed wavelengths, such as white light, will spread or disperse. Such dispersion of light in glass or water underlies the origin of [[rainbow]]s, since different wavelenghts appear as different colors.

In optical instruments, [[dispersion (optics)|dispersion]] leads to [[chromatic aberration]], a color-dependent blurring that sometimes is the resolution-limiting effect. This was especially true in [[refracting telescope]]s, before the invention of achromatic objective lenses.

==See also==

* [[Fresnel equations]]
* [[Reflection (physics)|Reflection]]
* [[Refraction]]
* [[Total internal reflection]]
* [[Evanescent wave]]

==References==

<references />

== External links ==

* [http://mintaka.sdsu.edu/GF/explain/optics/discovery.html Discovery of the law of refraction]

[[Category:Geometrical optics]]
[[Category:Introductory physics]]
[[Category:Eponymous laws]]

[[cs:Snellův zákon]]
[[de:Snelliussches Brechungsgesetz]]
[[es:Ley de Snell]]
[[fr:Lois de Snell-Descartes]]
[[it:Legge di Snell]]
[[he:חוק סנל]]
[[nl:Wet van Snellius]]
[[ja:スネルの法則]]
[[no:Snells brytningslov]]
[[pl:Prawo Snelliusa]]
[[ru:Закон Снелла]]
[[sl:Lomni zakon]]
[[sv:Snells lag]]
[[zh:光的折射定律]]

Snell's law

2007-01-21T18:20:41Z

JSpudeman: No offense, but i think continual prose is better than segmented paragraphs. The intro is around the same size if not smaller now, and has practically the same information.Also.. please.. rm large img

[[Image:Snells law.svg|thumb|300px|[[Refraction]] of light at the interface between two media of different [[refractive index|refractive indices]], with n2 > n1. Since the velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.]]

In [[optics]] and [[physics]], '''Snell's law''' (also known as '''Descartes' Law''' or the '''law of refraction'''), is a [[mathematical formula|formula]] used in [[ray tracing]] and [[theory]] to describe the relationship between the angles of incidence and refraction, when referring to light or other [[wave]]s, passing through a boundary between two different [[isotropic]] [[medium (optics)|media]], such as air and glass.

Named for one of it's discoverers, [[Willebrord Snellius]], the law states that the ratio of the [[sine]]s of the angles of incidence and refraction are a constant value, depending upon the media, which is also obtained through the ratio of [[velocities]] in the two media, or equivalently, the inverse ratio of the indices of refraction:

{| cellspacing="10"
|<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{n_2}{n_1}</math>
| or
|<math>n_1\sin\theta_1 = n_2\sin\theta_2\ </math>
|}

Snell's law follows from [[Fermat]]'s [[Fermat's principle|principle of least time]], which in turn follows from the propagation of light as waves.
== History ==
[[Image:Snell Law of Sines 1837.png|thumb|right|300px|An 1837 view of the history of "the Law of the Sines"<ref>William Whewell, ''History of the Inductive Science from the Earliest to the Present Times'', London: John H. Parker, 1837.</ref>]]
Snell's law was first discovered and described by [[Ibn Sahl]] in a manuscript written c.[[984]],<ref>{{cite journal | author=Rashed, Roshdi | title= A pioneer in anaclastics: Ibn Sahl on burning mirrors and lenses | journal= [[Isis (journal)|Isis]]| year= 1990| volume= 81| pages= 464–491 |doi=10.1086/355456}}</ref> who used it to work out the shapes of lenses that focus light with no geometric aberrations, known as [[anaclastic lens]]es. It was discovered again by [[Thomas Harriot]] in [[1602]],<ref>{{cite journal | author=Kwan, A., Dudley, J., and Lantz, E. | title=Who really discovered Snell's law? | journal=[[Physics World]] | year=2002 | volume=15 | issue=4 | pages=64 |url=http://physicsworldarchive.iop.org/index.cfm?action=summary&doc=15%2F4%2Fphwv15i4a44%40pwa-xml&qt=}}</ref> who did not publish his work.

In [[1621]], it was discovered yet again by Willebrord Snel, in a mathematically equivalent form, but unpublished during his lifetime. [[René Descartes]] independently derived the law using heuristic momentum conservation arguments in terms of sines in his [[1637]] treatise ''[[Discourse on Method]]'' (though detractors such as Fermat accused Descartes of working toward the already known answer with sophistic reasoning), and used it to solve a range of optical problems. Rejecting Descartes' solution, Pierre de Fermat arrived at the same solution based solely on his principle of least time.

In [[French language|French]], Snell's Law is called "la loi de Descartes" or "loi de Snell-Descartes."

[[Image:Huygens Refracted Waves.png|left|thumb|125px|Huygens's construction]]

In his 1678 ''Traité de la Lumiere'', [[Christiaan Huygens]] showed how Snell's law of sines could be explained by, or derived from, the wave nature of light, using what we have come to call the [[Huygens–Fresnel principle]].

== Explanation ==
Snell's law is used to determine the direction of light rays though refractive media with varying indices of refraction. The indices of refraction of the media, labeled <math>n_1,n_2</math> and so on, are used to represent the factor by which light is "slowed down" within a refractive medium, such as glass or water, compared to its velocity in a vacuum.

As light passes the border between media, depending upon the relative refractive indices of the two media, the light will either be refracted to a lesser angle, or a greater one. These angles are measured with respect to the ''normal line'', represented perpendicular to the boundary. In the case of light traveling from air into water, light would be refracted towards the normal line, due to the fact that the light is slowed down in water; light traveling from water to air would refract away from the normal line.

Refraction between two surfaces is also referred to as ''reversible'' due to the fact that if all conditions were identical, the angles would be the same for light propagating in the opposite direction.

Snell's law is only generally true for isotropic or specular media (such as [[glass]]). In [[anisotropic]] media such as some [[crystal]]s, [[birefringence]] may split the refracted ray into two rays, the ''ordinary'' or ''o''-ray which follows Snell's law, and the other ''extraordinary'' or ''e''-ray which may not be co-planar with the incident ray.

When the light or other wave involved is monochromatic, that is, of a single frequency, Snell's law can also be expressed in terms of a ratio of wavelengths in the two media, λ1 and λ2:

:<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{\lambda_1}{\lambda_2}</math>

=== Total internal reflection and critical angle ===
[[Image:Refraction internal reflection diagram.PNG|thumb|220px|right|An example of the angles involved within total internal reflection.]]
When light moves from a dense to a less dense medium, such as from water to air, Snell's law cannot be used to calculate the refracted angle when the resolved sine value is higher than 1. At this point, light is reflected in the incident medium, known as internal reflection. Before the ray totally internally reflects, the light refracts at the '''critical angle'''; it travels directly along the surface between the two refractive media, without a change in phases like in other forms of optical phenomena.

As an example, a ray of light is incident at <math>50^o</math> towards a water–air boundary. If the angle is calculated using Snell's Law, then the resulting sine value will not invert, and thus the refracted angle cannot be calculated:

:<math>\theta_2 = \sin^{-1} (\frac{n_1}{n_2}\sin\theta_1) = \sin^{-1} (\frac{1.333}{1.000}0.766) = \sin^{-1} 1.021</math>

Snell's Law cannot calculate such angles because there is no refracted outgoing ray.

In order to calculate the critical angle, let <math>\theta_2 = 90^o</math> and solve for <math>\theta_\mathrm{crit}</math>:

:<math>\theta_{\mathrm{crit}} = \sin^{-1} \left( \frac{n_2}{n_1} \right)</math>

When θ1 > θcrit, no refracted ray appears, and the incident ray undergoes [[total internal reflection]] from the interface medium.

=== Derivations ===
Snell's law may be derived from [[Fermat's principle]], which states that the light travels the path which takes the least time. By taking the [[derivative]] of the [[optical path length]], the [[stationary point]] is found giving the path taken by the light (though it should be noted that the result does not show light taking the least time path, but rather one that is stationary with respect to small variations as there are cases where light actually takes the greatest time path, as in a spherical mirror).

Alternatively, Snell's law can be derived using interference of all possible paths of light wave from source to observer—it results in destructive interference everywhere except extrema of phase (where interference is constructive)—which become actual paths. In a classic analogy by [[Richard Feynman]], the area of lower refractive index is replaced by a beach, the area of higher refractive index by the sea, and the fastest way for a rescuer on the beach to get to a [[drowning]] person in the sea is to run along a path that follows Snell's law.

Another way to derive Snell’s Law involves an application of the general [[boundary conditions]] of [[Maxwell equations]] for [[electromagnetic radiation]].

== Uses ==
=== Calculating refractive indices ===

In the diagram on the right, two media of refractive indices ''n''1 (on the left) and ''n''2 (on the right) meet at a surface or interface (vertical line). ''n''2 > ''n''1, and light has a slower [[phase velocity]] within the second medium.

A light ray '''PO''' in the leftmost medium strikes the interface at the point '''O'''. From point '''O''', we project a straight line at right angles to the line of the interface; this is known as the [[Surface normal|normal]] to the surface (horizontal line). The angle between the normal and the light ray '''PO''' is known as the ''angle of incidence'', θ1.

The ray continues through the interface into the medium on the right; this is shown as the ray '''OQ'''. The angle it makes to the normal is known as the ''angle of refraction'', θ2.

:<math>n_1 \sin\theta_1 = n_2 \sin\theta_2 </math> or <math>\sum_{k=x,y}^N x=n_x\sin\theta_x,n_y \sin\theta_y</math>
:<math>\frac{n_1}{n_2} = \frac{\sin\theta_2}{\sin\theta_1}</math>
Note that, for the case of θ1 = 0° (i.e., a ray perpendicular to the interface) the solution is θ2 = 0° regardless of the values of ''n''1 and ''n''2-- a ray entering a medium perpendicular to the surface is never bent.

The above is also valid for light going from a dense to a less dense medium; the symmetry of Snell's law shows that the same ray paths are applicable in opposite direction.

A qualitative rule for determining the direction of refraction is that the ray in the denser medium is always closer to the normal. An analogy often used to remember this is done by visualizing the ray as a car crossing the boundary between asphalt (the less dense medium) and mud (the denser medium). Depending on the angle, either the left wheel or the right wheel of the car will cross into the new medium first, causing the car to swerve.

=== Vector form ===

Given a normalized ray vector '''v''' and a normalized plane normal vector '''p''', one can work out the normalized reflected and refracted rays:

:<math>\cos\theta_1=\mathbf{v}\cdot\mathbf{p}</math>
:<math>\cos\theta_2=\sqrt{1-\left(\frac{n_1}{n_2}\right)^2\left(1-\left(\cos\theta_1\right)^2\right)}</math>
:<math>\mathbf{v}_{\mathrm{reflect}}=\mathbf{v}-\left(2\cos\theta_1\right)\mathbf{p}</math>
:<math>\mathbf{v}_{\mathrm{refract}}=\left(\frac{n_1}{n_2}\right)\mathbf{v} + \left(\cos\theta_2 - \frac{n_1}{n_2}\cos\theta_1\right)\mathbf{p}</math>
Note: <math>\mathbf{v}\cdot\mathbf{p}</math> must be positive.

The cosines may be recycled and used in the [[Fresnel equations]] for working out the intensity of the resulting rays. During total internal reflection an [[evanescent wave]] is produced, which [[exponential decay|rapidly decays]] from the surface into the second medium. Conservation of energy is maintained by the circulation of energy across the boundary, averaging to zero net energy transmission.

==Dispersion==

In many wave-propagation media, wave velocity changes with frequency or wavelength of the waves; this is true of light propagation in most transparent substances other than a vacuum. These media are called dispersive. The result is that the angles determined by Snell's law also depend on frequency or wavelength, so that a ray of mixed wavelengths, such as white light, will spread or disperse. Such dispersion of light in glass or water underlies the origin of [[rainbow]]s, since different wavelenghts appear as different colors.

In optical instruments, [[dispersion (optics)|dispersion]] leads to [[chromatic aberration]], a color-dependent blurring that sometimes is the resolution-limiting effect. This was especially true in [[refracting telescope]]s, before the invention of achromatic objective lenses.

==See also==

* [[Fresnel equations]]
* [[Reflection (physics)|Reflection]]
* [[Refraction]]
* [[Total internal reflection]]
* [[Evanescent wave]]

==References==

<references />

== External links ==

* [http://mintaka.sdsu.edu/GF/explain/optics/discovery.html Discovery of the law of refraction]

[[Category:Geometrical optics]]
[[Category:Introductory physics]]
[[Category:Eponymous laws]]

[[cs:Snellův zákon]]
[[de:Snelliussches Brechungsgesetz]]
[[es:Ley de Snell]]
[[fr:Lois de Snell-Descartes]]
[[it:Legge di Snell]]
[[he:חוק סנל]]
[[nl:Wet van Snellius]]
[[ja:スネルの法則]]
[[no:Snells brytningslov]]
[[pl:Prawo Snelliusa]]
[[ru:Закон Снелла]]
[[sl:Lomni zakon]]
[[sv:Snells lag]]
[[zh:光的折射定律]]

Fresnel diffraction

2007-01-20T22:03:03Z

JSpudeman: Cleared up intro -- ambiguity

[[Image:Diffraction geometry.svg|thumb|350px|Diffraction geometry, showing aperture (or diffracting object) plane and image plane, with coordinate system]]
In [[optics]], '''Fresnel diffraction''' or '''near-field diffraction''' is a process of diffraction which occurs when a wave passes through an [[aperture]] and diffracts in the near field, causing any diffraction pattern observed to differ in size and shape, relative to the distance. It occurs due to the short distance in which the diffracted waves propogate, which results in a [[fresnel number]] less than 1 (<math>F \lesssim 1</math>). When the distance is increased, outgoing diffracted waves become [[planar]] and [[Fraunhofer diffraction]] occurs.

==The Fresnel diffraction integral==

The electric field [[diffraction]] pattern at a point ''(x,y,z)'' is given by:

:<math> E(x,y,z)=-{i \over \lambda} \iint{ E(x',y',0) \frac{e^{ikr}}{r} \cos \theta}dx'dy' </math>

where

:<math> r=\sqrt{(x-x')^2+(y-y')^2+z^2} </math>

:<math> i \,</math> is the [[imaginary unit]],

and

:<math>\cos \theta = \frac{z}{r}</math> is the cosine of the angle between ''z'' and ''r''.

Analytical solution of this integral is impossible for all but the simplest diffraction geometries. Therefore, it is usually calculated numerically.

===The Fresnel approximation===
The main problem for solving the integral is the expression of ''r''. First, we can simplify the algebra by introducing the substitution:

:<math>\rho^2 = (x-x')^2+(y-y')^2 \,</math>

Substituting into the expression for ''r'', we find:

:<math> r= \sqrt{\rho^2+z^2} = z \sqrt{ 1 + \frac{\rho^2}{z^2} } </math>

Next, using the [[Taylor series]] expansion

:<math>\sqrt{1+u} = (1+u)^{1/2} = 1 + \frac{u}{2} - \frac{u^2}{8} + \dots</math>

we can express ''r'' as

:<math>r = z \sqrt{ 1 + \frac{\rho^2}{z^2} } </math>
::<math> = z \left[ 1 + \frac{\rho^2}{2 z^2} - \frac{1}{8} \left( \frac{\rho^2}{z^2} \right)^2 + \dots \right] </math>
::<math> = z + \frac{\rho^2}{2 z} - \frac{\rho^4}{8z^3} + \dots</math>

If we consider all the terms of Taylor series there is no approximation.<ref>There was actually an approximation in a prior step, when assuming <math>e^{i k r}/r</math> is a real wave. In fact this is not a real solution to the vector [[Helmholtz_equation|Helmholtz equation]], but to the scalar one. See [[scalar_wave_approximation|scalar wave approximation]]</ref>. Let us substitute this expression in the argument of the exponential within the integral; the key to the Fresnel approximation is to assume that the third element is very small and can be ignored. In order to make this possible, it has to contribute to the variation of the exponential for an almost null term. In other words, it has to be much smaller than the period of the complex exponential, i.e. <math>2 \pi</math>:

:<math> k \frac{\rho^4}{8 z^3} \ll 2 \pi</math>

expressing ''k'' in terms of the wavelength,

:<math>k = { 2 \pi \over \lambda } \,</math>

we get the following relationship:

:<math> \frac{\rho^4}{z^3 \lambda} \ll 8</math>

Multiplying both sides by <math>z/\lambda</math>, we have

:<math> \frac{\rho^4}{z^2 \lambda^2} \ll 8 {z \over \lambda}</math>

or, substituting the earlier expression for ρ2 ,

:<math> \frac{[(x-x')^2+(y-y')^2]^2}{z^2 \lambda^2} \ll 8 {z \over \lambda}</math>

If this condition holds true for all values of ''x'', ''x' '', ''y'' and ''y' '', then we can ignore the third term in the Taylor expression. Furthermore, if the third term is negligible, then all terms of higher order will be even smaller, so we can ignore them as well. We can then approximate the expression with only the first two terms:

:<math> r \approx z + \frac{(x-x')^2 +(y-y')^2}{2 z} </math>

This equation, then, is the '''Fresnel approximation''', and the inequality stated above is a condition for approximation's validity.

===Fresnel Diffraction===

The condition for validity is fairly weak, and it allows all length parameters to take comparable values, provided the aperture is small compared to the path length. Moreover, if we are interested in the behaviour of the field only in a small area close to the origin, i.e. for values of ''x'' and ''y'' much smaller than ''z'', then we can assume <math>\theta \approx 0</math>, that means <math>\cos \theta \approx 1</math> and the ''r'' in the denominator of the Fresnel integral can be approximated by <math>r \approx z</math>.

Unlike [[Fraunhofer diffraction]], Fresnel diffraction has to account for the curvature of the [[wavefront]], in order to correctly calculate relative [[Phase (waves)|phase]] of interfering waves.

For Fresnel diffraction the electric field at point ''(x,y,z)'' is given by:

:<math> E(x,y,z)=-{i \over \lambda}{e^{ikz} \over z}\iint E(x',y',0)e^{{ik \over 2z}[(x-x')^2+(y-y')^2]}dx'dy' </math>

This is the Fresnel diffraction integral; it means that, if the Fresnel approximation is valid, the propagating field is a spherical wave, originating at the aperture and moving along ''z''. The integral modulates the amplitude and phase of the spherical wave.
Analytical solution of this expression is still only possible in rare cases. For a further simplified case, valid only much larger distances from the diffraction source see [[Fraunhofer diffraction]].

==Alternative forms==

===Convolution===
The integral can be expressed in other ways in order to calculate it using some mathematical properties. If we define the following function:

:<math>h(x,y) = \frac{e^{i k z}}{i \lambda z} e^{i \frac{k}{2 z} (x^2 + y^2)}</math>

then the integral can be expressed in terms of a [[convolution]]:

:<math>E(x,y,z) = E(x,y,0) * h (x,y) \, </math>

it other words we are representing the propagation using a linear-filter modeling. That is why we might call the function ''h(x,y)'' the impulse response of free space propagation.

===Fourier Transform===

Another possible way is through the [[Fourier transform]]. If in the integral we express ''k'' in terms of the wavelength,

:<math>k = { 2\pi \over \lambda } </math>

and we expand each component of the transverse displacement,
:<math>(x-x')^2 = x^2 + x'^2 -2 x x' \,</math>
:<math>(y-y')^2 = y^2 + y'^2 -2 y y' \,</math>
then we can express the integral in terms of the two dimensional Fourier transform. Let us use the following definition:

:<math>G(p,q) = \mathcal{F} \left\{ g(x,y) \right\} \equiv \iint_{-\infty}^{\infty} g(x,y) e^{-i 2 \pi (p x + q y)} dx dy </math>

where ''p'' and ''q'' are spatial frequencies (in units of lines/meter). The Fresnel integral can be expressed as:

:<math>E(x,y,z) = \frac{e^{i k z}}{i \lambda z} e^{i \frac{\pi}{\lambda z}(x^2 + y^2)} \mathcal{F}
\left. \left\{ E(x,y,0) e^{i \frac{\pi}{\lambda z} (x^2 + y^2)} \right\} \right|_{p = \frac{x}{\lambda z}; q = \frac{y}{\lambda z}}
</math>

:::::<math>= H(p,q) \cdot G(p,q) |_{p = {x \over \lambda z} , q = { y \over \lambda z } }</math>

where
:<math>H(p,q) = \mathcal{F} \left\{ h(x,y) \right\} </math>

i.e. first multiply the field to be propagated for a complex exponential, calculate its two dimensional Fourier transform, replace ''(p,q)'' with <math>\left( \frac{x}{\lambda z}, \frac{y}{\lambda z} \right)</math> and multiply it for another factor. This expression is better than the others when the process leads to a known Fourier transform.

==See also==
* [[Fraunhofer diffraction]]
* [[Fresnel integral]]
* [[Fresnel zone]]
* [[Fresnel number]]
* [[Augustin-Jean Fresnel]]

[[Category:Diffraction]]

==Notes==
<references/>

[[es:Difracción de Fresnel]]
[[ja:フレネル回折]]

Fresnel diffraction

2007-01-20T21:41:47Z

JSpudeman: There's some inadequacies in the terminology used here.. when the fresnel number is too high, then fraunhofer diffraction occurs. Needs to be rephrased.

'''Fresnel diffraction''' or '''near-field diffraction''' is the [[diffraction]] pattern of an [[electromagnetic wave]] obtained close to the diffracting object (often a source or [[aperture]]). More accurately, it is the diffraction case when the [[Fresnel number]] is large enough to facilitate fresnel diffraction -- [[Fraunhofer diffraction|Fraunhofer approximation]] (diffraction of parallel beams) can not be used.

[[Image:Diffraction geometry.svg|thumb|350px|Diffraction geometry, showing aperture (or diffracting object) plane and image plane, with coordinate system]]

==The Fresnel diffraction integral==

The electric field [[diffraction]] pattern at a point ''(x,y,z)'' is given by:

:<math> E(x,y,z)=-{i \over \lambda} \iint{ E(x',y',0) \frac{e^{ikr}}{r} \cos \theta}dx'dy' </math>

where

:<math> r=\sqrt{(x-x')^2+(y-y')^2+z^2} </math>

:<math> i \,</math> is the [[imaginary unit]],

and

:<math>\cos \theta = \frac{z}{r}</math> is the cosine of the angle between ''z'' and ''r''.

Analytical solution of this integral is impossible for all but the simplest diffraction geometries. Therefore, it is usually calculated numerically.

===The Fresnel approximation===
The main problem for solving the integral is the expression of ''r''. First, we can simplify the algebra by introducing the substitution:

:<math>\rho^2 = (x-x')^2+(y-y')^2 \,</math>

Substituting into the expression for ''r'', we find:

:<math> r= \sqrt{\rho^2+z^2} = z \sqrt{ 1 + \frac{\rho^2}{z^2} } </math>

Next, using the [[Taylor series]] expansion

:<math>\sqrt{1+u} = (1+u)^{1/2} = 1 + \frac{u}{2} - \frac{u^2}{8} + \dots</math>

we can express ''r'' as

:<math>r = z \sqrt{ 1 + \frac{\rho^2}{z^2} } </math>
::<math> = z \left[ 1 + \frac{\rho^2}{2 z^2} - \frac{1}{8} \left( \frac{\rho^2}{z^2} \right)^2 + \dots \right] </math>
::<math> = z + \frac{\rho^2}{2 z} - \frac{\rho^4}{8z^3} + \dots</math>

If we consider all the terms of Taylor series there is no approximation.<ref>There was actually an approximation in a prior step, when assuming <math>e^{i k r}/r</math> is a real wave. In fact this is not a real solution to the vector [[Helmholtz_equation|Helmholtz equation]], but to the scalar one. See [[scalar_wave_approximation|scalar wave approximation]]</ref>. Let us substitute this expression in the argument of the exponential within the integral; the key to the Fresnel approximation is to assume that the third element is very small and can be ignored. In order to make this possible, it has to contribute to the variation of the exponential for an almost null term. In other words, it has to be much smaller than the period of the complex exponential, i.e. <math>2 \pi</math>:

:<math> k \frac{\rho^4}{8 z^3} \ll 2 \pi</math>

expressing ''k'' in terms of the wavelength,

:<math>k = { 2 \pi \over \lambda } \,</math>

we get the following relationship:

:<math> \frac{\rho^4}{z^3 \lambda} \ll 8</math>

Multiplying both sides by <math>z/\lambda</math>, we have

:<math> \frac{\rho^4}{z^2 \lambda^2} \ll 8 {z \over \lambda}</math>

or, substituting the earlier expression for ρ2 ,

:<math> \frac{[(x-x')^2+(y-y')^2]^2}{z^2 \lambda^2} \ll 8 {z \over \lambda}</math>

If this condition holds true for all values of ''x'', ''x' '', ''y'' and ''y' '', then we can ignore the third term in the Taylor expression. Furthermore, if the third term is negligible, then all terms of higher order will be even smaller, so we can ignore them as well. We can then approximate the expression with only the first two terms:

:<math> r \approx z + \frac{(x-x')^2 +(y-y')^2}{2 z} </math>

This equation, then, is the '''Fresnel approximation''', and the inequality stated above is a condition for approximation's validity.

===Fresnel Diffraction===

The condition for validity is fairly weak, and it allows all length parameters to take comparable values, provided the aperture is small compared to the path length. Moreover, if we are interested in the behaviour of the field only in a small area close to the origin, i.e. for values of ''x'' and ''y'' much smaller than ''z'', then we can assume <math>\theta \approx 0</math>, that means <math>\cos \theta \approx 1</math> and the ''r'' in the denominator of the Fresnel integral can be approximated by <math>r \approx z</math>.

Unlike [[Fraunhofer diffraction]], Fresnel diffraction has to account for the curvature of the [[wavefront]], in order to correctly calculate relative [[Phase (waves)|phase]] of interfering waves.

For Fresnel diffraction the electric field at point ''(x,y,z)'' is given by:

:<math> E(x,y,z)=-{i \over \lambda}{e^{ikz} \over z}\iint E(x',y',0)e^{{ik \over 2z}[(x-x')^2+(y-y')^2]}dx'dy' </math>

This is the Fresnel diffraction integral; it means that, if the Fresnel approximation is valid, the propagating field is a spherical wave, originating at the aperture and moving along ''z''. The integral modulates the amplitude and phase of the spherical wave.
Analytical solution of this expression is still only possible in rare cases. For a further simplified case, valid only much larger distances from the diffraction source see [[Fraunhofer diffraction]].

==Alternative forms==

===Convolution===
The integral can be expressed in other ways in order to calculate it using some mathematical properties. If we define the following function:

:<math>h(x,y) = \frac{e^{i k z}}{i \lambda z} e^{i \frac{k}{2 z} (x^2 + y^2)}</math>

then the integral can be expressed in terms of a [[convolution]]:

:<math>E(x,y,z) = E(x,y,0) * h (x,y) \, </math>

it other words we are representing the propagation using a linear-filter modeling. That is why we might call the function ''h(x,y)'' the impulse response of free space propagation.

===Fourier Transform===

Another possible way is through the [[Fourier transform]]. If in the integral we express ''k'' in terms of the wavelength,

:<math>k = { 2\pi \over \lambda } </math>

and we expand each component of the transverse displacement,
:<math>(x-x')^2 = x^2 + x'^2 -2 x x' \,</math>
:<math>(y-y')^2 = y^2 + y'^2 -2 y y' \,</math>
then we can express the integral in terms of the two dimensional Fourier transform. Let us use the following definition:

:<math>G(p,q) = \mathcal{F} \left\{ g(x,y) \right\} \equiv \iint_{-\infty}^{\infty} g(x,y) e^{-i 2 \pi (p x + q y)} dx dy </math>

where ''p'' and ''q'' are spatial frequencies (in units of lines/meter). The Fresnel integral can be expressed as:

:<math>E(x,y,z) = \frac{e^{i k z}}{i \lambda z} e^{i \frac{\pi}{\lambda z}(x^2 + y^2)} \mathcal{F}
\left. \left\{ E(x,y,0) e^{i \frac{\pi}{\lambda z} (x^2 + y^2)} \right\} \right|_{p = \frac{x}{\lambda z}; q = \frac{y}{\lambda z}}
</math>

:::::<math>= H(p,q) \cdot G(p,q) |_{p = {x \over \lambda z} , q = { y \over \lambda z } }</math>

where
:<math>H(p,q) = \mathcal{F} \left\{ h(x,y) \right\} </math>

i.e. first multiply the field to be propagated for a complex exponential, calculate its two dimensional Fourier transform, replace ''(p,q)'' with <math>\left( \frac{x}{\lambda z}, \frac{y}{\lambda z} \right)</math> and multiply it for another factor. This expression is better than the others when the process leads to a known Fourier transform.

==See also==
* [[Fraunhofer diffraction]]
* [[Fresnel integral]]
* [[Fresnel zone]]
* [[Fresnel number]]
* [[Augustin-Jean Fresnel]]

[[Category:Diffraction]]

==Notes==
<references/>

[[es:Difracción de Fresnel]]
[[ja:フレネル回折]]

Talk:Fraunhofer diffraction

2007-01-19T00:53:37Z

JSpudeman: Changed class

Fraunhofer diffraction

2007-01-19T00:50:51Z

JSpudeman: Expanded references a bit

In [[optics]], '''Fraunhofer diffraction''' is a form of wave [[diffraction]], which occurs when field waves are passed through an [[aperture]] or slit, causing the size of an observed aperture image to change<ref name="Hecht_optics_p396">''Hecht, E. (1987)'', p396 -- Definition of Frauenhoffer diffraction and explanation of forms.</ref><ref name="Hecht_optics_p397">''Hecht, E. (1987)'', p397 -- diagram and explanation of frauenhoffer diffraction with reference to an opaque shield w/ aperture.</ref> due to the far-field location of observation and differing amplitudes of outgoing waves passing through the aperture. It is used alongside [[fresnel diffraction]], in which, both the size and shape of the observed aperture image is changed, relative to the distance of observation<ref name="Hecht_optics_p396" /> -- in Frauenhofer diffraction, only the size of the aperture image changes due to the increase in the distance between the aperture and the observation point exceeding that defined as fresnel diffraction (<math>F \gg 1</math>).<ref name="Hecht_optics_p397" />

== Explanation ==
For an aperture with an amplitude transmittance <math>f(x)</math> on which plane waves are incident, the diffracted far-field amplitude as a function of the angle <math>\theta</math> with the propagation direction of the incident waves is
:<math>\psi(\theta) \propto \int_{-\infty}^{\infty} f(x) e^{i(k\theta)x} dx,</math> where <math>k=2\pi/\lambda</math> is the [[wavenumber#In wave equations|circular wavenumber]] of the incident waves. The expression is the Fourier transform of the aperture function against the variable <math>k\theta</math>. This approximation is only valid for small values of <math>\theta</math>. Note that the aperture function acts on the ''amplitude'', not on the intensity (amplitude squared) of the waves. It can be complex-valued to indicate a phase shift.

== Forms ==
=== Aperture form ===
A [[far-field]] pattern exists at distances that are large compared with ''s'' 2/λ, where ''s'' is a characteristic dimension of the source and λ is the [[wavelength]]. For example, if the source is a uniformly illuminated circle, then ''s'' is the radius of the circle.

The far-field diffraction pattern of a source may also be observed (except for scale) in the focal plane of a well-corrected lens. The far-field pattern of a diffracting [[screen]] illuminated by a [[wikt:point source|point source]] may be observed in the image plane of the source.

If a light source and an observation screen are effectively far enough from a diffraction aperture (for example a slit), then the [[wavefront]]s arriving at the aperture and the screen can be considered to be [[Collimated light|collimated]], or ''[[plane waves|plane]]''. [[Fresnel diffraction]], or ''near-field diffraction'' occurs when this is not the case and the curvature of the incident wavefronts is taken into account.

In far-field diffraction, if the observation screen is moved relative to the aperture, the diffraction pattern produced changes uniformly in size. This is not the case in near-field diffraction, where the diffraction pattern changes both in size and shape.

=== Slit form===
Fraunhofer diffraction through a slit can be achieved with two lenses and a screen. Using a point-like source for light and a [[collimating lens]] it is possible to make parallel light, which will then be passed through the slit. After the slit there is another lens that will focus the parallel light onto a screen for observation. The same setup with multiple slits can also be used, creating a different diffraction pattern.

Since this type of diffraction is mathematically simple, this experimental setup can be used to find the wavelength of the incident [[monochromatic]] light with high accuracy.

==Examples==

===Diffraction from a slit===

The simplest example is Fraunhofer diffraction from a slit, i.e. <math>f(x) = 1</math> for <math>-a/2 < x < a/2</math> and <math>f(x)=0</math> elsewhere. In this case,
:<math>\psi(\theta) = \mathrm{sinc}(\pi a \theta/\lambda),</math>
The [[sinc|unnormalized sinc]] function peaks at <math>\theta=0</math> and has zeroes at <math>\theta=\pm n\lambda/a</math>, where <math>n=1, 2, \ldots</math>.

===Gaussian profile===

An aperture with a Gaussian profile <math>f(x) = \exp(-ax^2)</math> results in
:<math>\psi(\theta) = \exp\left(\frac{-k^2\theta^2}{4a}\right) .</math>
For example, if a laser beam has an intensity profile with a full width at half maximum (FWHM) <math>W</math>, then <math>a=2\ln 2/W^2</math>. At a wavelength <math>\lambda</math>, the amplitude profile is
:<math>\psi(\theta) = \exp\left(-\frac{\pi^2W^2}{2 \lambda^2\ln 2}\theta^2\right),</math>
i.e. an angular FWHM in the intensity of <math>2\lambda\ln 2/\pi W \approx 0.44\lambda/W</math>.

==References==
=== Notes ===
<references />

=== Book references ===
* {{cite book|author=Hecht, E.|title=Optics, 2nd edition|publisher=Addison Wesley|year=1987|id=ISBN 0-201-11611-1}}
*{{cite book|author=Jenkins, F., White, H.|title=Fundamentals of Optics, 4th edition|publisher=McGraw-Hill INC.|year=1976|id=ISBN 0-07-032330-5}}

== See also ==
*[[Fresnel diffraction]]
*[[Fresnel number]]
*[[Huygens Principle]]

== External links ==
* [http://scienceworld.wolfram.com/physics/FraunhoferDiffraction.html Fraunhofer diffraction] on [[ScienceWorld]]
* [http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fraunhofcon.html Fraunhofer diffraction] on [[HyperPhysics]]

[[Category:Diffraction]]
[[Category:Physics]]
[[Category:Optics]]
[[ja:フラウンホーファー回折]]

Fraunhofer diffraction

2007-01-19T00:48:52Z

JSpudeman: Another fixup of layout

In [[optics]], '''Fraunhofer diffraction''' is a form of wave [[diffraction]], which occurs when field waves are passed through an [[aperture]] or slit, causing the size of an observed aperture image to change<ref name="Hecht_optics_p396">Hecht, E. (1987), p396</ref><ref name="Hecht_optics_p397">Hecht, E. (1987), p397</ref> due to the far-field location of observation and differing amplitudes of outgoing waves passing through the aperture. It is used alongside [[fresnel diffraction]], in which, both the size and shape of the observed aperture image is changed, relative to the distance of observation<ref name="Hecht_optics_p396" /> -- in Frauenhofer diffraction, only the size of the aperture image changes due to the increase in the distance between the aperture and the observation point exceeding that defined as fresnel diffraction (<math>F \gg 1</math>).<ref name="Hecht_optics_p397" />

== Explanation ==
For an aperture with an amplitude transmittance <math>f(x)</math> on which plane waves are incident, the diffracted far-field amplitude as a function of the angle <math>\theta</math> with the propagation direction of the incident waves is
:<math>\psi(\theta) \propto \int_{-\infty}^{\infty} f(x) e^{i(k\theta)x} dx,</math> where <math>k=2\pi/\lambda</math> is the [[wavenumber#In wave equations|circular wavenumber]] of the incident waves. The expression is the Fourier transform of the aperture function against the variable <math>k\theta</math>. This approximation is only valid for small values of <math>\theta</math>. Note that the aperture function acts on the ''amplitude'', not on the intensity (amplitude squared) of the waves. It can be complex-valued to indicate a phase shift.

== Forms ==
=== Aperture form ===
A [[far-field]] pattern exists at distances that are large compared with ''s'' 2/λ, where ''s'' is a characteristic dimension of the source and λ is the [[wavelength]]. For example, if the source is a uniformly illuminated circle, then ''s'' is the radius of the circle.

The far-field diffraction pattern of a source may also be observed (except for scale) in the focal plane of a well-corrected lens. The far-field pattern of a diffracting [[screen]] illuminated by a [[wikt:point source|point source]] may be observed in the image plane of the source.

If a light source and an observation screen are effectively far enough from a diffraction aperture (for example a slit), then the [[wavefront]]s arriving at the aperture and the screen can be considered to be [[Collimated light|collimated]], or ''[[plane waves|plane]]''. [[Fresnel diffraction]], or ''near-field diffraction'' occurs when this is not the case and the curvature of the incident wavefronts is taken into account.

In far-field diffraction, if the observation screen is moved relative to the aperture, the diffraction pattern produced changes uniformly in size. This is not the case in near-field diffraction, where the diffraction pattern changes both in size and shape.

=== Slit form===
Fraunhofer diffraction through a slit can be achieved with two lenses and a screen. Using a point-like source for light and a [[collimating lens]] it is possible to make parallel light, which will then be passed through the slit. After the slit there is another lens that will focus the parallel light onto a screen for observation. The same setup with multiple slits can also be used, creating a different diffraction pattern.

Since this type of diffraction is mathematically simple, this experimental setup can be used to find the wavelength of the incident [[monochromatic]] light with high accuracy.

==Examples==

===Diffraction from a slit===

The simplest example is Fraunhofer diffraction from a slit, i.e. <math>f(x) = 1</math> for <math>-a/2 < x < a/2</math> and <math>f(x)=0</math> elsewhere. In this case,
:<math>\psi(\theta) = \mathrm{sinc}(\pi a \theta/\lambda),</math>
The [[sinc|unnormalized sinc]] function peaks at <math>\theta=0</math> and has zeroes at <math>\theta=\pm n\lambda/a</math>, where <math>n=1, 2, \ldots</math>.

===Gaussian profile===

An aperture with a Gaussian profile <math>f(x) = \exp(-ax^2)</math> results in
:<math>\psi(\theta) = \exp\left(\frac{-k^2\theta^2}{4a}\right) .</math>
For example, if a laser beam has an intensity profile with a full width at half maximum (FWHM) <math>W</math>, then <math>a=2\ln 2/W^2</math>. At a wavelength <math>\lambda</math>, the amplitude profile is
:<math>\psi(\theta) = \exp\left(-\frac{\pi^2W^2}{2 \lambda^2\ln 2}\theta^2\right),</math>
i.e. an angular FWHM in the intensity of <math>2\lambda\ln 2/\pi W \approx 0.44\lambda/W</math>.

==References==
=== Notes ===
<references />

=== Book references ===
* {{cite book|author=Hecht, E.|title=Optics, 2nd edition|publisher=Addison Wesley|year=1987|id=ISBN 0-201-11611-1}}
*{{cite book|author=Jenkins, F., White, H.|title=Fundamentals of Optics, 4th edition|publisher=McGraw-Hill INC.|year=1976|id=ISBN 0-07-032330-5}}

== See also ==
*[[Fresnel diffraction]]
*[[Fresnel number]]
*[[Huygens Principle]]

== External links ==
* [http://scienceworld.wolfram.com/physics/FraunhoferDiffraction.html Fraunhofer diffraction] on [[ScienceWorld]]
* [http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fraunhofcon.html Fraunhofer diffraction] on [[HyperPhysics]]

[[Category:Diffraction]]
[[Category:Physics]]
[[Category:Optics]]
[[ja:フラウンホーファー回折]]

Fraunhofer diffraction

2007-01-19T00:47:43Z

JSpudeman: Added new categorisation (makes it a bit easier to find it now) ; wikified layout, tommorow i'll fix some of it up.

In [[optics]], '''Fraunhofer diffraction''' is a form of wave [[diffraction]], which occurs when field waves are passed through an [[aperture]] or slit, causing the size of an observed aperture image to change<ref name="Hecht_optics_p396">Hecht, E. (1987), p396</ref><ref name="Hecht_optics_p397">Hecht, E. (1987), p397</ref> due to the far-field location of observation and differing amplitudes of outgoing waves passing through the aperture. It is used alongside [[fresnel diffraction]], in which, both the size and shape of the observed aperture image is changed, relative to the distance of observation<ref name="Hecht_optics_p396" /> -- in Frauenhofer diffraction, only the size of the aperture image changes due to the increase in the distance between the aperture and the observation point exceeding that defined as fresnel diffraction (<math>F \gg 1</math>).<ref name="Hecht_optics_p397" />

== Explanation ==
For an aperture with an amplitude transmittance <math>f(x)</math> on which plane waves are incident, the diffracted far-field amplitude as a function of the angle <math>\theta</math> with the propagation direction of the incident waves is
:<math>\psi(\theta) \propto \int_{-\infty}^{\infty} f(x) e^{i(k\theta)x} dx,</math> where <math>k=2\pi/\lambda</math> is the [[wavenumber#In wave equations|circular wavenumber]] of the incident waves. The expression is the Fourier transform of the aperture function against the variable <math>k\theta</math>. This approximation is only valid for small values of <math>\theta</math>. Note that the aperture function acts on the ''amplitude'', not on the intensity (amplitude squared) of the waves. It can be complex-valued to indicate a phase shift.

== Forms ==
=== Aperture form ===
A [[far-field]] pattern exists at distances that are large compared with ''s'' 2/λ, where ''s'' is a characteristic dimension of the source and λ is the [[wavelength]]. For example, if the source is a uniformly illuminated circle, then ''s'' is the radius of the circle.

The far-field diffraction pattern of a source may also be observed (except for scale) in the focal plane of a well-corrected lens. The far-field pattern of a diffracting [[screen]] illuminated by a [[wikt:point source|point source]] may be observed in the image plane of the source.

If a light source and an observation screen are effectively far enough from a diffraction aperture (for example a slit), then the [[wavefront]]s arriving at the aperture and the screen can be considered to be [[Collimated light|collimated]], or ''[[plane waves|plane]]''. [[Fresnel diffraction]], or ''near-field diffraction'' occurs when this is not the case and the curvature of the incident wavefronts is taken into account.

In far-field diffraction, if the observation screen is moved relative to the aperture, the diffraction pattern produced changes uniformly in size. This is not the case in near-field diffraction, where the diffraction pattern changes both in size and shape.

==Slit form==
Fraunhofer diffraction through a slit can be achieved with two lenses and a screen. Using a point-like source for light and a [[collimating lens]] it is possible to make parallel light, which will then be passed through the slit. After the slit there is another lens that will focus the parallel light onto a screen for observation. The same setup with multiple slits can also be used, creating a different diffraction pattern.

Since this type of diffraction is mathematically simple, this experimental setup can be used to find the wavelength of the incident [[monochromatic]] light with high accuracy.

==Examples==

===Diffraction from a slit===

The simplest example is Fraunhofer diffraction from a slit, i.e. <math>f(x) = 1</math> for <math>-a/2 < x < a/2</math> and <math>f(x)=0</math> elsewhere. In this case,
:<math>\psi(\theta) = \mathrm{sinc}(\pi a \theta/\lambda),</math>
The [[sinc|unnormalized sinc]] function peaks at <math>\theta=0</math> and has zeroes at <math>\theta=\pm n\lambda/a</math>, where <math>n=1, 2, \ldots</math>.

===Gaussian profile===

An aperture with a Gaussian profile <math>f(x) = \exp(-ax^2)</math> results in
:<math>\psi(\theta) = \exp\left(\frac{-k^2\theta^2}{4a}\right) .</math>
For example, if a laser beam has an intensity profile with a full width at half maximum (FWHM) <math>W</math>, then <math>a=2\ln 2/W^2</math>. At a wavelength <math>\lambda</math>, the amplitude profile is
:<math>\psi(\theta) = \exp\left(-\frac{\pi^2W^2}{2 \lambda^2\ln 2}\theta^2\right),</math>
i.e. an angular FWHM in the intensity of <math>2\lambda\ln 2/\pi W \approx 0.44\lambda/W</math>.

== See also ==
*[[Fresnel diffraction]]
*[[Fresnel number]]
*[[Huygens Principle]]

== External links ==

* [http://scienceworld.wolfram.com/physics/FraunhoferDiffraction.html Fraunhofer diffraction] on [[ScienceWorld]]
* [http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fraunhofcon.html Fraunhofer diffraction] on [[HyperPhysics]]

==References==
=== Notes ===
<references />

=== Book references ===
* {{cite book|author=Hecht, E.|title=Optics, 2nd edition|publisher=Addison Wesley|year=1987|id=ISBN 0-201-11611-1}}
*{{cite book|author=Jenkins, F., White, H.|title=Fundamentals of Optics, 4th edition|publisher=McGraw-Hill INC.|year=1976|id=ISBN 0-07-032330-5}}

[[Category:Diffraction]]
[[Category:Physics]]
[[Category:Optics]]
[[ja:フラウンホーファー回折]]

Fraunhofer diffraction

2007-01-19T00:43:26Z

JSpudeman: Cleaned up the introduction, referenced and made it generally more concise/easy to understand.

In [[optics]], '''Fraunhofer diffraction''' is a form of wave [[diffraction]], which occurs when field waves are passed through an [[aperture]] or slit, causing the size of an observed aperture image to change<ref name="Hecht_optics_p396">Hecht, E. (1987), p396</ref><ref name="Hecht_optics_p397">Hecht, E. (1987), p397</ref> due to the far-field location of observation and differing amplitudes of outgoing waves passing through the aperture. It is used alongside [[fresnel diffraction]], in which, both the size and shape of the observed aperture image is changed, relative to the distance of observation<ref name="Hecht_optics_p396" /> -- in Frauenhofer diffraction, only the size of the aperture image changes due to the increase in the distance between the aperture and the observation point exceeding that defined as fresnel diffraction (<math>F \gg 1</math>).<ref name="Hecht_optics_p397" />

==Aperture diffraction==
A [[far-field]] pattern exists at distances that are large compared with ''s'' 2/λ, where ''s'' is a characteristic dimension of the source and λ is the [[wavelength]]. For example, if the source is a uniformly illuminated circle, then ''s'' is the radius of the circle.

The far-field diffraction pattern of a source may also be observed (except for scale) in the focal plane of a well-corrected lens. The far-field pattern of a diffracting [[screen]] illuminated by a [[wikt:point source|point source]] may be observed in the image plane of the source.

If a light source and an observation screen are effectively far enough from a diffraction aperture (for example a slit), then the [[wavefront]]s arriving at the aperture and the screen can be considered to be [[Collimated light|collimated]], or ''[[plane waves|plane]]''. [[Fresnel diffraction]], or ''near-field diffraction'' occurs when this is not the case and the curvature of the incident wavefronts is taken into account.

In far-field diffraction, if the observation screen is moved relative to the aperture, the diffraction pattern produced changes uniformly in size. This is not the case in near-field diffraction, where the diffraction pattern changes both in size and shape.

==Slit diffraction==
Fraunhofer diffraction through a slit can be achieved with two lenses and a screen. Using a point-like source for light and a [[collimating lens]] it is possible to make parallel light, which will then be passed through the slit. After the slit there is another lens that will focus the parallel light onto a screen for observation. The same setup with multiple slits can also be used, creating a different diffraction pattern.

Since this type of diffraction is mathematically simple, this experimental setup can be used to find the wavelength of the incident [[monochromatic]] light with high accuracy.

==Theory==
For an aperture with an amplitude transmittance <math>f(x)</math> on which plane waves are incident, the diffracted far-field amplitude as a function of the angle <math>\theta</math> with the propagation direction of the incident waves is
:<math>\psi(\theta) \propto \int_{-\infty}^{\infty} f(x) e^{i(k\theta)x} dx,</math>
where <math>k=2\pi/\lambda</math> is the [[wavenumber#In wave equations|circular wavenumber]] of the incident waves. The expression is the Fourier transform of the aperture function against the variable <math>k\theta</math>. This approximation is only valid for small values of <math>\theta</math>. Note that the aperture function acts on the ''amplitude'', not on the intensity (amplitude squared) of the waves. It can be complex-valued to indicate a phase shift.

==Examples==

===Diffraction from a slit===

The simplest example is Fraunhofer diffraction from a slit, i.e. <math>f(x) = 1</math> for <math>-a/2 < x < a/2</math> and <math>f(x)=0</math> elsewhere. In this case,
:<math>\psi(\theta) = \mathrm{sinc}(\pi a \theta/\lambda),</math>
The [[sinc|unnormalized sinc]] function peaks at <math>\theta=0</math> and has zeroes at <math>\theta=\pm n\lambda/a</math>, where <math>n=1, 2, \ldots</math>.

===Gaussian profile===

An aperture with a Gaussian profile <math>f(x) = \exp(-ax^2)</math> results in
:<math>\psi(\theta) = \exp\left(\frac{-k^2\theta^2}{4a}\right) .</math>
For example, if a laser beam has an intensity profile with a full width at half maximum (FWHM) <math>W</math>, then <math>a=2\ln 2/W^2</math>. At a wavelength <math>\lambda</math>, the amplitude profile is
:<math>\psi(\theta) = \exp\left(-\frac{\pi^2W^2}{2 \lambda^2\ln 2}\theta^2\right),</math>
i.e. an angular FWHM in the intensity of <math>2\lambda\ln 2/\pi W \approx 0.44\lambda/W</math>.

== See also ==
*[[Fresnel diffraction]]
*[[Fresnel number]]
*[[Huygens Principle]]

== External links ==

* [http://scienceworld.wolfram.com/physics/FraunhoferDiffraction.html Fraunhofer diffraction] on [[ScienceWorld]]
* [http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fraunhofcon.html Fraunhofer diffraction] on [[HyperPhysics]]

==Notes==
<references />
==References==
* {{cite book|author=Hecht, E.|title=Optics, 2nd edition|publisher=Addison Wesley|year=1987|id=ISBN 0-201-11611-1}}
*{{cite book|author=Jenkins, F., White, H.|title=Fundamentals of Optics, 4th edition|publisher=McGraw-Hill INC.|year=1976|id=ISBN 0-07-032330-5}}

[[Category:Diffraction]]

[[ja:フラウンホーファー回折]]

User talk:62.254.173.99

2007-01-18T23:19:01Z

JSpudeman: Snell's Law vandalism

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:Please refrain from removing content from Wikipedia, as you did to [[:Customer service]]. It is considered [[Wikipedia:Vandalism|vandalism]]. If you want to experiment, please use the [[Wikipedia:Sandbox|sandbox]]. Thank you.  [[User:68.39.174.238|68.39.174.238]] 14:19, 13 January 2006 (UTC)

Please stop. If you continue to blank pages, you will be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  ([[User:ESkog|ESkog]])([[User talk:ESkog|Talk]]) 14:27, 23 January 2006 (UTC)

Regarding the page [[:John Williams (composer)]], please stop. If you continue to vandalize pages, you will be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  [[User:Kcordina|Kcordina]] 09:41, 27 January 2006 (UTC)

[[Image:Stop_hand.png|left|30px]] This is your '''last warning'''. The next time you [[Wikipedia:Vandalism|vandalize]] a page, you ''will'' be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  [[User:Royboycrashfan|'''Roy'''al Blue]] [[User talk:Royboycrashfan|T]]/[[Special:Contributions/Royboycrashfan|C]] 15:08, 24 February 2006 (UTC)

Please refrain from adding nonsense to Wikipedia, as you did to [[:Concussion of the brain]]. It is considered [[Wikipedia:Vandalism|vandalism]]. If you would like to experiment, use the [[Wikipedia:Sandbox|sandbox]].  A link to the edit I have reverted can be found here: [http://en.wikipedia.org/w/index.php?title=Concussion_of_the_brain&diff=next&oldid=49692670 link]. If you believe this edit should not have been reverted, please contact me.  [[User:Jpkoester1|Jpkoester1]] 09:14, 28 April 2006 (UTC)

Please refrain from adding nonsense to Wikipedia, as you did to [[:Jean-Paul Gaultier]]. It is considered [[Wikipedia:Vandalism|vandalism]]. If you would like to experiment, use the [[Wikipedia:Sandbox|sandbox]].  [[User:GilliamJF|GilliamJF]] 11:22, 28 April 2006 (UTC)

Your recent edit to [[Shape memory alloy]] was reverted by an '''automated bot''' that attempts to recognize and repair [[Wikipedia:vandalism|vandalism]] to Wikipedia articles. If the bot reverted a legitimate edit, please accept our apologies – if you bring it to the attention of the bot's owner, we may be able to improve its behavior. '''[[User:Tawkerbot2/FAQ|Click here]]''' for '''frequently asked questions''' about the bot and this warning. // [[User:Tawkerbot2|Tawkerbot2]] 10:48, 4 May 2006 (UTC)

[[Image:Stop_hand.png|left|30px]] This is your '''last warning'''. The next time you vandalize a page, as you did to [[:Teflon]], you ''will'' be blocked from editing Wikipedia.  --[[User:Nlu|Nlu]] ([[User talk:Nlu|talk]]) 10:54, 9 May 2006 (UTC)

Please stop. If you continue to [[Wikipedia:Vandalism|vandalize]] pages, you will be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  --[[User:Ryan Delaney|Ryan Delaney]] [[User talk:Ryan Delaney|talk]] 10:37, 12 May 2006 (UTC)

Please refrain from adding nonsense to Wikipedia, as you did to [[:Russian Revolution]]. It is considered [[Wikipedia:Vandalism|vandalism]]. If you would like to experiment, use the [[Wikipedia:Sandbox|sandbox]].  [[User:Ravikiran r|Ravikiran]] 12:43, 15 May 2006 (UTC)

Please stop. If you continue to vandalize pages, as you did to [[:Russian Revolution]], you will be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  [[User:Ravikiran r|Ravikiran]] 12:47, 15 May 2006 (UTC)

==Your edit to [[Tasmania]]==
Your recent edit to [[Tasmania]] was reverted by an '''automated bot''' that attempts to recognize and repair [[Wikipedia:vandalism|vandalism]] to Wikipedia articles. If the bot reverted a legitimate edit, please accept my humble creator's apologies – if you bring it to the attention of the bot's owner, we may be able to improve its behavior. '''[[User:Tawkerbot2/FAQ|Click here]]''' for '''frequently asked questions''' about the bot and this warning. // [[User:Tawkerbot2|Tawkerbot2]] 08:33, 16 May 2006 (UTC)

[[Image:Stop_hand.svg|left|30px]] This is your '''last warning''' for editing [[River Ouse, Yorkshire]]. The next time you [[Wikipedia:Vandalism|vandalize]] a page, you ''will'' be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  // [[User:Tawkerbot2|Tawkerbot2]] 08:48, 16 May 2006 (UTC)

==Your edit to [[Pakistan]]==
Your recent edit to [[Pakistan]] was reverted by an '''automated bot''' that attempts to recognize and repair [[Wikipedia:vandalism|vandalism]] to Wikipedia articles. If the bot reverted a legitimate edit, please accept my humble creator's apologies – if you bring it to the attention of the bot's owner, we may be able to improve its behavior. '''[[User:Tawkerbot2/FAQ|Click here]]''' for '''frequently asked questions''' about the bot and this warning. // [[User:Tawkerbot2|Tawkerbot2]] 12:59, 17 May 2006 (UTC)

[[Image:Stop hand.svg|left|30px]] Welcome to Wikipedia. We invite everyone to contribute constructively to our encyclopedia. Take a look at the [[Wikipedia:Welcome, newcomers|welcome page]] if you would like to learn more about contributing. However, unconstructive edits are considered [[Wikipedia:Vandalism|vandalism]], and if you continue in this manner you may be '''[[Wikipedia:blocking policy|blocked]] from editing without further warning'''. Please stop, and consider improving rather than damaging the hard work of others. Thank you.  -- [[User:Wiki_alf|Alf]] [[User_talk:Wiki_alf|melmac]] 13:02, 17 May 2006 (UTC)

[[Image:Stop_hand.png|left|30px]] This is your '''last warning'''. The next time you vandalize a page, as you did to [[:Haggis]], you ''will'' be blocked from editing Wikipedia.  A link to the edit I have reverted can be found here: [http://en.wikipedia.org/w/index.php?title=Haggis&diff=next&oldid=58618255 link]. If you believe this edit should not have been reverted, please contact me.  [[User:Hoopydink/Esperanza|'''hoopydink''']][[User talk:Hoopydink|Conas tá tú?]] 08:16, 15 June 2006 (UTC)

[[Image:Stop_hand.png|left|30px]] This is your '''last warning'''. The next time you vandalize a page, as you did to [[:John Carroll (priest)]], you ''will'' be blocked from editing Wikipedia.  [[User:Netsnipe|Netsnipe]] 09:14, 20 June 2006 (UTC)

==Your edit to [[Mosque]]==
Your recent edit to [[:Mosque]] ([http://en.wikipedia.org/w/index.php?title=Mosque&diff=61366220&oldid=61238359 diff]) was reverted by an '''automated bot''' that attempts to recognize and repair [[Wikipedia:vandalism|vandalism]] to Wikipedia articles. If the bot reverted a legitimate edit, please accept my humble creator's apologies – if you bring it to the attention of the bot's owner, we may be able to improve its behavior. '''[[User:Tawkerbot2/FAQ|Click here]]''' for '''frequently asked questions''' about the bot and this warning. // [[User:Tawkerbot2|Tawkerbot2]] 12:54, 30 June 2006 (UTC)

==Regarding edits made during [[July 3]] [[2006]]==
[[Image:Stop hand.svg|left|30px]] Welcome to Wikipedia. We invite everyone to contribute constructively to our encyclopedia. Take a look at the [[Wikipedia:Welcome, newcomers|welcome page]] if you would like to learn more about contributing. However, unconstructive edits are considered [[Wikipedia:Vandalism|vandalism]], and if you continue in this manner you may be '''[[Wikipedia:blocking policy|blocked]] from editing without further warning'''. Please stop, and consider improving rather than damaging the hard work of others. Thank you.  ''If this is an [[IP address]], and it is shared by multiple users, ignore this warning if you did not make any [[Wikipedia:vandalism|unconstructive]] edits.'' [[User:Tangotango|Tangot]][[User:Tangotango/Esperanza|a]][[User Talk:Tangotango|ngo]] 13:13, 3 July 2006 (UTC)

:[[Image:Stop_hand.svg|left|30px]] This is your '''last warning'''. The next time you [[Wikipedia:Vandalism|vandalize]] a page, you ''will'' be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  [[User:Tangotango|Tangot]][[User:Tangotango/Esperanza|a]][[User Talk:Tangotango|ngo]] 13:14, 3 July 2006 (UTC)

[[Image:Stop_hand.png|left|30px]] This is your '''last warning'''. The next time you vandalize a page, as you did to [[:PlayStation Portable]], you ''will'' be blocked from editing Wikipedia.  A link to the edit I have reverted can be found here: [http://en.wikipedia.org/w/index.php?title=PlayStation_Portable&diff=next&oldid=61992005 link]. If you believe this edit should not have been reverted, please contact me.  [[User:Konstable|Konstable]] 09:14, 4 July 2006 (UTC)

:<div style="clear: both"></div>{{{1|[[Image:Octagon-warning.png|left|30px| ]] }}}'''You have been temporarily [[Wikipedia:Blocking policy|blocked]] from editing for vandalism of Wikipedia.''' Please note that page blanking, addition of random text or spam, deliberate misinformation, privacy violations, and repeated and blatant violation of [[Wikipedia:Neutral point of view|WP:NPOV]] are considered [[WP:VAND|vandalism]]. If you wish to make useful contributions, you may come back after the block expires.  [[User:Petros471|Petros471]] 09:44, 4 July 2006 (UTC)

==Your edit to [[:Gore-Tex]]==
Your recent edit to [[:Gore-Tex]] ([http://en.wikipedia.org/w/index.php?title=Gore-Tex&diff=74097086&oldid=70006829 diff]) was reverted by an '''automated bot''' that attempts to recognize and repair [[Wikipedia:vandalism|vandalism]] to Wikipedia articles. If the bot reverted a legitimate edit, please accept my humble creator's apologies – if you bring it to the attention of the bot's owner, we may be able to improve its behavior. '''[[User:AntiVandalBot/FAQ|Click here]]''' for '''frequently asked questions''' about the bot and this warning. // [[User:AntiVandalBot|AntiVandalBot]] 08:26, 6 September 2006 (UTC)

====Regarding edits made during [[September 6]] [[2006]] ([[UTC]]) to [[Kevlar]]====
Please do not add nonsense to Wikipedia; it is considered [[Wikipedia:Vandalism|vandalism]]. If you would like to experiment, use the [[Wikipedia:Sandbox|sandbox]]. Thank you.  ''If this is an [[IP address]], and it is shared by multiple users, ignore this warning if you did not make any [[Wikipedia:vandalism|unconstructive]] edits.'' [[User:MER-C|MER-C]] 09:44, 6 September 2006 (UTC)

==Your edit to [[:Autostereogram]]==
Your recent edit to [[:Autostereogram]] ([http://en.wikipedia.org/w/index.php?title=Autostereogram&diff=74494595&oldid=74494501 diff]) was reverted by an '''automated bot''' that attempts to recognize and repair [[Wikipedia:vandalism|vandalism]] to Wikipedia articles. If the bot reverted a legitimate edit, please accept my humble creator's apologies – if you bring it to the attention of the bot's owner, we may be able to improve its behavior. '''[[User:AntiVandalBot/FAQ|Click here]]''' for '''frequently asked questions''' about the bot and this warning. // [[User:AntiVandalBot|AntiVandalBot]] 09:16, 8 September 2006 (UTC)
:Please refrain from adding nonsense to Wikipedia, as you did to [[:Autostereogram]]. It is considered [[Wikipedia:Vandalism|vandalism]]. If you would like to experiment, use the [[Wikipedia:Sandbox|sandbox]].  [[User:Soosed|Soosed]] 09:17, 8 September 2006 (UTC)

====Regarding edits made during [[September 15]] [[2006]] ([[UTC]]) to [[Solar power satellite]]====
Thank you for experimenting with Wikipedia. Your test worked, and it has been [[Help:Reverting|reverted]] or removed. Please use [[Wikipedia:Sandbox|the sandbox]] for any other tests you want to do. Take a look at the [[Wikipedia:Welcome, newcomers|welcome page]] if you would like to learn more about contributing to our encyclopedia. ''If this is an [[IP address]], and it is shared by multiple users, ignore this warning if you did not make any [[Wikipedia:vandalism|unconstructive]] edits.'' [[User:MER-C|MER-C]] 09:17, 15 September 2006 (UTC)

==Your edit to [[:Wikipedia:Ownership of articles]]==
Your recent edit to [[:Wikipedia:Ownership of articles]] ([http://en.wikipedia.org/w/index.php?title=Wikipedia%3AOwnership_of_articles&diff=76385217&oldid=76316131 diff]) was reverted by an '''automated bot''' that attempts to recognize and repair [[Wikipedia:vandalism|vandalism]] to Wikipedia articles. If the bot reverted a legitimate edit, please accept my humble creator's apologies – if you bring it to the attention of the bot's owner, we may be able to improve its behavior. '''[[User:AntiVandalBot/FAQ|Click here]]''' for '''frequently asked questions''' about the bot and this warning. // [[User:AntiVandalBot|AntiVandalBot]] 10:04, 18 September 2006 (UTC)

== Please stop ==

Please stop vandalizing the BioFuel-article. Use the [[Wikipedia:sandbox]] for experiments. Thank you. --[[User:Warfvinge|Warfvinge]] 10:42, 19 September 2006 (UTC)

Please stop. If you continue to [[Wikipedia:Vandalism|vandalize]] pages, you will be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  -- [[User:Warfvinge|Warfvinge]] 10:44, 19 September 2006 (UTC)

== Last Warning ==

[[Image:Stop_hand.svg|left|30px]] This is your '''last warning'''. The next time you vandalize a page, as you did to [[:Biofuel]], you ''will'' be blocked from editing Wikipedia.  —The preceding [[Wikipedia:Sign your posts on talk pages|unsigned]] comment was added by [[User:Warfvinge|Warfvinge]] ([[User talk:Warfvinge|talk]] • [[Special:Contributions/Warfvinge|contribs]]) 10:46, September 19, 2006 (UTC{{{3|}}})

<div style="padding:5px; border: 1px solid #ccc; background:#FFF; clear:both" class="user-block"> [[Image:Modern clock chris kemps 01 with Octagon-warning.svg|left|40px]] You have been [[Wikipedia:Blocking policy| blocked]] from editing for a period of 31 hours for [[Wikipedia:Vandalism|vandalizing]] Wikipedia. If you wish to make useful contributions, you are welcome to come back after the block expires. {{{2|[[User:Netsnipe|'''  Netsnipe ''']][[User talk:Netsnipe| ► ]] 11:19, 19 September 2006 (UTC)}}}  </div>

{{unblock-auto reviewed|62.254.173.99|repeated vandalism for several days - AO}}

==Your edits to [[Photogram]]==
[[Image:Stop_hand.svg|left|30px]] This is your '''last warning'''. The next time you [[Wikipedia:Vandalism|vandalize]] a page, {{#if:{{{1|}}}|as you did to [[:{{{1}}}]],}} you ''will'' be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia. Th[[User:Theone00/Esperanza|e]] One00 10:23, 30 October 2006 (UTC)

<div class="user-block" style="clear:both;">[[Image:Octagon-warning.svg|30px|left]] '''You have been [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia for repeated [[Wikipedia:Vandalism|vandalism]].''' If or when the block expires, feel free to come back, but please make useful contributions instead, and refrain from vandalising or this account will face longer blocks, and action could be taken against the individual who uses it.  --[[User:Samuel Blanning|Sam Blanning]][[User talk:Samuel Blanning|(talk)]] 11:46, 30 October 2006 (UTC)

== January 2007 ==

Hello, and [[Wikipedia:Welcome, newcomers|welcome to Wikipedia]]! We welcome and appreciate your contributions, such as those in [[{{{1}}}]], but we regretfully cannot accept [[Wikipedia:No original research|original research]]. Please be prepared to [[Wikipedia:Cite your sources|cite a reliable source]] for all of your information. Thanks for your efforts, and happy editing!  — [[User talk:Sir Nicholas de Mimsy-Porpington|'''Nearly Headless Nick''']] 09:46, 9 January 2007 (UTC)

==Regarding edits made during January 9 2007==
Thank you for experimenting with {{#if:{{{1|}}}|the page [[:{{{1}}}]] on}} Wikipedia. Your test worked, and it has been [[Help:Reverting|reverted]] or removed. Please use [[Wikipedia:Sandbox|the sandbox]] for any other tests you may want to do. Take a look at the [[Wikipedia:Introduction|welcome page]] to learn more about contributing to our encyclopedia. ''If this is an [[IP address]], and it is shared by multiple users, ignore this warning if you did not make any [[Wikipedia:vandalism|unconstructive]] edits.'' [[User:Tangotango|Tangotango]] ([[User talk:Tangotango|talk]]) 15:00, 9 January 2007 (UTC)

==Regarding edits made during January 9 2007==
Please stop. If you continue to [[Wikipedia:Vandalism|vandalize]] pages, {{#if:{{{1|}}}|as you did to [[:{{{1}}}]],}} you will be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  ''If this is an [[IP address]], and it is shared by multiple users, ignore this warning if you did not make any [[Wikipedia:vandalism|unconstructive]] edits.'' [[User:Tangotango|Tangotango]] ([[User talk:Tangotango|talk]]) 15:14, 9 January 2007 (UTC)

Your recent edit to [[:Point of sale]] ([http://en.wikipedia.org/w/index.php?title=Point_of_sale&diff=100839830&oldid=100357310 diff]) was reverted by an '''automated bot''' that attempts to recognize and repair [[Wikipedia:vandalism|vandalism]] to Wikipedia articles. If the bot reverted a legitimate edit, please accept my humble creator's apologies – if you bring it to the attention of the bot's owner, we may be able to improve its behavior. '''[[User:AntiVandalBot/FAQ|Click here]]''' for '''frequently asked questions''' about the bot and this warning.  // [[User:AntiVandalBot|AntiVandalBot]] 09:25, 15 January 2007 (UTC)

====Regarding edits made during [[January 15]] [[2007]] ([[UTC]]) to [[Point of sale]]====
Please stop. If you continue to blank pages, {{{{{subst|}}}#if:{{{1|}}}|as you did to [[:{{{1}}}]],}} you will be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  ''If this is an [[IP address]], and it is shared by multiple users, ignore this warning if you did not make any [[Wikipedia:vandalism|unconstructive]] edits.'' —[[User:Ryulong|Ryūlóng]] ([[User talk:Ryulong|竜龍]]) 09:26, 15 January 2007 (UTC)

====Regarding edits made during [[January 15]] [[2007]] ([[UTC]])====
[[Image:Stop_hand.svg|left|30px]] This is your '''last warning'''. The next time you [[Wikipedia:Vandalism|vandalize]] a page, {{#if:{{{1|}}}|as you did to [[:{{{1}}}]],}} you will be [[Wikipedia:Blocking policy|blocked]] from editing Wikipedia.  ''If this is an [[IP address]], and it is shared by multiple users, ignore this warning if you did not make any [[Wikipedia:vandalism|unconstructive]] edits.'' [[User:FrancoGG|FrancoGG]] ''( [[User talk:FrancoGG|talk]] )'' 14:47, 15 January 2007 (UTC)

==== Regarding edits to [[Snell's Law]] ====
[[Image:Stop_hand.svg|left|30px]] Please refrain from removing information from articles that has undergone review. Removal of information is classed as vandalism, and can result in further banning from the wikipedia. [[User:JSpudeman|James S]] 23:19, 18 January 2007 (UTC)

User talk:Dicklyon

2007-01-18T10:14:22Z

JSpudeman:

== DLP ==

In [[DLP#Three-chip_projectors]], you deleted the following text:

<blockquote>Single-chip DLP systems are capable of displaying 16.7 million (24-bit) colors, whereas three-chip DLP systems can display up to 35 trillion (45-bit) colors.</blockquote>

Your edit comment characterized the text that you removed as "silly numerology", once again displaying the gratuitous rudeness that is a frequent feature of your WP participation and is unnecessarily disruptive of collaborative editing.

The explanation that you added is, of course, a worthwhile contribution to the article. However, unless the text that you deleted is inaccurate, it seems to me that the specifics belong in the article in addition to your explanation. Are the deleted data inaccurate? If not, they should be restored. If the data are accurate, I would suggest restoring them after your explanation substantially as follows:

<blockquote>Hence, three-chip DLP systems can display up to 35 trillion (45-bit) colors, whereas single-chip DLP systems are limited to 16.7 million (24-bit) colors.</blockquote>

Further, you really should modify your editing behavior rather than having to apologize so often for it.

[[User:Finell|Finell]] [[User_talk:Finell|(Talk)]] 14:30, 26 October 2006 (UTC)

:I felt that "silly numerology" would be the best way to characterize what was there. I can't help it that you don't like my style, so, per your suggestion, no apology. [[User:Dicklyon|Dicklyon]] 15:03, 26 October 2006 (UTC)

::Please answer: Are the numbers that you removed correct or incorrect? They weren't mine, by the way, so no apology would be due me in any event. Actually, I do like the "style" of the writing you contribute to WP. It is usually a clear and concise expression of worthwhile content. The explanation that you added to [[DLP#Three-chip_projectors]] is a fine example of your very useful contributions. However, I am far from the only Wikipedian who is bothered by your disruptive manner and rude words; others have expressed the same to you. Rudeness is not a "style"; it is anti-social behavior in which you persist. For some time I tried to correct your behavior gently and diplomatically. As that approach failed to improve your behavior, I have become increasingly blunt—a "style" that you ought to understand. [[User:Finell|Finell]] [[User_talk:Finell|(Talk)]] 20:12, 26 October 2006 (UTC)

:::Yes, I get your blunt style. I'm still a bit unsure, though, why a comment about the removed material being "silly numerology" sets you off. It's a fair characterization of the material, and connotes my attitude toward it fairly, and is hence an informative explanation for my edit.

::::Condemning the conscientious (even if sometimes misguided or mistaken) contributions of other editors, who donate their time to WP, as "silly" or "twaddle" is rude and insulting. That is what "sets [me] off", and sets off other editors. You may think that you are merely criticizing text, but in fact you are insulting the human being who wrote it. Frankly, I don't understand why this is not obvious to you, intelligent as you are. When another editor (an admin) called you out for a similarly rude edit summary, you asked if there was some official governing etiquette. I quoted to you from '''[[Help:Edit_summary#Use_of_edit_summaries_in_disputes|WP:ES—Use of edit summaries in disputes]]''', which says, in part, "Avoid using edit summaries ... to express opinions of the other users involved." ''That'' is policy, and it trumps your urge to express your self-perceived superiority over others. Look at the number of criticisms of your behavior, on your own talk page and on the talk pages of articles that you edit. Most active Wikipedians do not draw such criticisms with anywhere near the frequency that you do, and for every criticism that you see, figure that there are 10 more who are equally offended but who lack the courage to confront you. What do you gain by this behavior? More importantly, what does WP gain, and what does it lose, by it? If nothing else, aren't the arguments that you inspire a waste of your time and the time of others? As you see, I have not given up hope of reforming you. I have repeatedly said that you have very worthwhile contributions to make to WP, and I hope you will continue to make them. However, your repeated rudeness, which your own numerous apologies admit, diminishes your usefulness and the willingness of others to accept your edits. [[User:Finell|Finell]] [[User_talk:Finell|(Talk)]] 08:26, 27 October 2006 (UTC)
:::::Finell, I hear your point, but I don't agree that I've operated outside the suggested policy here. "Silly numerology" was an objective comment on the text, not a remark about the person who wrote it. It is a concise way to let that person know that what he wrote may make sense numerologically, but not otherwise. I didn't think I needed to do some politicing on the talk page to document the reason for a simple edit. And there was no argument, either prior to or inspired by my comment, except from you. Now go home. And as for that other admin, one has to wonder who allowed him to become that, increasing his abusive use of power. It you want to see how one recomes involved in raging arguments, even while remaining polite on surface, study his history. Now go away and stop bothering me. [[User:Dicklyon|Dicklyon]] 15:02, 27 October 2006 (UTC)
::::::Dick: I will continue my efforts to socialize your WP behavior when I see behavior that warrants it, but ''not'' otherwise. I am as persistent as you are stubborn. [[User:Finell|Finell]] [[User_talk:Finell|(Talk)]] 16:57, 27 October 2006 (UTC)
:::::::OK, I look forward to your input. Not. [[User:Dicklyon|Dicklyon]] 17:00, 27 October 2006 (UTC)
:::::::Hey, Finell, did you notice the high praise and agreement I got from my nemesis? He said "OK"; the nicest word I've got out of him. Even nicer, he didn't revert my changes now that I've proven that truth and verifiability are not in conflict. [[User:Dicklyon|Dicklyon]] 05:21, 31 October 2006 (UTC)
:::As to whether the numbers are "correct", what do you mean by that? If you mean can one sensibly expect to get 2^(3*15) different colors out of a projector, no, that's just silly numerology. [[User:Dicklyon|Dicklyon]] 23:10, 26 October 2006 (UTC)

Thanks for adding the information on the CBS Color wheel standard. I thought the information was interesting, but it needed a link, so I reverted someone's earlier edit. What you put back helped out a lot! Thank you! --[[User:Mdwyer|Mdwyer]] 17:58, 27 November 2006 (UTC)

==[[Mousepad]] problems==

Hey. I've been keeping an eye on [[Mousepad]] lately, 'cause it seems to be a target for a lot of vandalism, or at least harmful edits. It seems like the same person is doing them, too, overemphasizing stuff and introducing grammatical errors. I noticed you've been working on the article -- or at least getting rid of the semi-vandalism. Would you mind keeping a closer eye on it? It's not that popular an article, and I'm having some trouble dealing with the bad edits, so I wondered if you're interested in helping out/cleaning up. [[User:Switchercat|Switchercat]] [[User_talk:Switchercat|talk]][[Special:Contributions/Switchercat|cont]] 01:47, 1 November 2006 (UTC)

Thanks for fixing the "silicon/e" bits in my reversion, by the way, as I seem to have been a little too brutal with the changes. Good to know that that anon user is correcting some factual errors, at least. [[User:Switchercat|Switchercat]] [[User_talk:Switchercat|talk]][[Special:Contributions/Switchercat|cont]] 01:49, 1 November 2006 (UTC)

:I was thinking of recommending it for deletion. It's obviously written by the inventor himself, trying to stake his claim to fame. It's perhaps a partially fair claim, backed up by the Xerox disclosure journal, but the amount of verbage about him is ridiculous, as is not citing Engelbart who showed a mousepad 10 years earlier. It needs work if it stays. Who has time to take on such a trivial thing, though? I got onto it via some bad stuff he put in the mouse article, which I watch. [[User:Dicklyon|Dicklyon]] 02:48, 1 November 2006 (UTC)
::My dad worked at Xerox around that time, actually, and he's contesting some of the stuff. Says they first used vinyl board cover, not silicone. (And he just looks at what I'm writing and goes, "Dick Lyon! Richard Lyon? Did he work for Xerox too? He did optical mouse." I don't know if you're that guy, but that's kind of interesting.) Mousepads seem notable enough that a vote for deletion wouldn't get rid of it. It ''is'' trivial, yeah; I suspect I'll revert the vandalism and leave it at that for now. Thanks for the input on the disclosure journal, though; I might look into that if I feel like contributing more. [[User:Switchercat|Switchercat]] [[User_talk:Switchercat|talk]][[Special:Contributions/Switchercat|cont]] 03:11, 1 November 2006 (UTC)
:::Yep, that's me. All older now, and wasting my time on wikipedia. Who's your dad? He can mail my handle at acm.org. [[User:Dicklyon|Dicklyon]] 04:26, 1 November 2006 (UTC)

== Gutenberg ==

Very helpful recent edits.including a better wording for my awkward phrase. [[User:DGG|DGG]] 04:27, 14 November 2006 (UTC)
:please check the Village Pump (policy) for an attempt to reopen some related issues.[[User:DGG|DGG]] 05:07, 18 November 2006 (UTC)

== Re: Stop capitalizing ==

Sorry About That - I didn't read that. I have a thing for capitalized titles.
[[User:Christopher Kraus|Christopher Kraus]] 01:22, 16 November 2006 (UTC)
:No problem. I fixed one already, and assume you'll take care of it. Welcome to WP. [[User:Dicklyon|Dicklyon]] 01:25, 16 November 2006 (UTC)

== Supernumeray rainbow image ==

Hi Dicklyon, 
I woud disagree with the replacement as the image I uploaded is of higher res and better quality --[[User:Fir0002|Fir0002]] 05:12, 21 November 2006 (UTC)

:But the green and purple stripes are not as easy to see as in the one you replaced. [[User:Dicklyon|Dicklyon]] 06:18, 21 November 2006 (UTC)

== Gutenberg ==

Thxs for making my talk page stuff clearer. M has moved on to woodcut now, so maybe things will be quieter for you!
[[User:Johnbod|Johnbod]] 20:21, 26 November 2006 (UTC)

== Re:Logarithms.png ==

Looks great! Thanks for letting me know. [[User:Enochlau|enochlau]] ([[User talk:Enochlau|talk]]) 08:56, 27 November 2006 (UTC)

== Old VICAR manuals ==

Sorry but I can't help you with that, I just stumbled on to Billingsley's link with VICAR by coincidence so I added it to the wiki.--[[User:Rxke|Rxke]] 11:02, 29 November 2006 (UTC)

==''West wikipedia'' weirdness==

I demoted all this related stuff from sections to subsections. [[User:Dicklyon|Dicklyon]] 01:26, 18 December 2006 (UTC)

===STOP THE HARASSMENT===
Do NOT delete my external links. The external links that I provide have 100% to do with the article I leave them on. You need to leave my links online as they meet the wikipedia external links policy. —The preceding [[Wikipedia:Sign your posts on talk pages|unsigned]] comment was added by [[User:West wikipedia|West wikipedia]] ([[User talk:West wikipedia|talk]] • [[Special:Contributions/West wikipedia|contribs]]) 05:41, 9 December 2006 (UTC).

:It is customary to answer on the page where the conversation was started. Read the reasons there (on your talk page), instead of deleting them. It is not harassment, just trying to help wikipedia stick to policies. [[User:Dicklyon|Dicklyon]] 05:43, 9 December 2006 (UTC)

===STOP===
I also left this on my user page. You are a spammer and you need to knock it off! Quit deleting relevant external links —The preceding [[Wikipedia:Sign your posts on talk pages|unsigned]] comment was added by [[User:West wikipedia|West wikipedia]] ([[User talk:West wikipedia|talk]] • [[Special:Contributions/West wikipedia|contribs]]) 05:48, 9 December 2006 (UTC).

:I'm amused by your interpretation. [[User:Dicklyon|Dicklyon]] 05:50, 9 December 2006 (UTC)

I also left this on my discussion page - It meets the criteria... You need to stop doing this. If you think this is a violation then why dont you wait and see if any of the other millions of users do

:Not a violation, just not in accord with editorial policies. I'm sure someone else will revert you after I go to bed. [[User:Dicklyon|Dicklyon]] 06:00, 9 December 2006 (UTC)

=== Re: your recent revert to [[Luck]] ===

Hello! Just wanted to ask you about your curious edit [http://en.wikipedia.org/w/index.php?title=Luck&curid=192727&diff=93094615&oldid=92819227 here]. I'm thinking, based on my review of your interaction with [[User:West wikipedia|West wikipedia]], that it may have been an error. I've been doing what I see you do; removing superfluous external links, but your reversion there actually restored them. Heh. Anyway. Just curious. Thanks! -- '''[[User:Weirdoactor|weirdoactor]] [[User talk:Weirdoactor|t]]|[[Special:Contributions/Weirdoactor|c]]''' -- 06:21, 9 December 2006 (UTC)

:Yeah, I goofed on that one by not reading your diff; already reverted myself and apologized. Thanks. [[User:Dicklyon|Dicklyon]] 06:23, 9 December 2006 (UTC)

::No worries! Like I said, it looked like an error, and not malicious. Have a good one! -- '''[[User:Weirdoactor|weirdoactor]] [[User talk:Weirdoactor|t]]|[[Special:Contributions/Weirdoactor|c]]''' -- 06:26, 9 December 2006 (UTC)

=== West wikipedia ===

Is there a reason you reverted and deleted my comment on his talk page? I'm just wondering. - [[User:EronMain|Eron]] [[User Talk:EronMain|Talk]] 17:04, 9 December 2006 (UTC)

:Did I do that wrong? My intention was to restore your comment that he deleted. [[User:Dicklyon|Dicklyon]] 17:17, 9 December 2006 (UTC)

::I'm looking at [http://en.wikipedia.org/w/index.php?title=User_talk%3AWest_wikipedia&diff=93171449&oldid=93168204 this diff]. I think he deleted a comment before mine, and then you reverted to restore that deletion. He hasn't actually edited the page since I commented. No worries, it was an honest mistake. I just wanted to make sure there wasn't a perceived problem with my comment. Thanks. - [[User:EronMain|Eron]] [[User Talk:EronMain|Talk]] 17:22, 9 December 2006 (UTC)

=== Absolute Jerk ===
This is extremely innapporiate and childesh of you to put this kind of material on wikiepdia. "Speaking of external links, this guy User:West wikipedia is spamming lots of pages with his links to his earlyhistory.googlepage.com pages, which are trivialized histories with lots of error, not anything useful. If he puts one back here, someone else deal with him for a while, as I'm getting tired of it. Dicklyon 06:08, 9 December 2006 (UTC)" Because of you and your stupidish child like behavior I am no longer planning on ever using wikipedia. You need to grow up. How old are you? Maybe 11 or 12. Have a good day
West wikipedia {{unsigned|West wikipedia}}

:OK, I will. [[User:Dicklyon|Dicklyon]] 20:20, 9 December 2006 (UTC)

==Climate change==

Thank you for cleaning up my text on 'Climate change' The only reason that I intruded into the
article was to correct one statement about all the energy in the earths climate system coming from the sun. Energy and heat are not the same, the energy needed to keep the atmosphere in place on the surface of the earth comes from gravity, while the energy used to move warm air from the equator to the poles is the spinning of the earth. The source of the heat comes from the sun and I would imagine its close to 99.9 percent. While friction might contribute some heat and geothermal some, its very small. Note if you go into caves or mines most any were in the world the tempeture. is lower than the yearly average of the surface for that location ( the same for the bottom of the oceans) - so geothermal does not contribute much if any surface warming. Thank you for your time. [[User:Hardyplants|Hardyplants]] 11:27, 14 December 2006 (UTC)

:You're welcome, but I think you're very confused about what energy is. I just fixed the grammar. [[User:Dicklyon|Dicklyon]] 16:44, 14 December 2006 (UTC)

== "Dither" dictionary images ==

Hello! Thanks very much for uploading the images of old dictionary definitions; I found them extremely interesting. However, I did remove them from the article [[Dither]], because they really aren't relevant to image dithering, no matter how interesting they are on their own.

Have you looked into [[Wiktionary]]'s policy on images? I've never seen an image on Wiktionary, but if they ''are'' image-friendly, that would be the perfect place for those images. [[Dither]] already links to [[wikt:dither]], so they'd be almost as accessible from there. --[[User:Quuxplusone|Quuxplusone]] 19:15, 14 December 2006 (UTC)

:I thought the images supported the "origin of the word" section pretty well, by showing that the meaning was long established and just got adapted to this technical use. It's often hard to find good PD images for articles, which look so drab as just text. I might put them back... why don't you bring up the question of relevant on the talk page and see how others feel? [[User:Dicklyon|Dicklyon]] 19:23, 14 December 2006 (UTC)

==Ludvikus's octothorp tirades==

I demoted all these sections to subsections. [[User:Dicklyon|Dicklyon]] 01:23, 18 December 2006 (UTC)

=== [[Octothorp]] ===
I object your suppression of the above term without discussion on the discussion page.
:You could, if you wish, comment on its use,or lack thereof, but you cannot ignore the fact that it is the name for the "number sign" according to [[Merriam-Webster's]]!!!
::[[Yours truly,]]--[[User:Ludvikus|Ludvikus]] 04:47, 17 December 2006 (UTC)
:Don't worry, it is not being ignored. In fact it was I who added most of the content of the octocthorp section, including the mention of the Merriam-Wester Book of Word Histories 1991 article. You should read that one. Maybe I'll add a quote from it. I also am in contact with two of the guys that have written up their claims for having originated the term when at AT&T: Doug Kerr and Lauren Asplund; I need to write up a bit about the latter now that he has sent me his evidence, which doesn't actually say much. [[User:Dicklyon|Dicklyon]] 06:18, 17 December 2006 (UTC)
:By the way, the first google hit for octothorpe, at World Wide Words, say "This word is beginning to appear in a few dictionaries, but still seems mostly to be a jargon term of the North American telephone business. It has reached semi-official status by being mentioned in international standards documents but that’s no guarantee of a wide circulation any time soon." This is about how it should be represented in the article, not as an accepted or widely used term. [[User:Dicklyon|Dicklyon]] 06:22, 17 December 2006 (UTC)

=== Octothorpe ===
Google hits: 74,200 [http://www.google.com/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=Octothorpe&spell=1]
:[[Yours truly,]]--[[User:Ludvikus|Ludvikus]] 04:58, 17 December 2006 (UTC)
::And number-sign and pound-sign each have over a half million. So what? [[User:Dicklyon|Dicklyon]] 06:12, 17 December 2006 (UTC)

===Octothorp 2===
''It seems people are unaware that this term had entered the language in [[1971]]:'' '''octothorp \ak-te-thorp, -to-\ noun [octo- + thorp, of unknown origin; fr. the eight points on its circumference] (1971)'''
:'''the symbol #'''
:'''C) 1996 Zane Publishing, Inc. and Merriam-Webster, Incorporated'''
::[[Yours truly,]]--[[User:Ludvikus|Ludvikus]] 04:57, 17 December 2006 (UTC)
:Why do you think we are unaware? Read what the article says. Octothorp remains an obscure and unofficial name for the number sign, and we should not be elevating it the way you have. I have reverted your changes. Anyone object? [[User:Dicklyon|Dicklyon]] 15:46, 12 December 2006 (UTC)

::Google hits for [[Octothorp]]: 24,800 [http://www.google.com/search?hl=en&q=Octothorp&btnG=Google+Search]
:[[Yours truly,]]--[[User:Ludvikus|Ludvikus]] 04:57, 17 December 2006 (UTC)

=== [[Unicode]] vs. [[Typewriter]] & [[Telephone]] ===

*[[Unicode]] is a relatively recent technical usage.

*The [[Typewriter]] has been arround since the 19th century - and though I have not, every typewriter I have used or come accross had this [[octothorp]] or [[number sign]] on its ASCII type set.

*Similarly, since the 12-botton phone key-pad has been arround (I don't recall the situation regarding the rotary phone), the symbol, "'''#'''", has been arround. So it is not what the [[Unicode]] community legislates that is to be prioritized. Rather, it is the common users of the typewriter and telephone who give us the meaning of this sign or symbol. --[[User:Ludvikus|Ludvikus]] 20:15, 17 December 2006 (UTC)

::The term ''octothorp'' comes from the telephone guys after they developed the 12-key pad, as extensively documented in the article and its referenced and linked sources. Do you have anything to add? [[User:Dicklyon|Dicklyon]] 01:23, 18 December 2006 (UTC)

=== [[ASCII]] ===
[[Image:Ascii full.png|right]]

In other words, I'm talking about the 32 [[ASCII]] charaters!
:And I'm asking you, '''what is the 3rd character called?'''
:Are you going to omit--AT THE TOP PARAGRAPH--the uncommon name [[octothorp]]? Why? Because of [[Unicode]] conventions? I did not find that convention in Merriam-Webster when I looked up the term!
::What's the third sign/symbol called, besides "number sign"? Here's a picture for you:

:::[[Yours truly,]] [[User:Ludvikus|Ludvikus]] 20:39, 17 December 2006 (UTC)

::::Everything I can find about ASCII calls it "number sign"; see for example [http://www.columbia.edu/kermit/ascii.html this table] which might be from the standard (not sure). Its other names are all discussed at length in the [[number sign]] article. Please add to it if anything was missed. Octothorp was not missed. [[User:Dicklyon|Dicklyon]] 01:23, 18 December 2006 (UTC)

=== [[Number sign]] & 1994-1996 [[Merriam-Webster's]] ===
*By the way, there's no entry for "[[number sign]]" in said MW!!!
:So much the worse for "number sign," but better ''for my beloved'' "octothorp"!!! [[User:Ludvikus|Ludvikus]] 20:44, 17 December 2006 (UTC)
[[Yours truly,]]--[[User:Ludvikus|Ludvikus]] 20:49, 17 December 2006 (UTC)

:Your emotional attachment to an obscure name for a character that has a standard name is hardly encyclopedic. Get over it. [[User:Dicklyon|Dicklyon]] 01:23, 18 December 2006 (UTC)

==Your edit to [[:Johannes Gutenberg]]==
Your recent edit to [[:Johannes Gutenberg]] ([http://en.wikipedia.org/w/index.php?title=Johannes_Gutenberg&diff=95015526&oldid=95010430 diff]) was reverted by an '''automated bot''' that attempts to recognize and repair [[Wikipedia:vandalism|vandalism]] to Wikipedia articles. If the bot reverted a legitimate edit, please accept my humble creator's apologies – if you bring it to the attention of the bot's owner, we may be able to improve its behavior. '''[[User:AntiVandalBot/FAQ|Click here]]''' for '''frequently asked questions''' about the bot and this warning. // [[User:AntiVandalBot|AntiVandalBot]] 14:05, 18 December 2006 (UTC)

== [[Philosophy]]==
Dear [[User:Dicklyon]],
*We first have encountered one another over the article on the [[Number sign]].
**You might perhaps recall that I was rather partial to the more poetic, [[Orobouros]]?
***I - civily I might add - differred to your, probably much more studied position.
*Subsequently, we met over [[Book design]] vs. the much newer article, [[Book elements]]. That, I think you'll agree, is currently in a state of flux.
*Be that as it may, I write to you in the hope that I might get your assistance in an area of my special expertise, which [[Philosophy]].
**I've encountered a particularly subborn user, and I thought that, possibly, you might be of assistance in resolving the conflict!
***Will you please visit the article and see if you could contribute a ressolution?
****I do not wish to engage in the game of--what I call--ping-pong REVERSIONS!!!
:[[Yours truly,]] [[User:Ludvikus|Ludvikus]] 18:43, 28 December 2006 (UTC)
Ludvikus, perhaps I should be flattered that you think I can be more stubborn than your current nemesis. However, I'm no expert in philosophy, and after quick look I don't see how to contribute to the argument that seems to be primarily over the scope of the article. You might consider proposal separate articles on eastern and western philosophies, and make the main article simply a dispath page for those. Take it to the talk page and see if you can get some consensus. When it's just two editors arguing, it's unlikely to resolve. [[User:Dicklyon|Dicklyon]] 21:37, 28 December 2006 (UTC)

== Snell's Law ==

Sorry, i should have explained my comment further. It's strange, but the amount of books which include snell's law usually just expand onto wavelength and phase velocity when it's nothing to do with snell's law, implicitly. Well, good work on the change, anyway - i bought [[User:JCraw]] an optics book this x-mas for him to devour.

Still, snell's law in it's normal sense is expressed as <math>_1n_2 = \frac{\sin \theta_1}{\sin \theta_2}</math>, isn't it? In that case, the wavelengths and other things, providing they are expressed in the same units would result in a the refractive index anyway, wouldn't they? After all, the angle of refraction is expressed through the use of the refractive indecies isn't it? Well, it's been a while since i did physics.. it was 10 years ago when i did it in university :-/ [[User:JSpudeman|James S]] 20:15, 28 December 2006 (UTC)

:Your equation is a bit malformed, but I suppose you mean a form that is solved for an index of refraction. It's true that you an also express that index in terms of wavelengths or velocities. But that's not Snell's law, which is the law about the angles. [[User:Dicklyon|Dicklyon]] 21:39, 28 December 2006 (UTC)

::That equation seems fine.. i've seen it wrote that way many times, just as shorthand for the second refractive index. [[Image:SConfident.gif|15px]] [[User:JCraw|J O R D A N]] <nowiki>[</nowiki>[[User talk:JCraw|talk]] <nowiki>]</nowiki> 12:41, 2 January 2007 (UTC)

::The equation starts with a subscript 1 and has no n1 in it; if that's intentional, please explain. [[User:Dicklyon|Dicklyon]] 18:46, 2 January 2007 (UTC)

== Electronic circuit ==

Thanks for your help on the circuits pages. I did not realize it was a violation of protocol to move text from one page to another. Next time, I'll check the policies first. In the meantime, can you delete [[Electral circuit]]? I think there are some redirects on the talk pages which put everything on the talk page for Electral circuit, so those should be changed first.

:You're welcome. Moving material is not a violation, but moving whole pages is. You may have been over the border. Use the move link next time. I'll add a "prod" to the electral page. [[User:Dicklyon|Dicklyon]] 08:10, 2 January 2007 (UTC)

By the way, can you deal with the apparent contradiction between [[Active device]] and [[Active component]]? It seems there are two different usages for these terms:

1. transistors, vacuum tubes, etc.
2. power sources

It would be convenient if there were a 1:1 relationship between scientific concepts and the terms that refer to them, but we don't live in that world. I think an information source such as Wikipedia should clarify ambiguities by defining all usages, not arbitrarily selecting one and pretending that there is no other usage. Since you are an engineer, you are probably much more familiar with the literature than I am. I'd rather ask someone like you to do it than leave a <nowiki>{{Contradict-other|[[Article]]}}</nowiki>

--[[User:Cbdorsett|Cbdorsett]] 07:33, 2 January 2007 (UTC)

:Yeah, it's not so clean. "Active" is used for the things that produce electrical energy as well as for things that can be used to get some gain or oscillation in a circuit. And what about a diode? Is that active? Depends on your source; see [http://books.google.com/books?as_q=diode&num=10&btnG=Google+Search&as_epq=active-devices&as_oq=&as_eq=&as_libcat=0&as_brr=0&as_vt=&as_auth=&as_pub=&as_drrb=c&as_miny=&as_maxy=&as_isbn= GBS]. I think the different definitions need to be sourced and compared, and depending on how it looks maybe those articles should be merged. But one is more electronic and the other more general, so probably not. [[User:Dicklyon|Dicklyon]] 08:10, 2 January 2007 (UTC)

== Revert to [[Snell's Law]] ==

Care to explain? Just curious is all.. the introduction there was referenced in the previous version.. Not pointing fingers or being nasty, i'm just generally curious. [[User:JSpudeman|James S]] 19:14, 4 January 2007 (UTC)
:I have to say, i'm happy to see another wikipedian who actually posts comments on talk pages -- you have my appreciation. I'll add in the references, and generally clean up the introduction so it's grammatically correct. I've bought myself an optics book and it too says that Snell's law is, indeed, the full formula specified further down the page on the article. I've checked it out in several physics books i've got and they generally resolve it the same.

:I've not found a book yet which lists the actual formula as it was specified by Willebrord Snellius or other contrbutors. Generally, though, they do agree that it's defined as the relationship between the angle of refraction and the refractive indeces of two materials, and is generally re-arranged to find incident/refractive angles. Still, how true this is based upon the original formula(e) is unknown to me. Cheers, [[User:JSpudeman|James S]] 19:31, 4 January 2007 (UTC).

::Let's take it back to [[Talk:Snell's law]]. [[User:Dicklyon|Dicklyon]] 22:14, 4 January 2007 (UTC)

== Question ==

Hello. I know that you have a lot of experience with Wikipedia so I would like to come to you with a question. I was looking at the [[Deere & Company]] page and in the external links there is a link to http://www.tractordata.com/td/johndeere.html - According to the guidelines for external links people should only place official links and that is not official. Would I be right in taking that link off? I don't want to do it if you think that would not be appropriate. As you know I used to add things to Wikipedia that would make me be considered as a [[Vandal]], however, I would like you to know that I am not at all like that anymore. If you don't mind I would like to come to you with my questions and hope that we will be able to get along! Thanks [[User:Eric outdoors|Eric]] 02:43, 5 January 2007 (UTC)

:The critera are not so strict, usually. See [[WP:EL]]. If in doubt, mention it on the article's talk page and seek the advice of more experienced editors of that article. It looks to me like probably the work of guy who makes lots of info site to try to get some advertising revenue, but I'm not sure. [[User:Dicklyon|Dicklyon]] 03:00, 5 January 2007 (UTC)

::I looked at the history of the page and there is not really anyone that really makes a lot of consistent edits on the page. The page is really about the John Deere Company NOT John Deere tractors so i think that link does not belong there. What should I do in a situation which there are no consistent editors to ask. Should I just go ahead and remove the link? Thanks for your time [[User:Eric outdoors|Eric]] 03:11, 5 January 2007 (UTC)

:::Click on "discussion". Add a new section at the bottom to say what you're intending to do, and see if anyone objects; you don't need to address anyone in particular. Or, if you're confident enough, just be bold and do it, and see if anyone objects. [[User:Dicklyon|Dicklyon]] 03:16, 5 January 2007 (UTC)

::::Thank You!

==Read it and weep==
Observe:

They are used to denote possession, for example:
the dog's bone
the company's logo
Jones's bakery (but Joneses' bakery if owned by more than one Jones)

... but please note that the possessive form of it does not take an apostrophe any more than ours, yours or hers do

the bone is in its mouth

... however, if there are two or more dogs, companies or Joneses in our example, the apostrophe comes after the 's':
the dogs' bones
the companies' logos
Joneses' bakeries {[http://www.apostrophe.fsnet.co.uk/ Source])

As you can plainly see, I am '''''NOT''''' making this up. [[User:TomStar81|TomStar81]] ([[User talk:TomStar81|Talk]]) 01:31, 7 January 2007 (UTC)

:But we were not talking about multiple [[Fort Bliss]]es, just one. See [[Apostrophe#Singulars]]. [[User:Dicklyon|Dicklyon]] 01:52, 7 January 2007 (UTC)

:Yeah, I see that now. This was more of a "yes, there is such a thing as an apostraphe with no s" than an "I'm right and your wrong, so shove it" kind of thing. Ordinarilly I do not argue with, or revert, gramatical changes (or spelling changes, for that matter) in articles that I create, wrote, or moniter becuase I know that my grammar and spelling suck. In this one case though, I remembered hereing something about not adding apostrophes after the letter s if the word being apostrosized ended in an s, although it does appear that I am, in fact, in the wrong. Sorry if I offended you, as that was not my intention, and thank you for catching the mistake. [[User:TomStar81|TomStar81]] ([[User talk:TomStar81|Talk]]) 02:46, 7 January 2007 (UTC)

::No offense taken. Glad I could teach you something. [[User:Dicklyon|Dicklyon]] 05:09, 7 January 2007 (UTC)

== Popups ==

You might want to be careful what you use the reverting feature of popups for. You appear to be using it to revert good faith edits sometimes, and if done at the wrong time that can make things a bit messy. --[[User:Deskana|Deskana]] [[User talk:Deskana|(For Great Justice!)]] 18:19, 7 January 2007 (UTC)

:Can you provide an example? [[User:Dicklyon|Dicklyon]] 18:22, 7 January 2007 (UTC)

::[http://en.wikipedia.org/w/index.php?title=Golden_rectangle&diff=prev&oldid=99128539 This]. [http://en.wikipedia.org/w/index.php?title=George_W._Bush&diff=prev&oldid=99134496 And this]. It wasn't vandalism, seems like a good faith edit. Doesn't mean it didn't need reverting. It's similar to the reasons that administrators aren't supposed to use the rollback function when reverting good faith edits. --[[User:Deskana|Deskana]] [[User talk:Deskana|(For Great Justice!)]] 18:25, 7 January 2007 (UTC)

:::OK, got it. I'll use undo and a comment next time. [[User:Dicklyon|Dicklyon]] 18:55, 7 January 2007 (UTC)

::::Thanks. :-) --[[User:Deskana|Deskana]] [[User talk:Deskana|(For Great Justice!)]] 20:11, 7 January 2007 (UTC)

==[[Rolf Rodenstock]]==
I have added a "{{[[Template:prod|prod]]}}" template to the article [[Rolf Rodenstock]], suggesting that it be deleted according to the [[Wikipedia:Proposed deletion|proposed deletion]] process. All contributions are appreciated, but I don't believe it satisfies Wikipedia's criteria for inclusion, and I've explained why in the deletion notice (see also "[[Wikipedia:What Wikipedia is not|What Wikipedia is not]]" and [[Wikipedia:Deletion policy|Wikipedia's deletion policy]]). Please either work to improve the article if the topic is worthy of inclusion in Wikipedia, or, if you disagree with the notice, discuss the issues at [[Talk:Rolf Rodenstock|its talk page]]. Removing the deletion notice will prevent deletion through the proposed deletion process, but the article may still be sent to [[Wikipedia:Articles for deletion|Articles for Deletion]], where it may be deleted if consensus to delete is reached, or if it matches any of the [[Wikipedia:Criteria for speedy deletion|speedy deletion criteria]]. [[User:172.144.122.155|172.144.122.155]] 04:41, 9 January 2007 (UTC)

== Overexposure / Golden Hour Photography ==

Thanks for rewriting this - you did a much better job than I did. Good writing and fluid language are important, I enjoy them, but I can't produce it. The article reads a lot better now. [[User:ForrestCroce|ForrestCroce]] 07:48, 9 January 2007 (UTC)
==License tagging for Image:CheatSheetEV.png==
Thanks for uploading [[:Image:CheatSheetEV.png]]. Wikipedia gets thousands of images uploaded every day, and in order to verify that the images can be legally used on Wikipedia, the source and copyright status must be indicated. Images need to have an [[Wikipedia:Image copyright tags|image tag]] applied to the [[Wikipedia:Image description page|image description page]] indicating the copyright status of the image. This uniform and easy-to-understand method of indicating the license status allows potential re-users of the images to know what they are allowed to do with the images.

For more information on using images, see the following pages:
* [[Wikipedia:Image use policy]]
* [[Wikipedia:Image copyright tags]]

This is an automated notice by [[User:OrphanBot|OrphanBot]]. If you need help on selecting a tag to use, or in adding the tag to the image description, feel free to post a message at [[Wikipedia:Media copyright questions]]. 08:07, 10 January 2007 (UTC)

== Transistor images ==

Hi, i have changed the transistor image on the page [[transistor]] back to the newly photographed version. The old is too shiny and 3 of 6 shapes are almost never used. (And I do not consider the red background to be nice.) I think it is useful to let the reader see how ''real'' transistor looks and what size it has. It is a bit frustrating, that the change was reverted without plausible reason... --[[User:FDominec|FDominec]] 15:51, 12 January 2007 (UTC)

: And I am going to make new (more contrast and simplier) version of this
image.--[[User:FDominec|FDominec]] 21:45, 12 January 2007 (UTC)
== Rodenstock==
There are quite a number of people prodding and even speedying technical articles which they do not understand. It's hard to catch them, and I've been commenting on the speedy talk page.'''[[User:DGG|DGG]]''' 05:32, 14 January 2007 (UTC)

:Oh, well, part of the game. I just prodded one myself: [[Hendy's Law]]. [[User:Dicklyon|Dicklyon]] 05:42, 14 January 2007 (UTC)

== No personal attacks ==

{{{{{subst|}}}#if:Talk:Standard test image|With regards to your comments on [[:Talk:Standard test image]]: }}Please see Wikipedia's [[Wikipedia:No personal attacks|no personal attacks]] policy. Comment on ''content'', not on contributors; personal attacks damage the community and deter users. Note that continued personal attacks may lead to [[Wikipedia:Blocking policy|blocks]] for disruption. Please [[Wikipedia:Staying cool when the editing gets hot|stay cool]] and keep this in mind while editing. Thank you.  --[[User:Oden|Oden]] 02:51, 15 January 2007 (UTC)

:With regard to [http://en.wikipedia.org/w/index.php?title=Talk:Standard_test_image&curid=3847006&diff=100787752&oldid=100779363 this diff]. --[[User:Oden|Oden]] 02:51, 15 January 2007 (UTC)

::OK; I'll edit my comment to a cooler version. [[User:Dicklyon|Dicklyon]] 02:53, 15 January 2007 (UTC)

== large blocks of quoted text ==

Hello, and [[Wikipedia:Welcome, newcomers|welcome to Wikipedia]]. We appreciate your {{#if:Lenna|contributions to the [[:Lenna]] article|contributions}}, but for legal reasons, we cannot accept [[Wikipedia:Copyrights|copyrighted]] text or images borrowed from other web sites or printed material, and as a consequence, your addition will most likely be deleted.

Feel free to re-submit a new version of the article. You may use external websites as a source of ''information'', but not as a source of ''sentences''. This part is crucial: ''say it in your own words''.

If the external website belongs to you, and you want to allow Wikipedia to use the text — which means allowing other people to modify it — then you must include ''on the external site'' the statement "I, (name), am the author of this article, (article name), and I release its content under the terms of the [http://www.gnu.org/copyleft/fdl.html GNU Free Documentation License], Version 1.2 and later."

You might want to look at [[Wikipedia:Policies and guidelines|Wikipedia's policies and guidelines]] for more details, or ask a question [[Wikipedia:Village pump (assistance)|here]]. You can also leave a message on my talk page. --[[User:Oden|Oden]] 08:01, 15 January 2007 (UTC)

:What template did you subst that from? I don't find anything about "quote" on the referenced pages. The paragraphs I quoted are certainly not large blocks of text, and the largest is from a magazine, not a web page. As I pointed out in the talk page there, it makes little sense to try to paraphrase a second-hand story of a recollection and try to pass it off as verifiable information; much better to just quote the story and attribute the source; it's not a big part of the referenced publication, just a bit for historical commentary. [[User:Dicklyon|Dicklyon]] 08:06, 15 January 2007 (UTC)

::I have sent the matter to [[Wikipedia:Administrators' noticeboard/Incidents]] ([Wikipedia:Administrators%27_noticeboard/Incidents#Lenna_and_quotes here]) since the article is in violation of our [[WP:FUC|fair use policy]]. --[[User:Oden|Oden]] 08:24, 15 January 2007 (UTC)

:::Thanks. I will respect their opinion on this. [[User:Dicklyon|Dicklyon]] 08:26, 15 January 2007 (UTC)

== Difference between "what he said" and "what is easier to understand" ==

Just wanted to address a little point, which nags me a little, but i'm just addressing it. The main difference is that i agree with you all points when you're talking about referencing almost "to the letter" of what a particular physicist/mathematician said.. particularly because it gives a greater understanding of the topic, amongst other things.

Then again, i remind myself that it's the Wikipedia, and not everything that physicists say is very easy to understand by other non-physicists, because we're not poets or writers, but physicists. Sometimes it's easier to take on board what a physicist wrote, and expand upon it so it makes more sense to others reading the article for the first time than just write a half-coherent sentence that is 100% compliant.

Not to do with the S/L article, just a little bit of advice, perhaps. [[User:JSpudeman|James S]] 20:22, 15 January 2007 (UTC)

:Sorry, I've editted a few hundred articles in the last day, and I don't know what article you mean to refer to by S/L or what exactly you're talking about. Care to get specific? [[User:Dicklyon|Dicklyon]] 20:58, 15 January 2007 (UTC)

:Oh, I see from your contribs that you mean [[Snell's law]]. I still don't get your point, though. Can you refer to an edit or a quote or whatever? [[User:Dicklyon|Dicklyon]] 21:02, 15 January 2007 (UTC)

::Apologies. What i'm saying is, even though a text by Decartes, Huygens, or any other optician may describe snell's law in a definite way, it might not be ideal to include it in the wikipedia article exactly as it is stated, because there's a different audience being addressed. On one hand, Huygens or Descartes would be publishing work specifically for it to be read by physicists in the majority, whereas the wikipedia aims to allow anyone to read it.

:In other words -- we should allow anyone who reads the article to understand it, physicist, poet, or otherwise. Sorry if my responses are somewhat cryptic, I'm not really a person who likes to post on the wikipedia talk pages, or generally reply on forums or internet-based chatter. [[User:JSpudeman|James S]]
::Well, if you want to make a point you do need to speak up. I've just re-editted your changes to the article to make it more correct. I agree it needs to be accessible in modern terms, which is why I'm not quoting the original Latin and French. But it also needs to not be perverted to where what the law is is lost. See if you like what I've done, even if perhaps it doesn't necessarily make Snell's law accessible to the average poet. [[User:Dicklyon|Dicklyon]] 21:42, 15 January 2007 (UTC)
:::Well, technically, i dont have a "voice" on the wikipedia until i make a spoken version of the article :-P. But yes, the edits are good. Similarly, i'd like to think you're not adding the original latin or french because this is the english wikipedia.
:::Also, yes. No perversion is good perversion. [[User:JSpudeman|James S]] 21:59, 15 January 2007 (UTC)
::::How poetic. [[User:Dicklyon|Dicklyon]] 22:04, 15 January 2007 (UTC)

Come off it. [[User:JSpudeman|James S]] 22:21, 15 January 2007 (UTC)

{| style="text-align:center; font-size:14px;" align="right"
|[[Image:Dicklyon.jpg|150px]]
Shakespeare
|[[Image:Shakespeare.jpg|165px]]
Dick Lyon
|}
:Yes, the resemblance is striking. Swapped at birth. [[User:Dicklyon|Dicklyon]] 23:06, 15 January 2007 (UTC)

== Infoboxes for optics articles ==

Do you think it'd be a good idea to have an infobox for optics, which contains formulae info, etc? —The preceding [[Wikipedia:Sign your posts on talk pages|unsigned]] comment was added by [[User:JSpudeman|JSpudeman]] ([[User talk:JSpudeman|talk]] • [[Special:Contributions/JSpudeman|contribs]]) 14:15, 16 January 2007 (UTC).

:I don't know. I'm not a big fan of infoboxes. They tend to be sort of limiting, hard to improve or extend. What do you have in mind exactly? [[User:Dicklyon|Dicklyon]] 16:07, 16 January 2007 (UTC)

::Well, i'm not too sure how it'd look, but it could be something small that lists related concepts in optics. I'm with you though, i'm not that big a fan of them if they don't look too good, but i think a nice little infobox could make it easier to browse around optics articles. Also.. i found out there's [[Wikipedia:WikiProject Optics]].. interested in joining? [[User:JSpudeman|James S]] 16:39, 16 January 2007 (UTC)
::I'll take a look. [[User:Dicklyon|Dicklyon]] 16:42, 16 January 2007 (UTC)

== Opinion, if you please. ==

[[Image:Refraction_reflection_as_wavelength.png|thumb|300px|left|Well, it's worth a shot, huh.]]
I've just managed to try and mangle together a picture illustrating refraction, partial reflection and marked it up with angles relevant to snell's law. I'm not the best graphic artist, but i think i did alright just using KOffice and some patience :-) The refraction is a little iffy, but it's alright i guess. [[User:JSpudeman|James S]] 21:31, 17 January 2007 (UTC)
[[Image:Huygens Refracted Waves.png|thumb|200px|right|Huygens 1678 refraction.]]
:It's a good start, but slightly mangled as you say. You probably should get the theta r to line up with the refracted lines, and get them to line up square with each other. If I were doing this, I'd probably write a matlab program to draw the lines. Otherwise, it may just take a lot of care in drawing. What are you using? Can you make an svg of it? By the way, take a look at how Huygens drew it (refraction part only). [[User:Dicklyon|Dicklyon]] 22:23, 17 January 2007 (UTC)

Well, i can try to make it into a SVG, but i'm not the best at graphical tasks. I didn't include the huygens wave "markup" because it's difficult for me to do that without mangling the image even more. The image currently needs to have the incidence and reflection at the same angle, other things cleaned up, which is a lot easier when it's done with lines, as there's a few positioning problems with the software at the moment.. [[User:JSpudeman|James S]] 10:14, 18 January 2007 (UTC)

The Green Mile

2007-01-18T00:03:28Z

JSpudeman: Please boss.. lets use grammar correctly.

*See [[The Green Mile (book)]] for the [[novel|serial novel]] by [[Stephen King]].
*See [[The Green Mile (film)]] for the film based on the Stephen King novel starring [[Michael Clarke Duncan]] and [[Tom Hanks]].
{{disambig}}

[[de:The Green Mile]]

Snell's law

2007-01-18T00:00:41Z

JSpudeman: Just a few minor changes.. we need an image to illustrate the critical angle.

[[Image:Snells law.svg|thumb|300px|[[Refraction]] of light at the interface between two media of different [[refractive index|refractive indices]], with n2 > n1. Since the velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.]]

In [[optics]] and [[physics]], '''Snell's law''' (also known as '''Descartes' Law''' or the '''law of refraction'''), is a [[mathematical formula|formula]] used to describe the relationship between the angles of incidence and refraction, when referring to light or other [[wave]]s, passing through a boundary between two different [[isotropic]] [[medium (optics)|media]], such as air and glass. The law says that the ratio of the [[sine]]s of the angles of incidence and of refraction is a constant that depends on the media.

In optics, the law is used in [[ray tracing]] to compute the angles of [[angle of incidence|incidence]] or [[angle of refraction|refraction]], and in experimental optics to find the [[refractive index]] of a material.

Named for one of its discoverers, [[Willebrord Snellius]], Snell's law follows from [[Pierre de Fermat]]'s [[Fermat's principle|principle of least time]], which states that the ratio of the [[sine]]s of the angles of incidence and refraction is equal to the ratio of [[velocities]] in the two media, or equivalently the inverse ratio of the indices of refraction:

{| cellspacing="10"
|<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{n_2}{n_1}</math>
| or
|<math>n_1\sin\theta_1 = n_2\sin\theta_2\ </math>
|}

== History ==
[[Image:Snell Law of Sines 1837.png|thumb|right|300px|An 1837 view of the history of "the Law of the Sines"<ref>William Whewell, ''History of the Inductive Science from the Earliest to the Present Times'', London: John H. Parker, 1837.</ref>]]
Snell's law was first discovered and described by [[Ibn Sahl]] in a manuscript written c.[[984]],<ref>{{cite journal | author=Rashed, Roshdi | title= A pioneer in anaclastics: Ibn Sahl on burning mirrors and lenses | journal= [[Isis (journal)|Isis]]| year= 1990| volume= 81| pages= 464–491 |doi=10.1086/355456}}</ref> who used it to work out the shapes of lenses that focus light with no geometric aberrations, known as [[anaclastic lens]]es. It was discovered again by [[Thomas Harriot]] in [[1602]],<ref>{{cite journal | author=Kwan, A., Dudley, J., and Lantz, E. | title=Who really discovered Snell's law? | journal=[[Physics World]] | year=2002 | volume=15 | issue=4 | pages=64 |url=http://physicsworldarchive.iop.org/index.cfm?action=summary&doc=15%2F4%2Fphwv15i4a44%40pwa-xml&qt=}}</ref> who did not publish his work.

In [[1621]], it was discovered yet again by Willebrord Snel, in a mathematically equivalent form, but unpublished during his lifetime. [[René Descartes]] independently derived the law using heuristic momentum conservation arguments in terms of sines in his [[1637]] treatise ''[[Discourse on Method]]'' (though detractors such as Fermat accused Descartes of working toward the already known answer with sophistic reasoning), and used it to solve a range of optical problems. Rejecting Descartes' solution, Pierre de Fermat arrived at the same solution based solely on his principal of least time.

In [[French language|French]], Snell's Law is called "la loi de Descartes" or "loi de Snell-Descartes."

== Explanation ==
Snell's law is used to determine the direction of light rays though refractive media with varying indices of refraction. The indices of refraction of the media, labeled <math>n_1,n_2</math> and so on, are used to represent the factor by which light is "slowed down" within a refractive medium, such as glass or water, compared to its velocity in a vacuum.

As light passes the border between media, depending upon the relative refractive indices of the two media, the light will either be refracted to a lesser angle, or a greater one. These angles are measured with respect to the ''normal line'', represented perpendicular to the boundary. In the case of light traveling from air into water, light would be refracted towards the normal line, due to the fact that the light is slowed down in water; light traveling from water to air would refract away from the normal line.

Refraction between two surfaces is also referred to as ''reversible'' due to the fact that if all conditions were identical, the angles would be the same for light propagating in the opposite direction.

Snell's law is only generally true for isotropic or specular media (such as [[glass]]). In [[anisotropic]] media such as some [[crystal]]s, [[birefringence]] may split the refracted ray into two rays, the ''ordinary'' or ''o''-ray which follows Snell's law, and the other ''extraordinary'' or ''e''-ray which may not be co-planar with the incident ray.

When the light or other wave involved is monochromatic, that is, of a single frequency, Snell's law can also be expressed in terms of a ratio of wavelengths in the two media, λ1 and λ2:

:<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{\lambda_1}{\lambda_2}</math>

=== Total internal reflection and critical angle ===
[[Image:Refraction internal reflection diagram.PNG|thumb|220px|right|An example of the angles involved within total internal reflection.]]
When light moves from a dense to a less dense medium, such as from water to air, Snell's law cannot be used to calculate the refracted angle when the resolved sine value is higher than 1. At this point, light is reflected in the incident medium, known as internal reflection. Before the ray totally internally reflects, the light refracts at the '''critical angle'''; it travels directly along the surface between the two refractive media, without a change in phases like in other forms of optical phenomena.

As an example, a ray of light is incident at <math>50^o</math> towards a water–air boundary. If the angle is calculated using Snell's Law, then the resulting sine value will not invert, and thus the refracted angle cannot be calculated:

:<math>\theta_2 = \sin^{-1} (\frac{n_1}{n_2}\sin\theta_1) = \sin^{-1} (\frac{1.333}{1.000}0.766) = \sin^{-1} 1.021</math>

Snell's Law cannot calculate such angles because there is no refracted outgoing ray.

In order to calculate the critical angle, let <math>\theta_2 = 90^o</math> and solve for <math>\theta_\mathrm{crit}</math>:

:<math>\theta_{\mathrm{crit}} = \sin^{-1} \left( \frac{n_2}{n_1} \right)</math>

When θ1 > θcrit, no refracted ray appears, and the incident ray undergoes [[total internal reflection]] from the interface medium.

=== Derivations ===
Snell's law may be derived from [[Fermat's principle]], which states that the light travels the path which takes the least time. By taking the [[derivative]] of the [[optical path length]], the [[stationary point]] is found giving the path taken by the light (though it should be noted that the result does not show light taking the least time path, but rather one that is stationary with respect to small variations as there are cases where light actually takes the greatest time path, as in a spherical mirror).

Alternatively, Snell's law can be derived using interference of all possible paths of light wave from source to observer—it results in destructive interference everywhere except extrema of phase (where interference is constructive)—which become actual paths. In a classic analogy by [[Richard Feynman]], the area of lower refractive index is replaced by a beach, the area of higher refractive index by the sea, and the fastest way for a rescuer on the beach to get to a [[drowning]] person in the sea is to run along a path that follows Snell's law.

Another way to derive Snell’s Law involves an application of the general [[boundary conditions]] of [[Maxwell equations]] for [[electromagnetic radiation]].

== Uses ==
=== Calculating refractive indices ===

In the diagram on the right, two media of refractive indices ''n''1 (on the left) and ''n''2 (on the right) meet at a surface or interface (vertical line). ''n''2 > ''n''1, and light has a slower [[phase velocity]] within the second medium.

A light ray '''PO''' in the leftmost medium strikes the interface at the point '''O'''. From point '''O''', we project a straight line at right angles to the line of the interface; this is known as the [[Surface normal|normal]] to the surface (horizontal line). The angle between the normal and the light ray '''PO''' is known as the ''angle of incidence'', θ1.

The ray continues through the interface into the medium on the right; this is shown as the ray '''OQ'''. The angle it makes to the normal is known as the ''angle of refraction'', θ2.

:<math>n_1 \sin\theta_1 = n_2 \sin\theta_2 </math> or <math>\sum_{k=x,y}^N x=n_x\sin\theta_x,n_y \sin\theta_y</math>
:<math>\frac{n_1}{n_2} = \frac{\sin\theta_2}{\sin\theta_1}</math>
Note that, for the case of θ1 = 0° (i.e., a ray perpendicular to the interface) the solution is θ2 = 0° regardless of the values of ''n''1 and ''n''2-- a ray entering a medium perpendicular to the surface is never bent.

The above is also valid for light going from a dense to a less dense medium; the symmetry of Snell's law shows that the same ray paths are applicable in opposite direction.

A qualitative rule for determining the direction of refraction is that the ray in the denser medium is always closer to the normal. An analogy often used to remember this is done by visualizing the ray as a car crossing the boundary between asphalt (the less dense medium) and mud (the denser medium). Depending on the angle, either the left wheel or the right wheel of the car will cross into the new medium first, causing the car to swerve.

=== Vector form ===

Given a normalized ray vector '''v''' and a normalized plane normal vector '''p''', one can work out the normalized reflected and refracted rays:

:<math>\cos\theta_1=\mathbf{v}\cdot\mathbf{p}</math>
:<math>\cos\theta_2=\sqrt{1-\left(\frac{n_1}{n_2}\right)^2\left(1-\left(\cos\theta_1\right)^2\right)}</math>
:<math>\mathbf{v}_{\mathrm{reflect}}=\mathbf{v}-\left(2\cos\theta_1\right)\mathbf{p}</math>
:<math>\mathbf{v}_{\mathrm{refract}}=\left(\frac{n_1}{n_2}\right)\mathbf{v} + \left(\cos\theta_2 - \frac{n_1}{n_2}\cos\theta_1\right)\mathbf{p}</math>
Note: <math>\mathbf{v}\cdot\mathbf{p}</math> must be positive.

The cosines may be recycled and used in the [[Fresnel equations]] for working out the intensity of the resulting rays. During total internal reflection an [[evanescent wave]] is produced, which [[exponential decay|rapidly decays]] from the surface into the second medium. Conservation of energy is maintained by the circulation of energy across the boundary, averaging to zero net energy transmission.

==Dispersion==

In many wave-propagation media, wave velocity changes with frequency or wavelength of the waves; this is true of light propagation in most transparent substances other than a vacuum. These media are called dispersive. The result is that the angles determined by Snell's law also depend on frequency or wavelength, so that a ray of mixed wavelengths, such as white light, will spread or disperse. Such dispersion of light in glass or water underlies the origin of [[rainbow]]s, since different wavelenghts appear as different colors.

In optical instruments, [[dispersion (optics)|dispersion]] leads to [[chromatic aberration]], a color-dependent blurring that sometimes is the resolution-limiting effect. This was especially true in [[refracting telescope]]s, before the invention of achromatic objective lenses.

==See also==

* [[Fresnel equations]]
* [[Reflection (physics)|Reflection]]
* [[Refraction]]
* [[Total internal reflection]]
* [[Evanescent wave]]

==References==

<references />

== External links ==

* [http://mintaka.sdsu.edu/GF/explain/optics/discovery.html Discovery of the law of refraction]

[[Category:Geometrical optics]]
[[Category:Introductory physics]]
[[Category:Eponymous laws]]

[[cs:Snellův zákon]]
[[de:Snelliussches Brechungsgesetz]]
[[es:Ley de Snell]]
[[fr:Lois de Snell-Descartes]]
[[it:Legge di Snell]]
[[he:חוק סנל]]
[[nl:Wet van Snellius]]
[[ja:スネルの法則]]
[[no:Snells brytningslov]]
[[pl:Prawo Snelliusa]]
[[ru:Закон Снелла]]
[[sl:Lomni zakon]]
[[sv:Snells lag]]
[[zh:光的折射定律]]

Imagine (TV series)

2007-01-17T22:44:31Z

JSpudeman: WP

'''''Imagine''''' is a wide ranging arts series first broadcast on [[BBC One]] in [[2003]]. Hosted and executive produced by [[Alan Yentob]] the show is currently in its 8th series. Episodes have been directed by [[Geoff Wonfor]], [[Lucy Blakstead]] and [[Roger Parsons]].
The current series includes a programme about the internet and features an interview with the co-founder of Wikipedia, Jimmy Wales.

'''Series 1''' (from [[June 11]] [[2003]]):
* The [[Charles Saatchi|Saatchi]] Phenomenon
* [[Barbara Hepworth]]: Shapes Out of Feelings
* The [[Hip hop music|Hip Hop]] Generation
* [[Stella McCartney|Stella]]'s Story
* [[Carlos Acosta]]: The Reluctant Ballet Dancer
* [[James Cook#Third voyage (1776-1779)|The Potrait of Omai]]
* [[John Mortimer]]: Owning Up at 80

'''Series 2''' (from [[November 12]] [[2003]]):
* The Voice of [[Bryn Terfel]]
* A Funny Business - A look at [[United Kingdom|UK]] and [[United States of America|US]] [[sitcom]]s
* Entertaining [[John Soane|Mr Soane]]
* The World According to [[Martin Parr|Parr]]
* From Pencils to Pixels - celebrates the phenomena of the [[animation|animated]] feature [[film]]
* An A-Z of the [[Oxford English Dictionary|OED]]

'''Series 3''' (from [[November 24]] [[2004]]):
* [[Arthur Miller]]: Finishing the Picture
* Beautiful Dreamer: [[Brian Wilson]]'s Smile
* [[Bruce Nauman]]: The Godfather of Modern Art
* [[Marlon Brando|Brando]]
* [[Antonio Pappano]]: A Year at the Opera

'''Series 4''' (from [[May 11]] [[2005]]):
* A Short History of Tall Buildings (3 parts)

'''Series 5''' (from [[June 22]] [[2005]]):
* Fantastic Mr [[Roald Dahl|Dahl]]
* [[Frida Kahlo]]
* Being a Concert Pianist

'''Series 6''' (from [[November 23]] [[2005]]):
* [[Edward Elgar|Elgar]] and the Missing Concerto
* [[Amos Oz]]: The Conscience of [[Israel]]
* [[Chuck Close]], Close Up
* Rhythm Is It!

'''Series 7''' (from [[January 17]] [[2006]])
* Sweet Home [[New Orleans]] - examining the city's musical heritage
* [[Andy Warhol|Warhol]] Denied
* A Funny Thing Happened On the Way to the Studio
* Sitting Comfortably - traces the changing styles of the modern chair

'''Series 8''' (from [[May 23]] [[2006]])
* Being [[Hamlet]]
* Yusuf, the Artist Formerly Known As [[Cat Stevens]]
* The Ingenious [[Thomas Heatherwick]]
* www.herecomeseverybody.co.uk - A history of the [[World Wide Web]] (included the [[Wikipedia]])

==External link==
* {{imdb title|id=0237968|title=Imagine}}

[[Category:BBC television documentaries]]

Amarok (software)

2007-01-17T22:26:01Z

JSpudeman: References to be added shortly.. interview on wikinews shortly with Mark Kretschmann

{{Infobox_Software|
name = Amarok
|logo=[[Image:amarok-icon.png|48px]]
|screenshot = [[Image:amaroK_stable.png|250px]]
|caption = A screenshot of Amarok, showing the player window and playlist manager.
|developer = The Amarok Team
| latest_release_version = 1.4.4
| latest_release_date = [[October 30]] [[2006]]
| latest_preview_version = 
| latest_preview_date =
|operating_system = [[Unix-like]]
|genre = [[Audio player (software)|Audio player]]
|license = [[GNU General Public License|GPL]]
|website = [http://amarok.kde.org/ amarok.kde.org]
}}
'''Amarok''' (formerly known as '''amaroK''') is a [[free software]] music player for [[Linux]] and other [[Unix-like|varieties of Unix]]. It makes use of core components from the [[KDE]] desktop environment, but is released independently of the central KDE release cycle, and is developed with a desktop-agnostic policy.

Despite the fact that Amarok uses wolf-based artwork, and that the name "amarok" or "amaroq" literally refers to the [[Inuktitut]] word for "[[wolf]]", it was originally named after the album ''[[Amarok (album)|Amarok]]'' by [[Mike Oldfield]]. The 1.2 release originally had a [http://www.deviantart.com/deviation/13944216/ wolf icon], but this was later withdrawn due to similarity with the logo of [[WaRP Graphics]] Inc. Amarok's wolf logo has now been modified sufficiently so as not to infringe on WaRP's trademark logo, and re-instated.

Originally it was named '''amaroK''', with an [[upper-case]] "K" related to KDE application [[naming conventions]]. It was, however, renamed to Amarok in June 2006 after intensive discussions on usability at a KDE-based [[business conference|conference]], K3M, in May the same year.

== History ==
The project was originally started by [[Mark Kretschmann]] as a means of bettering [[XMMS]] due to several usability problems, which interfered with the addition of new files to the playlist due to several user inferface elements existing for one task. The original amaroK was created based upon the idea of a two-pane interface seen in [[midnight commander]], and the first version of the software released solely by Kretschmann, was based upon the ideal of allowing users to drag-and-drop music into an interface in which the playlist was displayed on the right and information on the left.

After the initial release of amaroK, several developers joined the project to form the "Three M's" the first of whom was Max Howell, who acted as an interface designer and programmer for the project, alongside Muesli, who also provided user interface insight and programming for the early versions.

==Development goals==
Amarok's tagline is "Rediscover Your Music", and its development is based around this ideology. Amarok's core features such as the unique "context browser", integrated Wikipedia lookup and lyrics download help users to find new music, and to learn more about the music they have. Amarok also features integration with [[last.fm]], giving users suggestions about what to listen to next and which artists may fit their mood, as well as with [[Magnatune]], allowing no-cost full listening of all the music in their catalog, and DRM-free purchasing.

==Features==

'''Basic Uses and Functions'''

Amarok serves many functions rather than just playing music files. For example, Amarok can be used to organize a library of music into folders according to genre, artist, and album, can edit tags attached to most music formats, associate album art, attach lyrics, and automatically "score" music as you play it. Thus, the first run of Amarok can be daunting for some users. Users that find the interface difficult to navigate due to the many features may hide some features (such as by closing tabs) but may simply prefer a simpler audio player. The abundance of features has also attracted some criticism that Amarok is resource-intensive or "bloated."

Although a more technical list of features is listed below, here are the primary functions or uses for Amarok:
* Playing media files in various formats including but not limited to (depending on the setup) [[FLAC]], [[Ogg]], [[MP3]], [[AAC]], [[WAV]], [[WMA]], and [[Musepack]]. Note that Amarok will NOT play DRM'd or "protected" digital music files such as those purchased from the [[iTunes]] Music Store.
* Tagging digital music files (currently [[Ogg]], [[WMA]], [[AAC]], [[MP3]], and [[RealMedia]]).
* Associating cover art with a particular album, and retrieving the cover art from [[Amazon.com]]
* Creating and editing playlists, including smart and dynamic playlists. The dynamic playlists can use such information as the "score" given to a song by an Amarok script, and the playcount which is stored with the song.
* Syncing, retrieving, playing, or uploading music to your digital music player, such as an [[iPod]] or [[Creative Zen]].
* Displaying artist information from Wikipedia and retrieving song lyrics.
* [[Last.fm]] support, including submitting played tracks (including those played on some digital music players) to Last.fm, retrieving similar artists, and playing Last.fm streams.
* Podcasting

The current version of Amarok, 1.4.4 introduced the integration of the non-[[DRM]] digital music store, [[Magnatune]] so users can purchase music in [[Ogg]], [[FLAC]], [[WAV]] and [[MP3|MP3 VBR]] formats.

Note that some of these features depend on other programs or libraries that must be on your computer to operate. Furthermore, some of the features, such as support for newer iPods and AAC tag editing may only be accessible if Amarok is complied from source, depending on how a particular distribution packages the software.

Additionally, although Amarok can be used with most Linux desktop environments, Amarok uses KDElibs and QT, so Linux users running environments such as [[GNOME]] rather than [[KDE]] will notice some quirks that are mostly cosmetic. Other projects, such as [[Exaile]] have been initiated to attempt to bring Amarok's functionality to a gtk-based program. But even under an environment like [[GNOME]] Amarok retains all of its functionality.

'''More Technical Features'''

* Two main windows - playlist browser and player window (latter is optional).
* [[Systray]] (panel notification area) icon support.
* Song collection, which includes specific folders on the filesystem.
** Can be stored in an internal [[SQLite]] database, or external [[MySQL]] or [[PostgreSQL]] database.
** Songs can be rated both dynamically (based on how much the song is played) and by hand (giving rating of 1-5 stars to the song).
** Amarok File Tracking (since 1.4.3): Stores file checksum in the collection. This allows the file be moved around in the filesystem without Amarok losing track of the song statistics. (In betas, this feature was called Advanced Tag Features, and instead stored unique identifier in the song tags.)
** Collection filter (newest songs, highest rated, most played, etc.).
* Playback options:
** 10-band graphic [[equalization|equalizer]].
** Crossfading (for GStreamer, Xine and aRts).
** [[Gapless playback]] (MP3 and other codecs).
* Support for syncing, reading, and writing to the following digital music players: [[iPod]], [[iRiver]] iFP, [[Creative NOMAD]], [[Creative Zen]], [[Media Transfer Protocol|MTP]], [[Rio Karma]] and [[USB]] devices with [[VFAT]] (generic MP3 players) support.
* Support for several audio engines. The audio engine also dictates which media types Amarok can play.
** [[aRts]] (unmaintained since 1.3, and unlikely to return)
** [[GStreamer]] (disabled in 1.4 due to a lack of maintainer)
** [[Helix project|Helix]]
** [[Media Application Server]] (MAS)
** [[Network-Integrated Multimedia Middleware]] (NMM)
** [[Xine|xine-lib]]
** Uses [[TagLib]] for tags.
** [[MusicBrainz]] support.
** Amarok can be controlled via [[DCOP]].
** [[Ruby programming language|Ruby]] can be used for scripting, for example, when writing lyrics fetching plugins.
** Support for [[Digital Audio Access Protocol]] and [[ZeroConf]].
** Integration with [[K3b]] for burning audio CDs.
** Support for [[KIO|kioslaves]]-based audio CD access. This allows CDs to be ripped to MP3 or Ogg Vorbis using Amarok's file browser or [[Konqueror]].

[[Image:Amarok.png|thumb|right|Amarok 1.4.3 and Wikipedia article functionality]]

==Easter Egg==
Playing a song with the [[Tag (metadata) | tag]] "title" as "Amarok" and "artist" as "Mike Oldfield" produces the following [[On-screen display | OSD]] popup:
<blockquote>
"One of [[Mike Oldfield]]'s best pieces of work, [[Amarok (album) | Amarok]], inspired the name behind the audio-player you are currently using. Thanks for choosing Amarok! Mark Kretschmann Max Howell Chris Muehlhaeuser The many other people who have helped make Amarok what it is"
</blockquote>

==See also==
{{portalpar|free software}}
*[[Comparison of media players]]
*[[meta:KDE and Wikipedia]]

==External links==
{{commons|Amarok}}
*[http://amarok.kde.org/ Amarok homepage]
*{{musicbrainz wiki|AmaroK|Amarok}}
*[http://amaroklive.com/ Amarok Live! - Amarok-centric LiveCD]
*[http://www.fugitivethought.com/projects/amarokcompile/ Guide to compiling Amarok from source without KDE]
*[http://www.jroller.com/page/nwinkler?entry=amarok_and_the_airport_express How-to: Streaming to the Airport Express under Linux] - Description on how to stream audio to Apple's [[AirPort|AirPort Express]] with Amarok under Linux

{{KDE}}

[[Category:Free audio software]]
[[Category:iPod software]]
[[Category:KDE]]
[[Category:KDE Extragear]]
[[Category:Linux media players]]
[[Category:Online music database clients]]
[[Category:Free media players]]
[[Category:MusicBrainz clients]]
[[Category:Podcasting software]]

[[bs:Amarok]]
[[ca:AmaroK]]
[[cs:Amarok (přehrávač)]]
[[de:Amarok (Audio)]]
[[es:Amarok]]
[[fr:Amarok (logiciel)]]
[[gl:Amarok]]
[[hr:Amarok]]
[[it:Amarok]]
[[hu:AmaroK]]
[[nl:Amarok (audiospeler)]]
[[ja:AmaroK]]
[[no:Amarok]]
[[pl:Amarok]]
[[pt:AmaroK]]
[[ru:Amarok]]
[[sl:Amarok]]
[[fi:Amarok (ohjelmisto)]]
[[sv:Amarok]]
[[tr:Amarok (yazılım)]]

User talk:Dicklyon

2007-01-17T21:32:00Z

JSpudeman: Oops..

User talk:Dicklyon

2007-01-17T21:30:38Z

JSpudeman: Opinion, if you please.

File:Refraction reflection as wavelength.png

2007-01-17T21:22:15Z

JSpudeman: Self made image showing an example of refraction and marked for Snell's Law calculations. I release to all '''NON PROFIT CAUSES'''.

== Summary ==
Self made image showing an example of refraction and marked for [[Snell's Law]] calculations. I release to all '''NON PROFIT CAUSES'''.
== Licensing ==
{{self2|GFDL|cc-by-sa-2.5,2.0,1.0}}

User:CManifesto

2007-01-17T19:38:59Z

JSpudeman: Sockpuppeted. Check out the contribs. Definately the same behavior as User:SendInTheClowns and others; contesting Cplot-related actions.

{{sockpuppet|Cplot}}

CEverything as far as I'm concerned!

Wikipedia:WikiProject Optics

2007-01-16T16:48:45Z

JSpudeman: Added a member's section

This is a wikiproject designed for the purpose of expanding, referencing and making more readable, the optics articles within the wikipedia. While optics falls under the scope of [[Wikipedia:WikiProject Physics|Wikiproject Physics]], it's still an extremely expansive topic of great importance.

While optics can be a formula- and algebraically-heavy subject, it's always important to reference things to make sure that they are correct, and to allow us to make the wikipedia on the whole into a more credible source of information than it is. Let's not give those idiots at Encyclopedia Britannica a reason to try and badmouth us by neglecting to reference all of our work thoroughly.

== Active Members ==

{| style="font-size:14px; width: 100%; padding: 10px; border: 2px #000 solid;"
|'''Name'''
|'''Area'''
|'''Comment?'''
|-
|[[User:JCraw]] <nowiki>[Founder?]</nowiki>
|Neuroscientist; presumably optics from physics sub module? [[User:JSpudeman|James S]] 16:48, 16 January 2007 (UTC)
|Founder, according to the history
|-
|[[User:Graphite_Elbow]]
|No idea; add yourself in!
|No idea!
|-
|[[User:JSpudeman]]
| Physics, physical chemistry, chemistry, some/little neuroscience
| Nice to see an optics wikiproject
|}

== Readability ==
The most important thing about an encyclopedia article is that it does not discriminate against fields of endeavour, or against people with different intelligence or knowledge levels. This means that you need to add the information as it is in a book, or in an encyclopedic style, but you also need to make it easy for people to pick up the article and read it from beginning to end.

This doesn't mean that the language has to be "toned" or "dumbed" down, it just means that terms and other things need to be expanded or explained within the sentence to make it clear what the concept is – make the whole article explained within itself, rather than use 5 or 6 concepts a user has to then read fully before being able to understand the article. The concepts don't need to be super-explained, but explained within context. For example:

'''Avoid''':
<div style="border:1px #000 solid; background-color: #EEEEEE; padding:10px;">Refraction is an optical process in which the phase velocity of a particle or ray changes upon the impingement on a border between two media of differing densities.</div>

'''Instead''':
<div style="border:1px #000 solid; background-color: #EEEEEE; padding:10px;">In the field of Optics, refraction is a phenomenon which occurs when a ray or beam of light impinges, or passes through, a border between two materials of different densities causing a change in the wavelength or phase velocity of a particle.</div>

The latter is more readable, mainly because we assume that a user reading the page knows nothing about optics, but has some knowledge of waves and particulate matter.

Now, the golden rule.

<center><h3>Make sure you DEFINE KEY TERMS INITIALLY</h3></center>

It's important to define terms initially, because you must explain the main concepts within that particular part of the topic in order to continue the other paragraphs using the same terms without definitions.

For example:
<div style="border:1px #000 solid; background-color: #DDDDDD; padding:10px;">
=== Some paragraph ===
The wavelength of a photon propagating rectilinearly from a vacuum and impinging upon a border between two refractive media's direction...
</div>

This is all true, but it makes it difficult to pick up on what's going on if you dont know what some terms mean -- in this paragraph, the terms of "rectilinear", "impingement" and "propogation" within this context. So, let's see how we can fix it...

<div style="border:1px #000 solid; background-color: #DDDDDD; padding:10px;">
=== Some paragraph ===
When a photon passes through, or impinges, at 90 degrees parallel to the surface, it is travelling at rectilinear propagation; its angle does not change, and therefore its change....
</div>

== Recap ==
# Don't type paragraphs as if you're trying to teach someone a concept. This includes things like "imagine..." or "think about", or "consider".
# Make sure you explain your terms and conditions before you explain a concept, or explain them within the context of the topic.
# '''Reference all work you add in!'''

__NOTOC__

[[Category:Science WikiProjects]]
[[Category:WikiProject_Physics]]

User talk:Dicklyon

2007-01-16T16:40:06Z

JSpudeman: Oops! Fixed up wikilink

User talk:Dicklyon

2007-01-16T16:39:06Z

JSpudeman: WP optics and infobox things

== DLP ==

In [[DLP#Three-chip_projectors]], you deleted the following text:

<blockquote>Single-chip DLP systems are capable of displaying 16.7 million (24-bit) colors, whereas three-chip DLP systems can display up to 35 trillion (45-bit) colors.</blockquote>

Your edit comment characterized the text that you removed as "silly numerology", once again displaying the gratuitous rudeness that is a frequent feature of your WP participation and is unnecessarily disruptive of collaborative editing.

The explanation that you added is, of course, a worthwhile contribution to the article. However, unless the text that you deleted is inaccurate, it seems to me that the specifics belong in the article in addition to your explanation. Are the deleted data inaccurate? If not, they should be restored. If the data are accurate, I would suggest restoring them after your explanation substantially as follows:

<blockquote>Hence, three-chip DLP systems can display up to 35 trillion (45-bit) colors, whereas single-chip DLP systems are limited to 16.7 million (24-bit) colors.</blockquote>

Further, you really should modify your editing behavior rather than having to apologize so often for it.

[[User:Finell|Finell]] [[User_talk:Finell|(Talk)]] 14:30, 26 October 2006 (UTC)

:I felt that "silly numerology" would be the best way to characterize what was there. I can't help it that you don't like my style, so, per your suggestion, no apology. [[User:Dicklyon|Dicklyon]] 15:03, 26 October 2006 (UTC)

::Please answer: Are the numbers that you removed correct or incorrect? They weren't mine, by the way, so no apology would be due me in any event. Actually, I do like the "style" of the writing you contribute to WP. It is usually a clear and concise expression of worthwhile content. The explanation that you added to [[DLP#Three-chip_projectors]] is a fine example of your very useful contributions. However, I am far from the only Wikipedian who is bothered by your disruptive manner and rude words; others have expressed the same to you. Rudeness is not a "style"; it is anti-social behavior in which you persist. For some time I tried to correct your behavior gently and diplomatically. As that approach failed to improve your behavior, I have become increasingly blunt—a "style" that you ought to understand. [[User:Finell|Finell]] [[User_talk:Finell|(Talk)]] 20:12, 26 October 2006 (UTC)

:::Yes, I get your blunt style. I'm still a bit unsure, though, why a comment about the removed material being "silly numerology" sets you off. It's a fair characterization of the material, and connotes my attitude toward it fairly, and is hence an informative explanation for my edit.

::::Condemning the conscientious (even if sometimes misguided or mistaken) contributions of other editors, who donate their time to WP, as "silly" or "twaddle" is rude and insulting. That is what "sets [me] off", and sets off other editors. You may think that you are merely criticizing text, but in fact you are insulting the human being who wrote it. Frankly, I don't understand why this is not obvious to you, intelligent as you are. When another editor (an admin) called you out for a similarly rude edit summary, you asked if there was some official governing etiquette. I quoted to you from '''[[Help:Edit_summary#Use_of_edit_summaries_in_disputes|WP:ES—Use of edit summaries in disputes]]''', which says, in part, "Avoid using edit summaries ... to express opinions of the other users involved." ''That'' is policy, and it trumps your urge to express your self-perceived superiority over others. Look at the number of criticisms of your behavior, on your own talk page and on the talk pages of articles that you edit. Most active Wikipedians do not draw such criticisms with anywhere near the frequency that you do, and for every criticism that you see, figure that there are 10 more who are equally offended but who lack the courage to confront you. What do you gain by this behavior? More importantly, what does WP gain, and what does it lose, by it? If nothing else, aren't the arguments that you inspire a waste of your time and the time of others? As you see, I have not given up hope of reforming you. I have repeatedly said that you have very worthwhile contributions to make to WP, and I hope you will continue to make them. However, your repeated rudeness, which your own numerous apologies admit, diminishes your usefulness and the willingness of others to accept your edits. [[User:Finell|Finell]] [[User_talk:Finell|(Talk)]] 08:26, 27 October 2006 (UTC)
:::::Finell, I hear your point, but I don't agree that I've operated outside the suggested policy here. "Silly numerology" was an objective comment on the text, not a remark about the person who wrote it. It is a concise way to let that person know that what he wrote may make sense numerologically, but not otherwise. I didn't think I needed to do some politicing on the talk page to document the reason for a simple edit. And there was no argument, either prior to or inspired by my comment, except from you. Now go home. And as for that other admin, one has to wonder who allowed him to become that, increasing his abusive use of power. It you want to see how one recomes involved in raging arguments, even while remaining polite on surface, study his history. Now go away and stop bothering me. [[User:Dicklyon|Dicklyon]] 15:02, 27 October 2006 (UTC)
::::::Dick: I will continue my efforts to socialize your WP behavior when I see behavior that warrants it, but ''not'' otherwise. I am as persistent as you are stubborn. [[User:Finell|Finell]] [[User_talk:Finell|(Talk)]] 16:57, 27 October 2006 (UTC)
:::::::OK, I look forward to your input. Not. [[User:Dicklyon|Dicklyon]] 17:00, 27 October 2006 (UTC)
:::::::Hey, Finell, did you notice the high praise and agreement I got from my nemesis? He said "OK"; the nicest word I've got out of him. Even nicer, he didn't revert my changes now that I've proven that truth and verifiability are not in conflict. [[User:Dicklyon|Dicklyon]] 05:21, 31 October 2006 (UTC)
:::As to whether the numbers are "correct", what do you mean by that? If you mean can one sensibly expect to get 2^(3*15) different colors out of a projector, no, that's just silly numerology. [[User:Dicklyon|Dicklyon]] 23:10, 26 October 2006 (UTC)

Thanks for adding the information on the CBS Color wheel standard. I thought the information was interesting, but it needed a link, so I reverted someone's earlier edit. What you put back helped out a lot! Thank you! --[[User:Mdwyer|Mdwyer]] 17:58, 27 November 2006 (UTC)

==[[Mousepad]] problems==

Hey. I've been keeping an eye on [[Mousepad]] lately, 'cause it seems to be a target for a lot of vandalism, or at least harmful edits. It seems like the same person is doing them, too, overemphasizing stuff and introducing grammatical errors. I noticed you've been working on the article -- or at least getting rid of the semi-vandalism. Would you mind keeping a closer eye on it? It's not that popular an article, and I'm having some trouble dealing with the bad edits, so I wondered if you're interested in helping out/cleaning up. [[User:Switchercat|Switchercat]] [[User_talk:Switchercat|talk]][[Special:Contributions/Switchercat|cont]] 01:47, 1 November 2006 (UTC)

Thanks for fixing the "silicon/e" bits in my reversion, by the way, as I seem to have been a little too brutal with the changes. Good to know that that anon user is correcting some factual errors, at least. [[User:Switchercat|Switchercat]] [[User_talk:Switchercat|talk]][[Special:Contributions/Switchercat|cont]] 01:49, 1 November 2006 (UTC)

:I was thinking of recommending it for deletion. It's obviously written by the inventor himself, trying to stake his claim to fame. It's perhaps a partially fair claim, backed up by the Xerox disclosure journal, but the amount of verbage about him is ridiculous, as is not citing Engelbart who showed a mousepad 10 years earlier. It needs work if it stays. Who has time to take on such a trivial thing, though? I got onto it via some bad stuff he put in the mouse article, which I watch. [[User:Dicklyon|Dicklyon]] 02:48, 1 November 2006 (UTC)
::My dad worked at Xerox around that time, actually, and he's contesting some of the stuff. Says they first used vinyl board cover, not silicone. (And he just looks at what I'm writing and goes, "Dick Lyon! Richard Lyon? Did he work for Xerox too? He did optical mouse." I don't know if you're that guy, but that's kind of interesting.) Mousepads seem notable enough that a vote for deletion wouldn't get rid of it. It ''is'' trivial, yeah; I suspect I'll revert the vandalism and leave it at that for now. Thanks for the input on the disclosure journal, though; I might look into that if I feel like contributing more. [[User:Switchercat|Switchercat]] [[User_talk:Switchercat|talk]][[Special:Contributions/Switchercat|cont]] 03:11, 1 November 2006 (UTC)
:::Yep, that's me. All older now, and wasting my time on wikipedia. Who's your dad? He can mail my handle at acm.org. [[User:Dicklyon|Dicklyon]] 04:26, 1 November 2006 (UTC)

== Gutenberg ==

Very helpful recent edits.including a better wording for my awkward phrase. [[User:DGG|DGG]] 04:27, 14 November 2006 (UTC)
:please check the Village Pump (policy) for an attempt to reopen some related issues.[[User:DGG|DGG]] 05:07, 18 November 2006 (UTC)

== Re: Stop capitalizing ==

Sorry About That - I didn't read that. I have a thing for capitalized titles.
[[User:Christopher Kraus|Christopher Kraus]] 01:22, 16 November 2006 (UTC)
:No problem. I fixed one already, and assume you'll take care of it. Welcome to WP. [[User:Dicklyon|Dicklyon]] 01:25, 16 November 2006 (UTC)

== Supernumeray rainbow image ==

Hi Dicklyon, 
I woud disagree with the replacement as the image I uploaded is of higher res and better quality --[[User:Fir0002|Fir0002]] 05:12, 21 November 2006 (UTC)

:But the green and purple stripes are not as easy to see as in the one you replaced. [[User:Dicklyon|Dicklyon]] 06:18, 21 November 2006 (UTC)

== Gutenberg ==

Thxs for making my talk page stuff clearer. M has moved on to woodcut now, so maybe things will be quieter for you!
[[User:Johnbod|Johnbod]] 20:21, 26 November 2006 (UTC)

== Re:Logarithms.png ==

Looks great! Thanks for letting me know. [[User:Enochlau|enochlau]] ([[User talk:Enochlau|talk]]) 08:56, 27 November 2006 (UTC)

== Old VICAR manuals ==

Sorry but I can't help you with that, I just stumbled on to Billingsley's link with VICAR by coincidence so I added it to the wiki.--[[User:Rxke|Rxke]] 11:02, 29 November 2006 (UTC)

==''West wikipedia'' weirdness==

I demoted all this related stuff from sections to subsections. [[User:Dicklyon|Dicklyon]] 01:26, 18 December 2006 (UTC)

===STOP THE HARASSMENT===
Do NOT delete my external links. The external links that I provide have 100% to do with the article I leave them on. You need to leave my links online as they meet the wikipedia external links policy. —The preceding [[Wikipedia:Sign your posts on talk pages|unsigned]] comment was added by [[User:West wikipedia|West wikipedia]] ([[User talk:West wikipedia|talk]] • [[Special:Contributions/West wikipedia|contribs]]) 05:41, 9 December 2006 (UTC).

:It is customary to answer on the page where the conversation was started. Read the reasons there (on your talk page), instead of deleting them. It is not harassment, just trying to help wikipedia stick to policies. [[User:Dicklyon|Dicklyon]] 05:43, 9 December 2006 (UTC)

===STOP===
I also left this on my user page. You are a spammer and you need to knock it off! Quit deleting relevant external links —The preceding [[Wikipedia:Sign your posts on talk pages|unsigned]] comment was added by [[User:West wikipedia|West wikipedia]] ([[User talk:West wikipedia|talk]] • [[Special:Contributions/West wikipedia|contribs]]) 05:48, 9 December 2006 (UTC).

:I'm amused by your interpretation. [[User:Dicklyon|Dicklyon]] 05:50, 9 December 2006 (UTC)

I also left this on my discussion page - It meets the criteria... You need to stop doing this. If you think this is a violation then why dont you wait and see if any of the other millions of users do

:Not a violation, just not in accord with editorial policies. I'm sure someone else will revert you after I go to bed. [[User:Dicklyon|Dicklyon]] 06:00, 9 December 2006 (UTC)

=== Re: your recent revert to [[Luck]] ===

Hello! Just wanted to ask you about your curious edit [http://en.wikipedia.org/w/index.php?title=Luck&curid=192727&diff=93094615&oldid=92819227 here]. I'm thinking, based on my review of your interaction with [[User:West wikipedia|West wikipedia]], that it may have been an error. I've been doing what I see you do; removing superfluous external links, but your reversion there actually restored them. Heh. Anyway. Just curious. Thanks! -- '''[[User:Weirdoactor|weirdoactor]] [[User talk:Weirdoactor|t]]|[[Special:Contributions/Weirdoactor|c]]''' -- 06:21, 9 December 2006 (UTC)

:Yeah, I goofed on that one by not reading your diff; already reverted myself and apologized. Thanks. [[User:Dicklyon|Dicklyon]] 06:23, 9 December 2006 (UTC)

::No worries! Like I said, it looked like an error, and not malicious. Have a good one! -- '''[[User:Weirdoactor|weirdoactor]] [[User talk:Weirdoactor|t]]|[[Special:Contributions/Weirdoactor|c]]''' -- 06:26, 9 December 2006 (UTC)

=== West wikipedia ===

Is there a reason you reverted and deleted my comment on his talk page? I'm just wondering. - [[User:EronMain|Eron]] [[User Talk:EronMain|Talk]] 17:04, 9 December 2006 (UTC)

:Did I do that wrong? My intention was to restore your comment that he deleted. [[User:Dicklyon|Dicklyon]] 17:17, 9 December 2006 (UTC)

::I'm looking at [http://en.wikipedia.org/w/index.php?title=User_talk%3AWest_wikipedia&diff=93171449&oldid=93168204 this diff]. I think he deleted a comment before mine, and then you reverted to restore that deletion. He hasn't actually edited the page since I commented. No worries, it was an honest mistake. I just wanted to make sure there wasn't a perceived problem with my comment. Thanks. - [[User:EronMain|Eron]] [[User Talk:EronMain|Talk]] 17:22, 9 December 2006 (UTC)

=== Absolute Jerk ===
This is extremely innapporiate and childesh of you to put this kind of material on wikiepdia. "Speaking of external links, this guy User:West wikipedia is spamming lots of pages with his links to his earlyhistory.googlepage.com pages, which are trivialized histories with lots of error, not anything useful. If he puts one back here, someone else deal with him for a while, as I'm getting tired of it. Dicklyon 06:08, 9 December 2006 (UTC)" Because of you and your stupidish child like behavior I am no longer planning on ever using wikipedia. You need to grow up. How old are you? Maybe 11 or 12. Have a good day
West wikipedia {{unsigned|West wikipedia}}

:OK, I will. [[User:Dicklyon|Dicklyon]] 20:20, 9 December 2006 (UTC)

==Climate change==

Thank you for cleaning up my text on 'Climate change' The only reason that I intruded into the
article was to correct one statement about all the energy in the earths climate system coming from the sun. Energy and heat are not the same, the energy needed to keep the atmosphere in place on the surface of the earth comes from gravity, while the energy used to move warm air from the equator to the poles is the spinning of the earth. The source of the heat comes from the sun and I would imagine its close to 99.9 percent. While friction might contribute some heat and geothermal some, its very small. Note if you go into caves or mines most any were in the world the tempeture. is lower than the yearly average of the surface for that location ( the same for the bottom of the oceans) - so geothermal does not contribute much if any surface warming. Thank you for your time. [[User:Hardyplants|Hardyplants]] 11:27, 14 December 2006 (UTC)

:You're welcome, but I think you're very confused about what energy is. I just fixed the grammar. [[User:Dicklyon|Dicklyon]] 16:44, 14 December 2006 (UTC)

== "Dither" dictionary images ==

Hello! Thanks very much for uploading the images of old dictionary definitions; I found them extremely interesting. However, I did remove them from the article [[Dither]], because they really aren't relevant to image dithering, no matter how interesting they are on their own.

Have you looked into [[Wiktionary]]'s policy on images? I've never seen an image on Wiktionary, but if they ''are'' image-friendly, that would be the perfect place for those images. [[Dither]] already links to [[wikt:dither]], so they'd be almost as accessible from there. --[[User:Quuxplusone|Quuxplusone]] 19:15, 14 December 2006 (UTC)

:I thought the images supported the "origin of the word" section pretty well, by showing that the meaning was long established and just got adapted to this technical use. It's often hard to find good PD images for articles, which look so drab as just text. I might put them back... why don't you bring up the question of relevant on the talk page and see how others feel? [[User:Dicklyon|Dicklyon]] 19:23, 14 December 2006 (UTC)

==Ludvikus's octothorp tirades==

I demoted all these sections to subsections. [[User:Dicklyon|Dicklyon]] 01:23, 18 December 2006 (UTC)

=== [[Octothorp]] ===
I object your suppression of the above term without discussion on the discussion page.
:You could, if you wish, comment on its use,or lack thereof, but you cannot ignore the fact that it is the name for the "number sign" according to [[Merriam-Webster's]]!!!
::[[Yours truly,]]--[[User:Ludvikus|Ludvikus]] 04:47, 17 December 2006 (UTC)
:Don't worry, it is not being ignored. In fact it was I who added most of the content of the octocthorp section, including the mention of the Merriam-Wester Book of Word Histories 1991 article. You should read that one. Maybe I'll add a quote from it. I also am in contact with two of the guys that have written up their claims for having originated the term when at AT&T: Doug Kerr and Lauren Asplund; I need to write up a bit about the latter now that he has sent me his evidence, which doesn't actually say much. [[User:Dicklyon|Dicklyon]] 06:18, 17 December 2006 (UTC)
:By the way, the first google hit for octothorpe, at World Wide Words, say "This word is beginning to appear in a few dictionaries, but still seems mostly to be a jargon term of the North American telephone business. It has reached semi-official status by being mentioned in international standards documents but that’s no guarantee of a wide circulation any time soon." This is about how it should be represented in the article, not as an accepted or widely used term. [[User:Dicklyon|Dicklyon]] 06:22, 17 December 2006 (UTC)

=== Octothorpe ===
Google hits: 74,200 [http://www.google.com/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=Octothorpe&spell=1]
:[[Yours truly,]]--[[User:Ludvikus|Ludvikus]] 04:58, 17 December 2006 (UTC)
::And number-sign and pound-sign each have over a half million. So what? [[User:Dicklyon|Dicklyon]] 06:12, 17 December 2006 (UTC)

===Octothorp 2===
''It seems people are unaware that this term had entered the language in [[1971]]:'' '''octothorp \ak-te-thorp, -to-\ noun [octo- + thorp, of unknown origin; fr. the eight points on its circumference] (1971)'''
:'''the symbol #'''
:'''C) 1996 Zane Publishing, Inc. and Merriam-Webster, Incorporated'''
::[[Yours truly,]]--[[User:Ludvikus|Ludvikus]] 04:57, 17 December 2006 (UTC)
:Why do you think we are unaware? Read what the article says. Octothorp remains an obscure and unofficial name for the number sign, and we should not be elevating it the way you have. I have reverted your changes. Anyone object? [[User:Dicklyon|Dicklyon]] 15:46, 12 December 2006 (UTC)

::Google hits for [[Octothorp]]: 24,800 [http://www.google.com/search?hl=en&q=Octothorp&btnG=Google+Search]
:[[Yours truly,]]--[[User:Ludvikus|Ludvikus]] 04:57, 17 December 2006 (UTC)

=== [[Unicode]] vs. [[Typewriter]] & [[Telephone]] ===

*[[Unicode]] is a relatively recent technical usage.

*The [[Typewriter]] has been arround since the 19th century - and though I have not, every typewriter I have used or come accross had this [[octothorp]] or [[number sign]] on its ASCII type set.

*Similarly, since the 12-botton phone key-pad has been arround (I don't recall the situation regarding the rotary phone), the symbol, "'''#'''", has been arround. So it is not what the [[Unicode]] community legislates that is to be prioritized. Rather, it is the common users of the typewriter and telephone who give us the meaning of this sign or symbol. --[[User:Ludvikus|Ludvikus]] 20:15, 17 December 2006 (UTC)

::The term ''octothorp'' comes from the telephone guys after they developed the 12-key pad, as extensively documented in the article and its referenced and linked sources. Do you have anything to add? [[User:Dicklyon|Dicklyon]] 01:23, 18 December 2006 (UTC)

=== [[ASCII]] ===
[[Image:Ascii full.png|right]]

In other words, I'm talking about the 32 [[ASCII]] charaters!
:And I'm asking you, '''what is the 3rd character called?'''
:Are you going to omit--AT THE TOP PARAGRAPH--the uncommon name [[octothorp]]? Why? Because of [[Unicode]] conventions? I did not find that convention in Merriam-Webster when I looked up the term!
::What's the third sign/symbol called, besides "number sign"? Here's a picture for you:

:::[[Yours truly,]] [[User:Ludvikus|Ludvikus]] 20:39, 17 December 2006 (UTC)

::::Everything I can find about ASCII calls it "number sign"; see for example [http://www.columbia.edu/kermit/ascii.html this table] which might be from the standard (not sure). Its other names are all discussed at length in the [[number sign]] article. Please add to it if anything was missed. Octothorp was not missed. [[User:Dicklyon|Dicklyon]] 01:23, 18 December 2006 (UTC)

=== [[Number sign]] & 1994-1996 [[Merriam-Webster's]] ===
*By the way, there's no entry for "[[number sign]]" in said MW!!!
:So much the worse for "number sign," but better ''for my beloved'' "octothorp"!!! [[User:Ludvikus|Ludvikus]] 20:44, 17 December 2006 (UTC)
[[Yours truly,]]--[[User:Ludvikus|Ludvikus]] 20:49, 17 December 2006 (UTC)

:Your emotional attachment to an obscure name for a character that has a standard name is hardly encyclopedic. Get over it. [[User:Dicklyon|Dicklyon]] 01:23, 18 December 2006 (UTC)

==Your edit to [[:Johannes Gutenberg]]==
Your recent edit to [[:Johannes Gutenberg]] ([http://en.wikipedia.org/w/index.php?title=Johannes_Gutenberg&diff=95015526&oldid=95010430 diff]) was reverted by an '''automated bot''' that attempts to recognize and repair [[Wikipedia:vandalism|vandalism]] to Wikipedia articles. If the bot reverted a legitimate edit, please accept my humble creator's apologies – if you bring it to the attention of the bot's owner, we may be able to improve its behavior. '''[[User:AntiVandalBot/FAQ|Click here]]''' for '''frequently asked questions''' about the bot and this warning. // [[User:AntiVandalBot|AntiVandalBot]] 14:05, 18 December 2006 (UTC)

== [[Philosophy]]==
Dear [[User:Dicklyon]],
*We first have encountered one another over the article on the [[Number sign]].
**You might perhaps recall that I was rather partial to the more poetic, [[Orobouros]]?
***I - civily I might add - differred to your, probably much more studied position.
*Subsequently, we met over [[Book design]] vs. the much newer article, [[Book elements]]. That, I think you'll agree, is currently in a state of flux.
*Be that as it may, I write to you in the hope that I might get your assistance in an area of my special expertise, which [[Philosophy]].
**I've encountered a particularly subborn user, and I thought that, possibly, you might be of assistance in resolving the conflict!
***Will you please visit the article and see if you could contribute a ressolution?
****I do not wish to engage in the game of--what I call--ping-pong REVERSIONS!!!
:[[Yours truly,]] [[User:Ludvikus|Ludvikus]] 18:43, 28 December 2006 (UTC)
Ludvikus, perhaps I should be flattered that you think I can be more stubborn than your current nemesis. However, I'm no expert in philosophy, and after quick look I don't see how to contribute to the argument that seems to be primarily over the scope of the article. You might consider proposal separate articles on eastern and western philosophies, and make the main article simply a dispath page for those. Take it to the talk page and see if you can get some consensus. When it's just two editors arguing, it's unlikely to resolve. [[User:Dicklyon|Dicklyon]] 21:37, 28 December 2006 (UTC)

== Snell's Law ==

Sorry, i should have explained my comment further. It's strange, but the amount of books which include snell's law usually just expand onto wavelength and phase velocity when it's nothing to do with snell's law, implicitly. Well, good work on the change, anyway - i bought [[User:JCraw]] an optics book this x-mas for him to devour.

Still, snell's law in it's normal sense is expressed as <math>_1n_2 = \frac{\sin \theta_1}{\sin \theta_2}</math>, isn't it? In that case, the wavelengths and other things, providing they are expressed in the same units would result in a the refractive index anyway, wouldn't they? After all, the angle of refraction is expressed through the use of the refractive indecies isn't it? Well, it's been a while since i did physics.. it was 10 years ago when i did it in university :-/ [[User:JSpudeman|James S]] 20:15, 28 December 2006 (UTC)

:Your equation is a bit malformed, but I suppose you mean a form that is solved for an index of refraction. It's true that you an also express that index in terms of wavelengths or velocities. But that's not Snell's law, which is the law about the angles. [[User:Dicklyon|Dicklyon]] 21:39, 28 December 2006 (UTC)

::That equation seems fine.. i've seen it wrote that way many times, just as shorthand for the second refractive index. [[Image:SConfident.gif|15px]] [[User:JCraw|J O R D A N]] <nowiki>[</nowiki>[[User talk:JCraw|talk]] <nowiki>]</nowiki> 12:41, 2 January 2007 (UTC)

::The equation starts with a subscript 1 and has no n1 in it; if that's intentional, please explain. [[User:Dicklyon|Dicklyon]] 18:46, 2 January 2007 (UTC)

== Electronic circuit ==

Thanks for your help on the circuits pages. I did not realize it was a violation of protocol to move text from one page to another. Next time, I'll check the policies first. In the meantime, can you delete [[Electral circuit]]? I think there are some redirects on the talk pages which put everything on the talk page for Electral circuit, so those should be changed first.

:You're welcome. Moving material is not a violation, but moving whole pages is. You may have been over the border. Use the move link next time. I'll add a "prod" to the electral page. [[User:Dicklyon|Dicklyon]] 08:10, 2 January 2007 (UTC)

By the way, can you deal with the apparent contradiction between [[Active device]] and [[Active component]]? It seems there are two different usages for these terms:

1. transistors, vacuum tubes, etc.
2. power sources

It would be convenient if there were a 1:1 relationship between scientific concepts and the terms that refer to them, but we don't live in that world. I think an information source such as Wikipedia should clarify ambiguities by defining all usages, not arbitrarily selecting one and pretending that there is no other usage. Since you are an engineer, you are probably much more familiar with the literature than I am. I'd rather ask someone like you to do it than leave a <nowiki>{{Contradict-other|[[Article]]}}</nowiki>

--[[User:Cbdorsett|Cbdorsett]] 07:33, 2 January 2007 (UTC)

:Yeah, it's not so clean. "Active" is used for the things that produce electrical energy as well as for things that can be used to get some gain or oscillation in a circuit. And what about a diode? Is that active? Depends on your source; see [http://books.google.com/books?as_q=diode&num=10&btnG=Google+Search&as_epq=active-devices&as_oq=&as_eq=&as_libcat=0&as_brr=0&as_vt=&as_auth=&as_pub=&as_drrb=c&as_miny=&as_maxy=&as_isbn= GBS]. I think the different definitions need to be sourced and compared, and depending on how it looks maybe those articles should be merged. But one is more electronic and the other more general, so probably not. [[User:Dicklyon|Dicklyon]] 08:10, 2 January 2007 (UTC)

== Revert to [[Snell's Law]] ==

Care to explain? Just curious is all.. the introduction there was referenced in the previous version.. Not pointing fingers or being nasty, i'm just generally curious. [[User:JSpudeman|James S]] 19:14, 4 January 2007 (UTC)
:I have to say, i'm happy to see another wikipedian who actually posts comments on talk pages -- you have my appreciation. I'll add in the references, and generally clean up the introduction so it's grammatically correct. I've bought myself an optics book and it too says that Snell's law is, indeed, the full formula specified further down the page on the article. I've checked it out in several physics books i've got and they generally resolve it the same.

:I've not found a book yet which lists the actual formula as it was specified by Willebrord Snellius or other contrbutors. Generally, though, they do agree that it's defined as the relationship between the angle of refraction and the refractive indeces of two materials, and is generally re-arranged to find incident/refractive angles. Still, how true this is based upon the original formula(e) is unknown to me. Cheers, [[User:JSpudeman|James S]] 19:31, 4 January 2007 (UTC).

::Let's take it back to [[Talk:Snell's law]]. [[User:Dicklyon|Dicklyon]] 22:14, 4 January 2007 (UTC)

== Question ==

Hello. I know that you have a lot of experience with Wikipedia so I would like to come to you with a question. I was looking at the [[Deere & Company]] page and in the external links there is a link to http://www.tractordata.com/td/johndeere.html - According to the guidelines for external links people should only place official links and that is not official. Would I be right in taking that link off? I don't want to do it if you think that would not be appropriate. As you know I used to add things to Wikipedia that would make me be considered as a [[Vandal]], however, I would like you to know that I am not at all like that anymore. If you don't mind I would like to come to you with my questions and hope that we will be able to get along! Thanks [[User:Eric outdoors|Eric]] 02:43, 5 January 2007 (UTC)

:The critera are not so strict, usually. See [[WP:EL]]. If in doubt, mention it on the article's talk page and seek the advice of more experienced editors of that article. It looks to me like probably the work of guy who makes lots of info site to try to get some advertising revenue, but I'm not sure. [[User:Dicklyon|Dicklyon]] 03:00, 5 January 2007 (UTC)

::I looked at the history of the page and there is not really anyone that really makes a lot of consistent edits on the page. The page is really about the John Deere Company NOT John Deere tractors so i think that link does not belong there. What should I do in a situation which there are no consistent editors to ask. Should I just go ahead and remove the link? Thanks for your time [[User:Eric outdoors|Eric]] 03:11, 5 January 2007 (UTC)

:::Click on "discussion". Add a new section at the bottom to say what you're intending to do, and see if anyone objects; you don't need to address anyone in particular. Or, if you're confident enough, just be bold and do it, and see if anyone objects. [[User:Dicklyon|Dicklyon]] 03:16, 5 January 2007 (UTC)

::::Thank You!

==Read it and weep==
Observe:

They are used to denote possession, for example:
the dog's bone
the company's logo
Jones's bakery (but Joneses' bakery if owned by more than one Jones)

... but please note that the possessive form of it does not take an apostrophe any more than ours, yours or hers do

the bone is in its mouth

... however, if there are two or more dogs, companies or Joneses in our example, the apostrophe comes after the 's':
the dogs' bones
the companies' logos
Joneses' bakeries {[http://www.apostrophe.fsnet.co.uk/ Source])

As you can plainly see, I am '''''NOT''''' making this up. [[User:TomStar81|TomStar81]] ([[User talk:TomStar81|Talk]]) 01:31, 7 January 2007 (UTC)

:But we were not talking about multiple [[Fort Bliss]]es, just one. See [[Apostrophe#Singulars]]. [[User:Dicklyon|Dicklyon]] 01:52, 7 January 2007 (UTC)

:Yeah, I see that now. This was more of a "yes, there is such a thing as an apostraphe with no s" than an "I'm right and your wrong, so shove it" kind of thing. Ordinarilly I do not argue with, or revert, gramatical changes (or spelling changes, for that matter) in articles that I create, wrote, or moniter becuase I know that my grammar and spelling suck. In this one case though, I remembered hereing something about not adding apostrophes after the letter s if the word being apostrosized ended in an s, although it does appear that I am, in fact, in the wrong. Sorry if I offended you, as that was not my intention, and thank you for catching the mistake. [[User:TomStar81|TomStar81]] ([[User talk:TomStar81|Talk]]) 02:46, 7 January 2007 (UTC)

::No offense taken. Glad I could teach you something. [[User:Dicklyon|Dicklyon]] 05:09, 7 January 2007 (UTC)

== Popups ==

You might want to be careful what you use the reverting feature of popups for. You appear to be using it to revert good faith edits sometimes, and if done at the wrong time that can make things a bit messy. --[[User:Deskana|Deskana]] [[User talk:Deskana|(For Great Justice!)]] 18:19, 7 January 2007 (UTC)

:Can you provide an example? [[User:Dicklyon|Dicklyon]] 18:22, 7 January 2007 (UTC)

::[http://en.wikipedia.org/w/index.php?title=Golden_rectangle&diff=prev&oldid=99128539 This]. [http://en.wikipedia.org/w/index.php?title=George_W._Bush&diff=prev&oldid=99134496 And this]. It wasn't vandalism, seems like a good faith edit. Doesn't mean it didn't need reverting. It's similar to the reasons that administrators aren't supposed to use the rollback function when reverting good faith edits. --[[User:Deskana|Deskana]] [[User talk:Deskana|(For Great Justice!)]] 18:25, 7 January 2007 (UTC)

:::OK, got it. I'll use undo and a comment next time. [[User:Dicklyon|Dicklyon]] 18:55, 7 January 2007 (UTC)

::::Thanks. :-) --[[User:Deskana|Deskana]] [[User talk:Deskana|(For Great Justice!)]] 20:11, 7 January 2007 (UTC)

==[[Rolf Rodenstock]]==
I have added a "{{[[Template:prod|prod]]}}" template to the article [[Rolf Rodenstock]], suggesting that it be deleted according to the [[Wikipedia:Proposed deletion|proposed deletion]] process. All contributions are appreciated, but I don't believe it satisfies Wikipedia's criteria for inclusion, and I've explained why in the deletion notice (see also "[[Wikipedia:What Wikipedia is not|What Wikipedia is not]]" and [[Wikipedia:Deletion policy|Wikipedia's deletion policy]]). Please either work to improve the article if the topic is worthy of inclusion in Wikipedia, or, if you disagree with the notice, discuss the issues at [[Talk:Rolf Rodenstock|its talk page]]. Removing the deletion notice will prevent deletion through the proposed deletion process, but the article may still be sent to [[Wikipedia:Articles for deletion|Articles for Deletion]], where it may be deleted if consensus to delete is reached, or if it matches any of the [[Wikipedia:Criteria for speedy deletion|speedy deletion criteria]]. [[User:172.144.122.155|172.144.122.155]] 04:41, 9 January 2007 (UTC)

== Overexposure / Golden Hour Photography ==

Thanks for rewriting this - you did a much better job than I did. Good writing and fluid language are important, I enjoy them, but I can't produce it. The article reads a lot better now. [[User:ForrestCroce|ForrestCroce]] 07:48, 9 January 2007 (UTC)
==License tagging for Image:CheatSheetEV.png==
Thanks for uploading [[:Image:CheatSheetEV.png]]. Wikipedia gets thousands of images uploaded every day, and in order to verify that the images can be legally used on Wikipedia, the source and copyright status must be indicated. Images need to have an [[Wikipedia:Image copyright tags|image tag]] applied to the [[Wikipedia:Image description page|image description page]] indicating the copyright status of the image. This uniform and easy-to-understand method of indicating the license status allows potential re-users of the images to know what they are allowed to do with the images.

For more information on using images, see the following pages:
* [[Wikipedia:Image use policy]]
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This is an automated notice by [[User:OrphanBot|OrphanBot]]. If you need help on selecting a tag to use, or in adding the tag to the image description, feel free to post a message at [[Wikipedia:Media copyright questions]]. 08:07, 10 January 2007 (UTC)

== Transistor images ==

Hi, i have changed the transistor image on the page [[transistor]] back to the newly photographed version. The old is too shiny and 3 of 6 shapes are almost never used. (And I do not consider the red background to be nice.) I think it is useful to let the reader see how ''real'' transistor looks and what size it has. It is a bit frustrating, that the change was reverted without plausible reason... --[[User:FDominec|FDominec]] 15:51, 12 January 2007 (UTC)

: And I am going to make new (more contrast and simplier) version of this
image.--[[User:FDominec|FDominec]] 21:45, 12 January 2007 (UTC)
== Rodenstock==
There are quite a number of people prodding and even speedying technical articles which they do not understand. It's hard to catch them, and I've been commenting on the speedy talk page.'''[[User:DGG|DGG]]''' 05:32, 14 January 2007 (UTC)

:Oh, well, part of the game. I just prodded one myself: [[Hendy's Law]]. [[User:Dicklyon|Dicklyon]] 05:42, 14 January 2007 (UTC)

== No personal attacks ==

{{{{{subst|}}}#if:Talk:Standard test image|With regards to your comments on [[:Talk:Standard test image]]: }}Please see Wikipedia's [[Wikipedia:No personal attacks|no personal attacks]] policy. Comment on ''content'', not on contributors; personal attacks damage the community and deter users. Note that continued personal attacks may lead to [[Wikipedia:Blocking policy|blocks]] for disruption. Please [[Wikipedia:Staying cool when the editing gets hot|stay cool]] and keep this in mind while editing. Thank you.  --[[User:Oden|Oden]] 02:51, 15 January 2007 (UTC)

:With regard to [http://en.wikipedia.org/w/index.php?title=Talk:Standard_test_image&curid=3847006&diff=100787752&oldid=100779363 this diff]. --[[User:Oden|Oden]] 02:51, 15 January 2007 (UTC)

::OK; I'll edit my comment to a cooler version. [[User:Dicklyon|Dicklyon]] 02:53, 15 January 2007 (UTC)

== large blocks of quoted text ==

Hello, and [[Wikipedia:Welcome, newcomers|welcome to Wikipedia]]. We appreciate your {{#if:Lenna|contributions to the [[:Lenna]] article|contributions}}, but for legal reasons, we cannot accept [[Wikipedia:Copyrights|copyrighted]] text or images borrowed from other web sites or printed material, and as a consequence, your addition will most likely be deleted.

Feel free to re-submit a new version of the article. You may use external websites as a source of ''information'', but not as a source of ''sentences''. This part is crucial: ''say it in your own words''.

If the external website belongs to you, and you want to allow Wikipedia to use the text — which means allowing other people to modify it — then you must include ''on the external site'' the statement "I, (name), am the author of this article, (article name), and I release its content under the terms of the [http://www.gnu.org/copyleft/fdl.html GNU Free Documentation License], Version 1.2 and later."

You might want to look at [[Wikipedia:Policies and guidelines|Wikipedia's policies and guidelines]] for more details, or ask a question [[Wikipedia:Village pump (assistance)|here]]. You can also leave a message on my talk page. --[[User:Oden|Oden]] 08:01, 15 January 2007 (UTC)

:What template did you subst that from? I don't find anything about "quote" on the referenced pages. The paragraphs I quoted are certainly not large blocks of text, and the largest is from a magazine, not a web page. As I pointed out in the talk page there, it makes little sense to try to paraphrase a second-hand story of a recollection and try to pass it off as verifiable information; much better to just quote the story and attribute the source; it's not a big part of the referenced publication, just a bit for historical commentary. [[User:Dicklyon|Dicklyon]] 08:06, 15 January 2007 (UTC)

::I have sent the matter to [[Wikipedia:Administrators' noticeboard/Incidents]] ([Wikipedia:Administrators%27_noticeboard/Incidents#Lenna_and_quotes here]) since the article is in violation of our [[WP:FUC|fair use policy]]. --[[User:Oden|Oden]] 08:24, 15 January 2007 (UTC)

:::Thanks. I will respect their opinion on this. [[User:Dicklyon|Dicklyon]] 08:26, 15 January 2007 (UTC)

== Difference between "what he said" and "what is easier to understand" ==

Just wanted to address a little point, which nags me a little, but i'm just addressing it. The main difference is that i agree with you all points when you're talking about referencing almost "to the letter" of what a particular physicist/mathematician said.. particularly because it gives a greater understanding of the topic, amongst other things.

Then again, i remind myself that it's the Wikipedia, and not everything that physicists say is very easy to understand by other non-physicists, because we're not poets or writers, but physicists. Sometimes it's easier to take on board what a physicist wrote, and expand upon it so it makes more sense to others reading the article for the first time than just write a half-coherent sentence that is 100% compliant.

Not to do with the S/L article, just a little bit of advice, perhaps. [[User:JSpudeman|James S]] 20:22, 15 January 2007 (UTC)

:Sorry, I've editted a few hundred articles in the last day, and I don't know what article you mean to refer to by S/L or what exactly you're talking about. Care to get specific? [[User:Dicklyon|Dicklyon]] 20:58, 15 January 2007 (UTC)

:Oh, I see from your contribs that you mean [[Snell's law]]. I still don't get your point, though. Can you refer to an edit or a quote or whatever? [[User:Dicklyon|Dicklyon]] 21:02, 15 January 2007 (UTC)

::Apologies. What i'm saying is, even though a text by Decartes, Huygens, or any other optician may describe snell's law in a definite way, it might not be ideal to include it in the wikipedia article exactly as it is stated, because there's a different audience being addressed. On one hand, Huygens or Descartes would be publishing work specifically for it to be read by physicists in the majority, whereas the wikipedia aims to allow anyone to read it.

:In other words -- we should allow anyone who reads the article to understand it, physicist, poet, or otherwise. Sorry if my responses are somewhat cryptic, I'm not really a person who likes to post on the wikipedia talk pages, or generally reply on forums or internet-based chatter. [[User:JSpudeman|James S]]
::Well, if you want to make a point you do need to speak up. I've just re-editted your changes to the article to make it more correct. I agree it needs to be accessible in modern terms, which is why I'm not quoting the original Latin and French. But it also needs to not be perverted to where what the law is is lost. See if you like what I've done, even if perhaps it doesn't necessarily make Snell's law accessible to the average poet. [[User:Dicklyon|Dicklyon]] 21:42, 15 January 2007 (UTC)
:::Well, technically, i dont have a "voice" on the wikipedia until i make a spoken version of the article :-P. But yes, the edits are good. Similarly, i'd like to think you're not adding the original latin or french because this is the english wikipedia.
:::Also, yes. No perversion is good perversion. [[User:JSpudeman|James S]] 21:59, 15 January 2007 (UTC)
::::How poetic. [[User:Dicklyon|Dicklyon]] 22:04, 15 January 2007 (UTC)

Come off it. [[User:JSpudeman|James S]] 22:21, 15 January 2007 (UTC)

{| style="text-align:center; font-size:14px;" align="right"
|[[Image:Dicklyon.jpg|150px]]
Shakespeare
|[[Image:Shakespeare.jpg|165px]]
Dick Lyon
|}
:Yes, the resemblance is striking. Swapped at birth. [[User:Dicklyon|Dicklyon]] 23:06, 15 January 2007 (UTC)

== Infoboxes for optics articles ==

Do you think it'd be a good idea to have an infobox for optics, which contains formulae info, etc? —The preceding [[Wikipedia:Sign your posts on talk pages|unsigned]] comment was added by [[User:JSpudeman|JSpudeman]] ([[User talk:JSpudeman|talk]] • [[Special:Contributions/JSpudeman|contribs]]) 14:15, 16 January 2007 (UTC).

:I don't know. I'm not a big fan of infoboxes. They tend to be sort of limiting, hard to improve or extend. What do you have in mind exactly? [[User:Dicklyon|Dicklyon]] 16:07, 16 January 2007 (UTC)

::Well, i'm not too sure how it'd look, but it could be something small that lists related concepts in optics. I'm with you though, i'm not that big a fan of them if they don't look too good, but i think a nice little infobox could make it easier to browse around optics articles. Also.. i found out there's [[Wikipedia:Wikiproject Optics]].. interested in joining? [[User:JSpudeman|James S]] 16:39, 16 January 2007 (UTC)

User talk:Dicklyon

2007-01-16T14:15:12Z

JSpudeman: Infoboxes for optics articles

User:JSpudeman

2007-01-16T00:12:46Z

JSpudeman:

<div style="position:absolute; z-index:100; right:10px; top:10px;" class="metadata">[[Image:Pinguim Crystal 2000.png|30px]]</div>
==== I will currently be focusing my Wikipedia-related efforts to OpenMRS to further humanity. See you on the other side ====
{{User:J.Spudeman}}

User talk:Dicklyon

2007-01-15T22:21:55Z

JSpudeman:

User talk:Dicklyon

2007-01-15T21:59:55Z

JSpudeman: Meep Meep.

User talk:Dicklyon

2007-01-15T21:38:29Z

JSpudeman: If you're available on IRC or KDEtalk, i'd prefer that. We could resolve a positive direction for the Snell's Law article a lot quicker than punctuated chats on wikipedia.

User talk:Dicklyon

2007-01-15T20:22:39Z

JSpudeman: Difference between "what he said" and "what is easier to understand"

Snell's law

2007-01-15T20:12:28Z

JSpudeman: Oops

[[Image:Snells law.svg|thumb|300px|[[Refraction]] of light at the interface between two media of different [[refractive index|refractive indices]], with n2 > n1. Since the velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.]]

In [[optics]] and [[physics]], '''Snell's law''' (also known as '''Descartes' Law''' or the '''law of refraction'''), is a [[mathematical formula|formula]], which used to describe the relationship between the [[sine]]s of angles of incidence and refraction as constant, when referring to light or other [[wave]], passing through a boundary between two or more different [[isotropic]] [[medium (optics)|media]], such as air or glass. In it's modern forms, the law can be manipulated to identify the angles of [[angle of incidence|incidence]] or [[angle of refraction|refraction]], and can be further used to identify the [[refractive index]] of a material.

Named for one of it's discoverers, [[Willebrord Snellius]], Snell's law follows from [[Pierre de Fermat]]'s [[Fermat's principle|principle of least time]], which states that the ratio of the [[sine]]s of the angles of incidence and refraction is equal to the ratio of [[velocities]] in the two media, or equivalently the inverse ratio of the indices of refraction:

{| cellspacing="10"
|<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{n_2}{n_1}</math>
| or
|<math>n_1\sin\theta_1 = n_2\sin\theta_2</math>
|}
== History ==
[[Image:Snell Law of Sines 1837.png|thumb|right|300px|An 1837 view of the history of "the Law of the Sines"<ref>William Whewell, ''History of the Inductive Science from the Earliest to the Present Times'', London: John H. Parker, 1837.</ref>]]
Snell's law was first discovered and described by [[Ibn Sahl]] in a manuscript written c.[[984]],<ref>{{cite journal | author=Rashed, Roshdi | title= A pioneer in anaclastics: Ibn Sahl on burning mirrors and lenses | journal= [[Isis (journal)|Isis]]| year= 1990| volume= 81| pages= 464–491 |doi=10.1086/355456}}</ref> who used it to work out the shapes of lenses that focus light with no geometric aberrations, known as [[anaclastic lens]]es. It was discovered again by [[Thomas Harriot]] in [[1602]],<ref>{{cite journal | author=Kwan, A., Dudley, J., and Lantz, E. | title=Who really discovered Snell's law? | journal=[[Physics World]] | year=2002 | volume=15 | issue=4 | pages=64 |url=http://physicsworldarchive.iop.org/index.cfm?action=summary&doc=15%2F4%2Fphwv15i4a44%40pwa-xml&qt=}}</ref> who did not publish his work.

In [[1621]], it was discovered yet again by Willebrord Snel, in a mathematically equivalent form, but unpublished during his lifetime. [[René Descartes]] independently derived the law using heuristic momentum conservation arguments in terms of sines in his [[1637]] treatise ''[[Discourse on Method]]'' (though detractors such as Fermat accused Descartes of working toward the already known answer with sophistic reasoning), and used it to solve a range of optical problems. Rejecting Descartes' solution, Pierre de Fermat arrived at the same solution based solely on his principal of least time.

In [[French language|French]], Snell's Law is called "la loi de Descartes" or "loi de Snell-Descartes."

== Explanation ==
Snell's law is used to determine the direction of light rays though refractive media with varying indices of refraction. The indices of refraction of the media, labeled <math>n_1,n_2</math> and so on, are used to represent the factor by which light is "slowed down" within a refractive medium, such as glass or water, compared to its velocity in a vacuum.

As light passes the border between media, depending upon the relative refractive indices of the two media, the light will either be refracted to a lesser angle, or a greater one. These angles are measured with respect to the ''normal line'', the perpendicular to the boundary. In the case of light traveling from air into water, light would be refrated towards the normal line, due to the fact that the light is slowed down in water; light traveling from water to air would refract away from the normal line.

Refraction between two surfaces is also referred to as ''reversible'' due to the fact that if all conditions were identical, the angles would be the same for light propagating in the opposite direction.

Snell's law is only generally true for isotropic media (such as [[glass]]). In [[anisotropic]] media such as some [[crystal]]s, [[birefringence]] may split the refracted ray into two rays, the ''ordinary'' or ''o''-ray which follows Snell's law, and the other ''extraordinary'' or ''e''-ray which may not be co-planar with the incident ray.

When the light or other wave involved is monochromatic, that is, of a single frequency, Snell's law can also be expressed in terms of a ratio of wavelengths in the two media, λ1 and λ2:

:<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{\lambda_1}{\lambda_2}</math>

=== Total internal reflection ===
[[Image:Refraction internal reflection diagram.PNG|thumb|220px|right|An example of the angles involved within total internal reflection.]]
When light moves from a dense to a less dense medium, such as from water to air, Snell's law cannot be used to calculate the refracted angle when the resolved sine value is higher than 1. At this point, light is reflected in the incident medium, known as internal reflection. Before the ray totally internally reflects, the light refracts at the '''critical angle'''; it travels directly along the surface between the two refractive media, without a change in phases like in other forms of optical phenomena.

As an example, a ray of light is incident at <math>50^o</math> towards a water–air boundary. If the angle is calculated using Snell's Law, then the resulting sine value will not invert, and thus the refracted angle cannot be calculated:

:<math>\theta_2 = \sin^{-1} (\frac{n_1}{n_2}\sin\theta_1) = \sin^{-1} (\frac{1.333}{1.000}0.766) = \sin^{-1} 1.021</math>

Snell's Law cannot calculate such angles because there is no refracted outgoing ray.

In order to calculate the critical angle, let <math>\theta_2 = 90^o</math> and solve for <math>\theta_\mathrm{crit}</math>:

:<math>\theta_{\mathrm{crit}} = \sin^{-1} \left( \frac{n_2}{n_1} \right)</math>

When θ1 > θcrit, no refracted ray appears, and the incident ray undergoes [[total internal reflection]] from the interface medium.

=== Derivations ===
Snell's law may be derived from [[Fermat's principle]], which states that the light travels the path which takes the least time. By taking the [[derivative]] of the [[optical path length]], the [[stationary point]] is found giving the path taken by the light (though it should be noted that the result does not show light taking the least time path, but rather one that is stationary with respect to small variations as there are cases where light actually takes the greatest time path, as in a spherical mirror).

Alternatively, Snell's law can be derived using interference of all possible paths of light wave from source to observer—it results in destructive interference everywhere except extrema of phase (where interference is constructive)—which become actual paths. In a classic analogy by [[Richard Feynman]], the area of lower refractive index is replaced by a beach, the area of higher refractive index by the sea, and the fastest way for a rescuer on the beach to get to a [[drowning]] person in the sea is to run along a path that follows Snell's law.

Another way to derive Snell’s Law involves an application of the general [[boundary conditions]] of [[Maxwell equations]] for [[electromagnetic radiation]].

== Uses ==
=== Calculating refractive indices ===

In the diagram on the right, two media of refractive indices ''n''1 (on the left) and ''n''2 (on the right) meet at a surface or interface (vertical line). ''n''2 > ''n''1, and light has a slower [[phase velocity]] within the second medium.

A light ray '''PO''' in the leftmost medium strikes the interface at the point '''O'''. From point '''O''', we project a straight line at right angles to the line of the interface; this is known as the [[Surface normal|normal]] to the surface (horizontal line). The angle between the normal and the light ray '''PO''' is known as the ''angle of incidence'', θ1.

The ray continues through the interface into the medium on the right; this is shown as the ray '''OQ'''. The angle it makes to the normal is known as the ''angle of refraction'', θ2.

:<math>n_1 \sin\theta_1 = n_2 \sin\theta_2 </math> or <math>\sum_{k=x,y}^N x=n_x\sin\theta_x,n_y \sin\theta_y</math>
:<math>\frac{n_1}{n_2} = \frac{\sin\theta_2}{\sin\theta_1}</math>
Note that, for the case of θ1 = 0° (i.e., a ray perpendicular to the interface) the solution is θ2 = 0° regardless of the values of ''n''1 and ''n''2-- a ray entering a medium perpendicular to the surface is never bent.

The above is also valid for light going from a dense to a less dense medium; the symmetry of Snell's law shows that the same ray paths are applicable in opposite direction.

A qualitative rule for determining the direction of refraction is that the ray in the denser medium is always closer to the normal. An analogy often used to remember this is done by visualizing the ray as a car crossing the boundary between asphalt (the less dense medium) and mud (the denser medium). Depending on the angle, either the left wheel or the right wheel of the car will cross into the new medium first, causing the car to swerve.

=== Vector form ===

Given a normalized ray vector '''v''' and a normalized plane normal vector '''p''', one can work out the normalized reflected and refracted rays: (note that the actual angles θ1 and θ2 are not worked out)

:<math>\cos\theta_1=\mathbf{v}\cdot\mathbf{p}</math>
:<math>\cos\theta_2=\sqrt{1-\left(\frac{n_1}{n_2}\right)^2\left(1-\left(\cos\theta_1\right)^2\right)}</math>
:<math>\mathbf{v}_{\mathrm{reflect}}=\mathbf{v}-\left(2\cos\theta_1\right)\mathbf{p}</math>
:<math>\mathbf{v}_{\mathrm{refract}}=\left(\frac{n_1}{n_2}\right)\mathbf{v} + \left(\cos\theta_2 - \frac{n_1}{n_2}\cos\theta_1\right)\mathbf{p}</math>
Note: <math>\mathbf{v}\cdot\mathbf{p}</math> must be positive.

The cosines may be recycled and used in the [[Fresnel equations]] for working out the intensity of the resulting rays. During total internal reflection an [[evanescent wave]] is produced, which [[exponential decay|rapidly decays]] from the surface into the second medium. Conservation of energy is maintained by the circulation of energy across the boundary, averaging to zero net energy transmission.

==Dispersion==

In many wave-propagation media, wave velocity changes with frequency or wavelength of the waves; this is true of light propagation in most transparent substances other than a vacuum. These media are called dispersive. The result is that the angles determined by Snell's law also depend on frequency or wavelength, so that a ray of mixed wavelengths, such as white light, will spread or disperse. Such dispersion of light in glass or water underlies the origin of [[rainbow]]s, since different wavelenghts appear as different colors.

In optical instruments, [[dispersion (optics)|dispersion]] leads to [[chromatic aberration]], a color-dependent blurring that sometimes is the resolution-limiting effect. This was especially true in [[refracting telescope]]s, before the invention of achromatic objective lenses.

==See also==

* [[Fresnel equations]]
* [[Reflection (physics)|Reflection]]
* [[Refraction]]
* [[Total internal reflection]]
* [[Evanescent wave]]

==References==

<references />

== External links ==

* [http://mintaka.sdsu.edu/GF/explain/optics/discovery.html Discovery of the law of refraction]

[[Category:Geometrical optics]]
[[Category:Introductory physics]]
[[Category:Eponymous laws]]

[[cs:Snellův zákon]]
[[de:Snelliussches Brechungsgesetz]]
[[es:Ley de Snell]]
[[fr:Lois de Snell-Descartes]]
[[it:Legge di Snell]]
[[he:חוק סנל]]
[[nl:Wet van Snellius]]
[[ja:スネルの法則]]
[[no:Snells brytningslov]]
[[pl:Prawo Snelliusa]]
[[ru:Закон Снелла]]
[[sl:Lomni zakon]]
[[sv:Snells lag]]
[[zh:光的折射定律]]

Snell's law

2007-01-15T20:09:15Z

JSpudeman: Fixed up intro slightly; condensed it into meaty first paragraph. STILL NEEDS REFERENCES -- image is uneccesary, just reference the damn book.

[[Image:Snells law.svg|thumb|300px|[[Refraction]] of light at the interface between two media of different [[refractive index|refractive indices]], with n2 > n1. Since the velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.]]

In [[optics]] and [[physics]], '''Snell's law''' (also known as '''Descartes' Law''' or the '''law of refraction'''), is a [[mathematical formula|formula]], which used to describe the relationship between the [[sine]]s of angles of incidence and refraction as constant, when referring to light or other [[wave]], passing through a boundary between two or more different [[isotropic]] [[medium (optics)|media]], such as air or glass. In it's modern forms, the law can be manipulated to identify the angles of [[angle of incidence|incidence]] or [[angle of refraction|refraction]], and can be further used to identify the [[refractive index]] of a material.

Named for one of it's discoverers, [[Willebrord Snellius]], Snell's aw follows from [[Pierre de Fermat]]'s [[Fermat's principle|principle of least time]], which states that the ratio of the [[sine]]s of the angles of incidence and refraction is equal to the ratio of [[velocities]] in the two media, or equivalently the inverse ratio of the indices of refraction:

{| cellspacing="10"
|<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{n_2}{n_1}</math>
| or
|<math>n_1\sin\theta_1 = n_2\sin\theta_2</math>
|}
== History ==
[[Image:Snell Law of Sines 1837.png|thumb|right|300px|An 1837 view of the history of "the Law of the Sines"<ref>William Whewell, ''History of the Inductive Science from the Earliest to the Present Times'', London: John H. Parker, 1837.</ref>]]
Snell's law was first discovered and described by [[Ibn Sahl]] in a manuscript written c.[[984]],<ref>{{cite journal | author=Rashed, Roshdi | title= A pioneer in anaclastics: Ibn Sahl on burning mirrors and lenses | journal= [[Isis (journal)|Isis]]| year= 1990| volume= 81| pages= 464–491 |doi=10.1086/355456}}</ref> who used it to work out the shapes of lenses that focus light with no geometric aberrations, known as [[anaclastic lens]]es. It was discovered again by [[Thomas Harriot]] in [[1602]],<ref>{{cite journal | author=Kwan, A., Dudley, J., and Lantz, E. | title=Who really discovered Snell's law? | journal=[[Physics World]] | year=2002 | volume=15 | issue=4 | pages=64 |url=http://physicsworldarchive.iop.org/index.cfm?action=summary&doc=15%2F4%2Fphwv15i4a44%40pwa-xml&qt=}}</ref> who did not publish his work.

In [[1621]], it was discovered yet again by Willebrord Snel, in a mathematically equivalent form, but unpublished during his lifetime. [[René Descartes]] independently derived the law using heuristic momentum conservation arguments in terms of sines in his [[1637]] treatise ''[[Discourse on Method]]'' (though detractors such as Fermat accused Descartes of working toward the already known answer with sophistic reasoning), and used it to solve a range of optical problems. Rejecting Descartes' solution, Pierre de Fermat arrived at the same solution based solely on his principal of least time.

In [[French language|French]], Snell's Law is called "la loi de Descartes" or "loi de Snell-Descartes."

== Explanation ==
Snell's law is used to determine the direction of light rays though refractive media with varying indices of refraction. The indices of refraction of the media, labeled <math>n_1,n_2</math> and so on, are used to represent the factor by which light is "slowed down" within a refractive medium, such as glass or water, compared to its velocity in a vacuum.

As light passes the border between media, depending upon the relative refractive indices of the two media, the light will either be refracted to a lesser angle, or a greater one. These angles are measured with respect to the ''normal line'', the perpendicular to the boundary. In the case of light traveling from air into water, light would be refrated towards the normal line, due to the fact that the light is slowed down in water; light traveling from water to air would refract away from the normal line.

Refraction between two surfaces is also referred to as ''reversible'' due to the fact that if all conditions were identical, the angles would be the same for light propagating in the opposite direction.

Snell's law is only generally true for isotropic media (such as [[glass]]). In [[anisotropic]] media such as some [[crystal]]s, [[birefringence]] may split the refracted ray into two rays, the ''ordinary'' or ''o''-ray which follows Snell's law, and the other ''extraordinary'' or ''e''-ray which may not be co-planar with the incident ray.

When the light or other wave involved is monochromatic, that is, of a single frequency, Snell's law can also be expressed in terms of a ratio of wavelengths in the two media, λ1 and λ2:

:<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{\lambda_1}{\lambda_2}</math>

=== Total internal reflection ===
[[Image:Refraction internal reflection diagram.PNG|thumb|220px|right|An example of the angles involved within total internal reflection.]]
When light moves from a dense to a less dense medium, such as from water to air, Snell's law cannot be used to calculate the refracted angle when the resolved sine value is higher than 1. At this point, light is reflected in the incident medium, known as internal reflection. Before the ray totally internally reflects, the light refracts at the '''critical angle'''; it travels directly along the surface between the two refractive media, without a change in phases like in other forms of optical phenomena.

As an example, a ray of light is incident at <math>50^o</math> towards a water–air boundary. If the angle is calculated using Snell's Law, then the resulting sine value will not invert, and thus the refracted angle cannot be calculated:

:<math>\theta_2 = \sin^{-1} (\frac{n_1}{n_2}\sin\theta_1) = \sin^{-1} (\frac{1.333}{1.000}0.766) = \sin^{-1} 1.021</math>

Snell's Law cannot calculate such angles because there is no refracted outgoing ray.

In order to calculate the critical angle, let <math>\theta_2 = 90^o</math> and solve for <math>\theta_\mathrm{crit}</math>:

:<math>\theta_{\mathrm{crit}} = \sin^{-1} \left( \frac{n_2}{n_1} \right)</math>

When θ1 > θcrit, no refracted ray appears, and the incident ray undergoes [[total internal reflection]] from the interface medium.

=== Derivations ===
Snell's law may be derived from [[Fermat's principle]], which states that the light travels the path which takes the least time. By taking the [[derivative]] of the [[optical path length]], the [[stationary point]] is found giving the path taken by the light (though it should be noted that the result does not show light taking the least time path, but rather one that is stationary with respect to small variations as there are cases where light actually takes the greatest time path, as in a spherical mirror).

Alternatively, Snell's law can be derived using interference of all possible paths of light wave from source to observer—it results in destructive interference everywhere except extrema of phase (where interference is constructive)—which become actual paths. In a classic analogy by [[Richard Feynman]], the area of lower refractive index is replaced by a beach, the area of higher refractive index by the sea, and the fastest way for a rescuer on the beach to get to a [[drowning]] person in the sea is to run along a path that follows Snell's law.

Another way to derive Snell’s Law involves an application of the general [[boundary conditions]] of [[Maxwell equations]] for [[electromagnetic radiation]].

== Uses ==
=== Calculating refractive indices ===

In the diagram on the right, two media of refractive indices ''n''1 (on the left) and ''n''2 (on the right) meet at a surface or interface (vertical line). ''n''2 > ''n''1, and light has a slower [[phase velocity]] within the second medium.

A light ray '''PO''' in the leftmost medium strikes the interface at the point '''O'''. From point '''O''', we project a straight line at right angles to the line of the interface; this is known as the [[Surface normal|normal]] to the surface (horizontal line). The angle between the normal and the light ray '''PO''' is known as the ''angle of incidence'', θ1.

The ray continues through the interface into the medium on the right; this is shown as the ray '''OQ'''. The angle it makes to the normal is known as the ''angle of refraction'', θ2.

:<math>n_1 \sin\theta_1 = n_2 \sin\theta_2 </math> or <math>\sum_{k=x,y}^N x=n_x\sin\theta_x,n_y \sin\theta_y</math>
:<math>\frac{n_1}{n_2} = \frac{\sin\theta_2}{\sin\theta_1}</math>
Note that, for the case of θ1 = 0° (i.e., a ray perpendicular to the interface) the solution is θ2 = 0° regardless of the values of ''n''1 and ''n''2-- a ray entering a medium perpendicular to the surface is never bent.

The above is also valid for light going from a dense to a less dense medium; the symmetry of Snell's law shows that the same ray paths are applicable in opposite direction.

A qualitative rule for determining the direction of refraction is that the ray in the denser medium is always closer to the normal. An analogy often used to remember this is done by visualizing the ray as a car crossing the boundary between asphalt (the less dense medium) and mud (the denser medium). Depending on the angle, either the left wheel or the right wheel of the car will cross into the new medium first, causing the car to swerve.

=== Vector form ===

Given a normalized ray vector '''v''' and a normalized plane normal vector '''p''', one can work out the normalized reflected and refracted rays: (note that the actual angles θ1 and θ2 are not worked out)

:<math>\cos\theta_1=\mathbf{v}\cdot\mathbf{p}</math>
:<math>\cos\theta_2=\sqrt{1-\left(\frac{n_1}{n_2}\right)^2\left(1-\left(\cos\theta_1\right)^2\right)}</math>
:<math>\mathbf{v}_{\mathrm{reflect}}=\mathbf{v}-\left(2\cos\theta_1\right)\mathbf{p}</math>
:<math>\mathbf{v}_{\mathrm{refract}}=\left(\frac{n_1}{n_2}\right)\mathbf{v} + \left(\cos\theta_2 - \frac{n_1}{n_2}\cos\theta_1\right)\mathbf{p}</math>
Note: <math>\mathbf{v}\cdot\mathbf{p}</math> must be positive.

The cosines may be recycled and used in the [[Fresnel equations]] for working out the intensity of the resulting rays. During total internal reflection an [[evanescent wave]] is produced, which [[exponential decay|rapidly decays]] from the surface into the second medium. Conservation of energy is maintained by the circulation of energy across the boundary, averaging to zero net energy transmission.

==Dispersion==

In many wave-propagation media, wave velocity changes with frequency or wavelength of the waves; this is true of light propagation in most transparent substances other than a vacuum. These media are called dispersive. The result is that the angles determined by Snell's law also depend on frequency or wavelength, so that a ray of mixed wavelengths, such as white light, will spread or disperse. Such dispersion of light in glass or water underlies the origin of [[rainbow]]s, since different wavelenghts appear as different colors.

In optical instruments, [[dispersion (optics)|dispersion]] leads to [[chromatic aberration]], a color-dependent blurring that sometimes is the resolution-limiting effect. This was especially true in [[refracting telescope]]s, before the invention of achromatic objective lenses.

==See also==

* [[Fresnel equations]]
* [[Reflection (physics)|Reflection]]
* [[Refraction]]
* [[Total internal reflection]]
* [[Evanescent wave]]

==References==

<references />

== External links ==

* [http://mintaka.sdsu.edu/GF/explain/optics/discovery.html Discovery of the law of refraction]

[[Category:Geometrical optics]]
[[Category:Introductory physics]]
[[Category:Eponymous laws]]

[[cs:Snellův zákon]]
[[de:Snelliussches Brechungsgesetz]]
[[es:Ley de Snell]]
[[fr:Lois de Snell-Descartes]]
[[it:Legge di Snell]]
[[he:חוק סנל]]
[[nl:Wet van Snellius]]
[[ja:スネルの法則]]
[[no:Snells brytningslov]]
[[pl:Prawo Snelliusa]]
[[ru:Закон Снелла]]
[[sl:Lomni zakon]]
[[sv:Snells lag]]
[[zh:光的折射定律]]

Photoelectric effect

2007-01-12T12:13:33Z

JSpudeman: Typo city today :-/

[[Image:Photoelectric_effect.png|thumb|right|275px|A diagram illustrating the emission of photoelectrons from a negatively charged plate, requiring energy gained from an incoming photon to be more than the work function of the material. A positively charged plate would require a higher frequency due to attraction between the nuclei and electrons.]]
The '''photoelectric effect''' is a [[quantum mechanics|quantum]] [[electrical]] phenomenon in which, [[electron|photoelectrons]] are emitted from matter after the absorption of energy from [[electromagnetic wave|electromagnetic radiation]] such as [[x-rays]].<ref name="serway_1">''Serway, R. S.(1990), p1150''' Describes the photoelectric effect as the "Emission of photoelectrons from matter", and describes the original usage as the "Emission of Photoelectrons from metallic surfaces" after the experiments of Milikan, and others.</ref> The effect is also termed the '''Hertz Effect'''<ref>''[http://scienceworld.wolfram.com/physics/HertzEffect.html Wolfram Scienceworld]'' describes the terminology of the photoelectric effect and the previous usage of the term '''Hertz Effect'''.</ref>, due to it's discovery by [[Heinrich Rudolf Hertz]], although the term has generally fallen out of use in more current terminology. The photoelectric effect is considered to be an important step towards understanding the nature of light, due to serveral attempts to explain it using both [[wave theory|wave]] and [[particle|particulate]] theories and is thought to have influenced the formation of [[wave-particle duality]]. <ref name="serway_1" />

==Introduction==

Upon exposing a [[metal|metallic]] surface to electromagnetic radiation that is above a [[threshold]] frequency or threshold wavelength (which is specific to the type of surface and material), the photons are absorbed and [[Current (electricity)|current]] is produced. No electrons are emitted for radiation with a frequency below that of the threshold, as the electrons are unable to gain sufficient energy to overcome the electrostatic barrier presented by the termination of the crystalline surface (the material's [[work function]]). In 1905 it was known that the energy of the photoelectrons increased with increasing frequency of incident light, but the manner of the increase was not experimentally determined to be linear until 1915 when [[Robert Millikan|Robert Andrews Millikan]] showed that Einstein was correct.<ref>{{cite journal| first=Robert Andrews| last=Millikan| journal=Physical Review| volume=VII| pages=362| year=1916}}</ref>

By conservation of energy, the energy of the photon is absorbed by the electron and, if sufficient, the electron can escape from the material with a finite kinetic energy. A single photon can only eject a single electron, as the energy of one photon may only be absorbed by one electron. The electrons that are emitted are often termed '''photoelectrons'''.

The photoelectric effect helped further [[wave-particle duality]], whereby physical systems (such as [[photon]]s, in this case) display both wave-like and particle-like properties and behaviours, a concept that was used by the creators of [[quantum mechanics]]. The photoelectric effect was explained mathematically by [[Albert Einstein]], who extended the work on quanta developed by [[Max Planck]].

== Explanation ==

The photons of the light beam have a characteristic energy given by the wavelength of the light. In the photoemission process, if an electron absorbs the energy of one photon and has more energy than the [[work function]], it is ejected from the material. If the photon energy is too low, however, the electron is unable to escape the surface of the material. Increasing the intensity of the light beam does not change the energy of the constituent photons, only their number, and thus the energy of the emitted electrons does not depend on the intensity of the incoming light.

Electrons can absorb energy from photons when irradiated, but they follow an "all or nothing" principle. All of the energy from one photon must be absorbed and used to liberate one electron from atomic binding, or the energy is re-emitted. If the photon is absorbed, some of the energy is used to liberate it from the atom, and the rest contributes to the electron's kinetic (moving) energy as a free particle.

===Equations===

In analysing the photoelectric effect quantitatively using Einstein's method, the following equivalent equations are used:

Energy of [[photon]] = Energy needed to remove an [[electron]] + [[Kinetic energy]] of the emitted electron

Algebraically:
:<math>hf = \phi + E_{k_{max}} \,</math>
where
* ''h'' is [[Planck's constant]],
* ''f'' is the frequency of the incident photon,
* <math>\phi = h f_0 \ </math> is the [[work function]], or minimum energy required to remove an electron from atomic binding,
* <math>E_{k_{max}} = \frac{1}{2} m v_m^2 </math> is the maximum kinetic energy of ejected electrons,
* ''f''0 is the threshold [[frequency]] for the photoelectric effect to occur,
* ''m'' is the rest mass of the ejected electron, and
* ''<math> v_m </math>'' is the velocity of the ejected electron.

''Note'': If the photon's energy (''hf'') is not greater than the work function (<math>\phi</math>), no electron will be emitted. The work function is sometimes denoted <math>W</math>.
According to Einstein's special theory of relativity the relation between energy (E) and momentum (p) of a particle is <math>E = \sqrt{(pc)^2 + (mc^2)^2}</math>, where m is the rest mass of the particle and c is the velocity of light in a vacuum.

==History==
===Early observations===

In 1839, [[A. E. Becquerel|Alexandre Edmond Becquerel]] observed the photoelectric effect via an electrode in a conductive solution exposed to light. In [[1873]], [[Willoughby Smith]] found that [[selenium]] is photoconductive.

===Hertz's spark gaps===

[[Heinrich Hertz]], in 1887, made observations of the photoelectric effect and of the production and reception of electromagnetic (EM) waves, published in the journal [[Annalen der Physik]]. His receiver consisted of a coil with a [[spark gap]], whereupon a spark would be seen upon detection of EM waves. He placed the apparatus in a darkened box in order to see the spark better; he observed, however, that the maximum spark length was reduced when in the box. A glass panel placed between the source of EM waves and the receiver absorbed ultraviolet radiation that assisted the electrons in jumping across the gap. When removed, the spark length would increase. He observed no decrease in spark length when he substituted quartz for glass, as [[quartz]] does not absorb UV radiation.

Hertz concluded his months of investigation and reported the results obtained. He did not further pursue investigation of this effect, nor did he make any attempt at explaining how the observed phenomenon was brought about.

===JJ Thomson: electrons===

In 1899, [[Joseph John Thomson]] investigated [[ultraviolet light]] in [[Geissler tube|Crookes tube]]s. Influenced by the work of [[James Clerk Maxwell]], Thomson deduced that cathode rays consisted of negatively charged particles, later called electrons, which he called "corpuscles". In the research, Thomson enclosed a metal plate (a cathode) in a vacuum tube, and exposed it to high frequency radiation. It was thought that the oscillating electromagnetic fields caused the atoms' field to resonate and, after reaching a certain amplitude, caused a subatomic "corpuscle" to be emitted, and current to be detected. The amount of this current varied with the intensity and color of the radiation. Larger radiation intensity or frequency would produce more current.

=== Von Lenard's observations ===

In 1902, [[Philipp Eduard Anton von Lenard|Philipp von Lenard]] observed the variation in electron energy with light frequency.<ref>http://www.phys.virginia.edu/classes/252/photoelectric_effect.html</ref> He used a powerful electric arc lamp which enabled him to investigate large changes in intensity, and had sufficient power to enable him to investigate the variation of potential with light frequency. His experiment directly measured potentials, not electron kinetic energy: he found the electron energy by relating it to the maximum stopping potential (voltage) in a phototube. He found that the calculated maximum electron [[kinetic energy]] is determined by the frequency of the light. For example, an increase in frequency results in an increase in the maximum kinetic energy calculated for an electron upon liberation - [[ultraviolet radiation]] would require a higher applied stopping potential to stop current in a phototube than blue light. However Lenard's results were qualitative rather than quantitative because of the difficulty in performing the experiments: the experiments needed to be done on freshly cut metal so that the pure metal was observed, but it oxidised in a matter of minutes even in the partial vacuums he used. The current emitted by the surface was determined by the light's intensity, or brightness: doubling the intensity of the light doubled the number of electrons emitted from the surface. Lenard did not know of photons.

===Einstein: light quanta===

[[Albert Einstein]]'s mathematical description in 1905 of how it was caused by absorption of what were later called [[photon]]s, or [[quantum mechanics|quanta]] of light, in the interaction of light with the [[electron]]s in the substance, was contained in the paper named "''On a Heuristic Viewpoint Concerning the Production and Transformation of Light''". This paper proposed the simple description of "light quanta" (later called "''photons''") and showed how they could be used to explain such phenomena as the photoelectric effect. The simple explanation by Einstein in terms of absorption of single [[quanta]] of light explained the features of the phenomenon and helped explain the characteristic frequency. Einstein's explanation of the photoelectric effect won him the [[Nobel Prize]] (in Physics) of 1921.

The idea of light quanta was motivated by [[Max Planck]]'s published law of [[black-body radiation]] ("''On the Law of Distribution of Energy in the Normal Spectrum''". Annalen der Physik 4 (1901)) by assuming that Hertzian oscillators could only exist at energies E proportional to the frequency f of the oscillator by E = hf, where h is Planck's constant. Einstein, by assuming that light actually ''consisted'' of discrete energy packets, wrote an equation for the photoelectric effect that fit experiments (it explained why the energy of the photoelectrons was dependent only on the ''frequency'' of the incident light and not on its ''intensity'': a low intensity, high frequency source could supply a few high energy photons, whereas a high intensity, low frequency source would supply no photons of sufficient individual energy to dislodge any electrons). This was an enormous theoretical leap and the reality of the light quanta was strongly resisted. The idea of light quanta contradicted the wave theory of light that followed naturally from [[James Clerk Maxwell]]'s equations for electromagnetic behavior and, more generally, the assumption of [[infinite divisibility]] of energy in physical systems. Even after experiments showed that Einstein's equations for the photoelectric effect were accurate there was resistance to the idea of photons, since it appeared to contradict Maxwell's equations, which were believed to be well understood and well verified.

Einstein's work predicted that the energy of the ejected electrons would increase linearly with the frequency of the light. Perhaps surprisingly, that had not yet been tested. In 1905 it was known that the energy of the photoelectrons increased with increasing ''frequency'' of incident light -- and independent of the ''intensity'' of the light -- but the manner of the increase was not experimentally determined to be linear until 1915 when [[Robert Andrews Millikan]] showed that Einstein was correct.<ref>http://spiff.rit.edu/classes/phys314/lectures/photoe/photoe.html</ref>

=== Effect on wave-particle question ===

The photoelectric effect helped propel the then-emerging concept of the dual nature of [[light]], that light exhibits characteristics of waves and particles at different times. The effect was impossible to understand in terms of the classical [[wave]] description of light, as the energy of the emitted electrons did not depend on the intensity of the incident radiation. Classical theory predicted that the electrons could 'gather up' energy over a period of time, and then be emitted. For such a classical theory to work a pre-loaded state would need to persist in matter. The idea of the pre-loaded state was discussed in Millikan's book ''Electrons (+ & -)'' and in Compton and Allison's book ''X-Rays in Theory and Experiment''. These ideas were abandoned.

==Uses and effects==

===Photodiodes===
[[Solar cell]]s (used in [[solar power]]) and [[Photodiode|light-sensitive diodes]] use a variant of the photoelectric effect, but not ejecting electrons out of the material. In [[semiconductor]]s, light of even relatively low energy, such as visible photons, can kick electrons out of the [[valence band]] and into the higher-energy [[conduction band]], where they can be harnessed, creating [[electric current]] at a voltage related to the [[bandgap]] energy.

===Electroscopes===
[[Electroscope]]s are fork-shaped, hinged metallic leaves placed in a vacuum jar, partially exposed to the outside environment. When an electroscope is charged positively or negatively, the two leaves separate, as charge distributes evenly along the leaves causing repulsion between two like poles. When ultraviolet radiation (or any radiation above threshold frequency) shines onto the metallic outside of the electroscope, a negatively charged scope will discharge and the leaves will collapse, while nothing will happen to a positively charged scope (besides [[charge decay]]). The reason is that electrons will be liberated from the negatively charged one, gradually making it neutral, while liberating electrons from the positively charged one will make it even more positive, keeping the leaves apart

===Photoelectron spectroscopy===
Since the energy of the photoelectrons emitted is exactly the energy of the incident photon minus the material's work function or binding energy, the work function of a sample can be determined by bombarding it with a [[monochromatic]] [[X-ray]] source or [[UV]] source (typically a [[helium]] discharge lamp), and measuring the kinetic energy distribution of the electrons emitted.

This must be done in a high [[vacuum]] environment, since the electrons would be scattered by air.

A typical electron energy analyzer is a concentric hemispherical analyser (CHA), which uses an electric field to divert electrons different amounts depending on their kinetic energies. For every element and core [[atomic orbital]] there will be a different binding energy. The many electrons created from each will then show up as spikes in the analyzer, and can be used to determine the elemental composition of the sample.<ref>[http://www.chem.qmw.ac.uk/surfaces/scc/scat5_3.htm Photoelectron spectroscopy]</ref>

===Spacecraft===
The photoelectric effect will cause [[spacecraft]] exposed to sunlight to develop a positive charge. This can get up to the tens of [[volt]]s. This can be a major problem, as other parts of the spacecraft in shadow develop a negative charge (up to several kilovolts) from nearby plasma, and the imbalance can discharge through delicate electrical components. The [[static electricity|static charge]] created by the photoelectric effect is self-limiting, though, because a more highly-charged object gives up its electrons less easily.<ref>[http://www.eas.asu.edu/~holbert/eee460/spc-chrg.html Spacecraft charging]</ref>

===Moon dust===
Light from the sun hitting lunar dust causes it to become charged through the photoelectric effect. The charged dust then repels itself and lifts off the surface of the [[Moon]] by [[electrostatic levitation]]. This manifests itself almost like an "atmosphere of dust", visible as a thin haze and blurring of distant features, and visible as a dim glow after the sun has set. This was first photographed by the [[Surveyor program]] probes in the 1960s. It is thought that the smallest particles are repelled up to kilometers high, and that the particles move in "fountains" as they charge and discharge.<ref>- [http://www.firstscience.com/site/articles/moonfountains.asp Moon fountains]</ref><ref>- [http://www.spacer.com/news/dust-00a.html Dust gets a charge in a vacuum]</ref>

==See also==
<table style="text-align: left; width: 100%;" border="0" cellspacing="2"
cellpadding="2">
<tr>
<td style="vertical-align: top;">
''[[Electronics]]:''
* [[Photocurrent]]
* [[Photomultiplier]]
* [[Solar cell]]
* [[Solar power]]
* [[Transducer]]

''[[Physics]]:''
* [[Atom]]
* [[Corona discharge]]
* [[Double-slit experiment]]
* [[Electron]]
* [[Gamma ray]]
* [[Nobel Prize in Physics]]
* [[Optical phenomenon]]
* [[Planck's law of black body radiation]]
* [[Photon]]
* [[Photon dynamics in the double-slit experiment]]
* [[Photon polarization]]
* [[Quantum mechanics]]
* [[Radiant energy]]
* [[Wave-particle duality]]
</td>
<td style="vertical-align: top;">
</td>
<td style="vertical-align: top;">
''People'':
* [[Aleksandr Grigorievich Stoletov]]
* [[Albert Einstein]]
* [[Heinrich Hertz]]
* [[Ernest Lawrence]]
* [[Robert Millikan]]
* [[Max Planck]]
* [[Joseph John Thomson]]

''Lists'':

* [[List of electronics topics]]
* [[List of optical topics]]
* [[List of physics topics]]
* [[Timeline of solar cells]]
* [[List of topics (scientific method)|Scientific method list]]
* [[Timeline of quantum mechanics, molecular physics, atomic physics, nuclear physics, and particle physics|Timeline of mechanics and physics]]
</td>
</tr>
</table>

== References ==
=== Notes ===
<references />

=== Book References ===
Serway, R. A. (1990). ''Physics for engineers and scientists'', 3rd ed. Saunders Publishing

==External links==
{{Commons|Photoelectric effect}}
* Nave, R., "''[http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html Wave-Particle Duality]''". HyperPhysics.
* Jpaul's "''[http://www.students.uiuc.edu/~jpaul/theory.htm Photovoltaics: Theory and Practice]''". [http://www.students.uiuc.edu/~jpaul/photoelectric.htm Photoelectric effect].
* "''[http://www.colorado.edu/physics/2000/quantumzone/photoelectric.html Photoelectric effect]''". Physics 2000. University of Colorado, Boulder, Colorado.
* ACEPT W3 Group, "''[http://acept.la.asu.edu/PiN/rdg/photoelectric/photoelectric.shtml The Photoelectric Effect]''". Department of Physics and Astronomy, Arizona State University, Tempe, AZ.
* Haberkern, Thomas, and N Deepak "''[http://www.faqs.org/docs/qp/ Grains of Mystique: Quantum Physics for the Layman]''". [http://www.faqs.org/docs/qp/chap03.html Einstein Demystifies Photoelectric Effect], Chapter 3.
* Department of Physics, "''[http://www.phy.davidson.edu/ModernPhysicsLabs/hovere.html The Photoelectric effect]''". Physics 320 Laboratory, Davidson College, Davidson.
* Fowler, Michael, "''[http://www.phys.virginia.edu/classes/252/photoelectric_effect.html The Photoelectric Effect]''". Physics 252, University of Virginia.
* Brandl, Michael, "[http://35.9.69.219/home/modules/pdf_modules/m213.pdf MISN-0-213 ''The Photoelectric Effect'']" ([[Portable Document Format|PDF file]]), [http://www.physnet.org Project PHYSNET].
* [http://cinarz.zdo.com/moodle/mod/resource/view.php?id=15 Quantum Chemistry I Lecture ]

''[[Applet]]s''
* Curull, Xavi Espinal, "''[http://www.ifae.es/xec/phot2.html Photoelectric effect Applet]''". ([[Java (programming language)|Java]])
* Fendt, Walter, and Taha Mzoughi, "''[http://www.walter-fendt.de/ph14e/photoeffect.htm The Photoelectric Effect]''". ([[Java (programming language)|Java]])
* "''[http://lectureonline.cl.msu.edu/~mmp/kap28/PhotoEffect/photo.htm Applet: Photo Effect]''". Open Source Distributed Learning Content Management and Assessment System. ([[Java (programming language)|Java]])

[[Category:Foundational quantum physics]]
[[Category:Electrical phenomena]]
[[Category:Albert Einstein]]

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Photoelectric effect

2007-01-12T12:12:52Z

JSpudeman: While the tf is still acceptable, it's easier to use work function in terms of grammar

[[Image:Photoelectric_effect.png|thumb|right|275px|A diagram illustrating the emission of photoelectrons from a negatively charged plate, requiring energy gained from an incoming photon to be more than the work function of the material. A positively charged plate would require a larger frequency due to attraction between the nuclei and electrons.]]
The '''photoelectric effect''' is a [[quantum mechanics|quantum]] [[electrical]] phenomenon in which, [[electron|photoelectrons]] are emitted from matter after the absorption of energy from [[electromagnetic wave|electromagnetic radiation]] such as [[x-rays]].<ref name="serway_1">''Serway, R. S.(1990), p1150''' Describes the photoelectric effect as the "Emission of photoelectrons from matter", and describes the original usage as the "Emission of Photoelectrons from metallic surfaces" after the experiments of Milikan, and others.</ref> The effect is also termed the '''Hertz Effect'''<ref>''[http://scienceworld.wolfram.com/physics/HertzEffect.html Wolfram Scienceworld]'' describes the terminology of the photoelectric effect and the previous usage of the term '''Hertz Effect'''.</ref>, due to it's discovery by [[Heinrich Rudolf Hertz]], although the term has generally fallen out of use in more current terminology. The photoelectric effect is considered to be an important step towards understanding the nature of light, due to serveral attempts to explain it using both [[wave theory|wave]] and [[particle|particulate]] theories and is thought to have influenced the formation of [[wave-particle duality]]. <ref name="serway_1" />

==Introduction==

Upon exposing a [[metal|metallic]] surface to electromagnetic radiation that is above a [[threshold]] frequency or threshold wavelength (which is specific to the type of surface and material), the photons are absorbed and [[Current (electricity)|current]] is produced. No electrons are emitted for radiation with a frequency below that of the threshold, as the electrons are unable to gain sufficient energy to overcome the electrostatic barrier presented by the termination of the crystalline surface (the material's [[work function]]). In 1905 it was known that the energy of the photoelectrons increased with increasing frequency of incident light, but the manner of the increase was not experimentally determined to be linear until 1915 when [[Robert Millikan|Robert Andrews Millikan]] showed that Einstein was correct.<ref>{{cite journal| first=Robert Andrews| last=Millikan| journal=Physical Review| volume=VII| pages=362| year=1916}}</ref>

By conservation of energy, the energy of the photon is absorbed by the electron and, if sufficient, the electron can escape from the material with a finite kinetic energy. A single photon can only eject a single electron, as the energy of one photon may only be absorbed by one electron. The electrons that are emitted are often termed '''photoelectrons'''.

The photoelectric effect helped further [[wave-particle duality]], whereby physical systems (such as [[photon]]s, in this case) display both wave-like and particle-like properties and behaviours, a concept that was used by the creators of [[quantum mechanics]]. The photoelectric effect was explained mathematically by [[Albert Einstein]], who extended the work on quanta developed by [[Max Planck]].

== Explanation ==

The photons of the light beam have a characteristic energy given by the wavelength of the light. In the photoemission process, if an electron absorbs the energy of one photon and has more energy than the [[work function]], it is ejected from the material. If the photon energy is too low, however, the electron is unable to escape the surface of the material. Increasing the intensity of the light beam does not change the energy of the constituent photons, only their number, and thus the energy of the emitted electrons does not depend on the intensity of the incoming light.

Electrons can absorb energy from photons when irradiated, but they follow an "all or nothing" principle. All of the energy from one photon must be absorbed and used to liberate one electron from atomic binding, or the energy is re-emitted. If the photon is absorbed, some of the energy is used to liberate it from the atom, and the rest contributes to the electron's kinetic (moving) energy as a free particle.

===Equations===

In analysing the photoelectric effect quantitatively using Einstein's method, the following equivalent equations are used:

Energy of [[photon]] = Energy needed to remove an [[electron]] + [[Kinetic energy]] of the emitted electron

Algebraically:
:<math>hf = \phi + E_{k_{max}} \,</math>
where
* ''h'' is [[Planck's constant]],
* ''f'' is the frequency of the incident photon,
* <math>\phi = h f_0 \ </math> is the [[work function]], or minimum energy required to remove an electron from atomic binding,
* <math>E_{k_{max}} = \frac{1}{2} m v_m^2 </math> is the maximum kinetic energy of ejected electrons,
* ''f''0 is the threshold [[frequency]] for the photoelectric effect to occur,
* ''m'' is the rest mass of the ejected electron, and
* ''<math> v_m </math>'' is the velocity of the ejected electron.

''Note'': If the photon's energy (''hf'') is not greater than the work function (<math>\phi</math>), no electron will be emitted. The work function is sometimes denoted <math>W</math>.
According to Einstein's special theory of relativity the relation between energy (E) and momentum (p) of a particle is <math>E = \sqrt{(pc)^2 + (mc^2)^2}</math>, where m is the rest mass of the particle and c is the velocity of light in a vacuum.

==History==
===Early observations===

In 1839, [[A. E. Becquerel|Alexandre Edmond Becquerel]] observed the photoelectric effect via an electrode in a conductive solution exposed to light. In [[1873]], [[Willoughby Smith]] found that [[selenium]] is photoconductive.

===Hertz's spark gaps===

[[Heinrich Hertz]], in 1887, made observations of the photoelectric effect and of the production and reception of electromagnetic (EM) waves, published in the journal [[Annalen der Physik]]. His receiver consisted of a coil with a [[spark gap]], whereupon a spark would be seen upon detection of EM waves. He placed the apparatus in a darkened box in order to see the spark better; he observed, however, that the maximum spark length was reduced when in the box. A glass panel placed between the source of EM waves and the receiver absorbed ultraviolet radiation that assisted the electrons in jumping across the gap. When removed, the spark length would increase. He observed no decrease in spark length when he substituted quartz for glass, as [[quartz]] does not absorb UV radiation.

Hertz concluded his months of investigation and reported the results obtained. He did not further pursue investigation of this effect, nor did he make any attempt at explaining how the observed phenomenon was brought about.

===JJ Thomson: electrons===

In 1899, [[Joseph John Thomson]] investigated [[ultraviolet light]] in [[Geissler tube|Crookes tube]]s. Influenced by the work of [[James Clerk Maxwell]], Thomson deduced that cathode rays consisted of negatively charged particles, later called electrons, which he called "corpuscles". In the research, Thomson enclosed a metal plate (a cathode) in a vacuum tube, and exposed it to high frequency radiation. It was thought that the oscillating electromagnetic fields caused the atoms' field to resonate and, after reaching a certain amplitude, caused a subatomic "corpuscle" to be emitted, and current to be detected. The amount of this current varied with the intensity and color of the radiation. Larger radiation intensity or frequency would produce more current.

=== Von Lenard's observations ===

In 1902, [[Philipp Eduard Anton von Lenard|Philipp von Lenard]] observed the variation in electron energy with light frequency.<ref>http://www.phys.virginia.edu/classes/252/photoelectric_effect.html</ref> He used a powerful electric arc lamp which enabled him to investigate large changes in intensity, and had sufficient power to enable him to investigate the variation of potential with light frequency. His experiment directly measured potentials, not electron kinetic energy: he found the electron energy by relating it to the maximum stopping potential (voltage) in a phototube. He found that the calculated maximum electron [[kinetic energy]] is determined by the frequency of the light. For example, an increase in frequency results in an increase in the maximum kinetic energy calculated for an electron upon liberation - [[ultraviolet radiation]] would require a higher applied stopping potential to stop current in a phototube than blue light. However Lenard's results were qualitative rather than quantitative because of the difficulty in performing the experiments: the experiments needed to be done on freshly cut metal so that the pure metal was observed, but it oxidised in a matter of minutes even in the partial vacuums he used. The current emitted by the surface was determined by the light's intensity, or brightness: doubling the intensity of the light doubled the number of electrons emitted from the surface. Lenard did not know of photons.

===Einstein: light quanta===

[[Albert Einstein]]'s mathematical description in 1905 of how it was caused by absorption of what were later called [[photon]]s, or [[quantum mechanics|quanta]] of light, in the interaction of light with the [[electron]]s in the substance, was contained in the paper named "''On a Heuristic Viewpoint Concerning the Production and Transformation of Light''". This paper proposed the simple description of "light quanta" (later called "''photons''") and showed how they could be used to explain such phenomena as the photoelectric effect. The simple explanation by Einstein in terms of absorption of single [[quanta]] of light explained the features of the phenomenon and helped explain the characteristic frequency. Einstein's explanation of the photoelectric effect won him the [[Nobel Prize]] (in Physics) of 1921.

The idea of light quanta was motivated by [[Max Planck]]'s published law of [[black-body radiation]] ("''On the Law of Distribution of Energy in the Normal Spectrum''". Annalen der Physik 4 (1901)) by assuming that Hertzian oscillators could only exist at energies E proportional to the frequency f of the oscillator by E = hf, where h is Planck's constant. Einstein, by assuming that light actually ''consisted'' of discrete energy packets, wrote an equation for the photoelectric effect that fit experiments (it explained why the energy of the photoelectrons was dependent only on the ''frequency'' of the incident light and not on its ''intensity'': a low intensity, high frequency source could supply a few high energy photons, whereas a high intensity, low frequency source would supply no photons of sufficient individual energy to dislodge any electrons). This was an enormous theoretical leap and the reality of the light quanta was strongly resisted. The idea of light quanta contradicted the wave theory of light that followed naturally from [[James Clerk Maxwell]]'s equations for electromagnetic behavior and, more generally, the assumption of [[infinite divisibility]] of energy in physical systems. Even after experiments showed that Einstein's equations for the photoelectric effect were accurate there was resistance to the idea of photons, since it appeared to contradict Maxwell's equations, which were believed to be well understood and well verified.

Einstein's work predicted that the energy of the ejected electrons would increase linearly with the frequency of the light. Perhaps surprisingly, that had not yet been tested. In 1905 it was known that the energy of the photoelectrons increased with increasing ''frequency'' of incident light -- and independent of the ''intensity'' of the light -- but the manner of the increase was not experimentally determined to be linear until 1915 when [[Robert Andrews Millikan]] showed that Einstein was correct.<ref>http://spiff.rit.edu/classes/phys314/lectures/photoe/photoe.html</ref>

=== Effect on wave-particle question ===

The photoelectric effect helped propel the then-emerging concept of the dual nature of [[light]], that light exhibits characteristics of waves and particles at different times. The effect was impossible to understand in terms of the classical [[wave]] description of light, as the energy of the emitted electrons did not depend on the intensity of the incident radiation. Classical theory predicted that the electrons could 'gather up' energy over a period of time, and then be emitted. For such a classical theory to work a pre-loaded state would need to persist in matter. The idea of the pre-loaded state was discussed in Millikan's book ''Electrons (+ & -)'' and in Compton and Allison's book ''X-Rays in Theory and Experiment''. These ideas were abandoned.

==Uses and effects==

===Photodiodes===
[[Solar cell]]s (used in [[solar power]]) and [[Photodiode|light-sensitive diodes]] use a variant of the photoelectric effect, but not ejecting electrons out of the material. In [[semiconductor]]s, light of even relatively low energy, such as visible photons, can kick electrons out of the [[valence band]] and into the higher-energy [[conduction band]], where they can be harnessed, creating [[electric current]] at a voltage related to the [[bandgap]] energy.

===Electroscopes===
[[Electroscope]]s are fork-shaped, hinged metallic leaves placed in a vacuum jar, partially exposed to the outside environment. When an electroscope is charged positively or negatively, the two leaves separate, as charge distributes evenly along the leaves causing repulsion between two like poles. When ultraviolet radiation (or any radiation above threshold frequency) shines onto the metallic outside of the electroscope, a negatively charged scope will discharge and the leaves will collapse, while nothing will happen to a positively charged scope (besides [[charge decay]]). The reason is that electrons will be liberated from the negatively charged one, gradually making it neutral, while liberating electrons from the positively charged one will make it even more positive, keeping the leaves apart

===Photoelectron spectroscopy===
Since the energy of the photoelectrons emitted is exactly the energy of the incident photon minus the material's work function or binding energy, the work function of a sample can be determined by bombarding it with a [[monochromatic]] [[X-ray]] source or [[UV]] source (typically a [[helium]] discharge lamp), and measuring the kinetic energy distribution of the electrons emitted.

This must be done in a high [[vacuum]] environment, since the electrons would be scattered by air.

A typical electron energy analyzer is a concentric hemispherical analyser (CHA), which uses an electric field to divert electrons different amounts depending on their kinetic energies. For every element and core [[atomic orbital]] there will be a different binding energy. The many electrons created from each will then show up as spikes in the analyzer, and can be used to determine the elemental composition of the sample.<ref>[http://www.chem.qmw.ac.uk/surfaces/scc/scat5_3.htm Photoelectron spectroscopy]</ref>

===Spacecraft===
The photoelectric effect will cause [[spacecraft]] exposed to sunlight to develop a positive charge. This can get up to the tens of [[volt]]s. This can be a major problem, as other parts of the spacecraft in shadow develop a negative charge (up to several kilovolts) from nearby plasma, and the imbalance can discharge through delicate electrical components. The [[static electricity|static charge]] created by the photoelectric effect is self-limiting, though, because a more highly-charged object gives up its electrons less easily.<ref>[http://www.eas.asu.edu/~holbert/eee460/spc-chrg.html Spacecraft charging]</ref>

===Moon dust===
Light from the sun hitting lunar dust causes it to become charged through the photoelectric effect. The charged dust then repels itself and lifts off the surface of the [[Moon]] by [[electrostatic levitation]]. This manifests itself almost like an "atmosphere of dust", visible as a thin haze and blurring of distant features, and visible as a dim glow after the sun has set. This was first photographed by the [[Surveyor program]] probes in the 1960s. It is thought that the smallest particles are repelled up to kilometers high, and that the particles move in "fountains" as they charge and discharge.<ref>- [http://www.firstscience.com/site/articles/moonfountains.asp Moon fountains]</ref><ref>- [http://www.spacer.com/news/dust-00a.html Dust gets a charge in a vacuum]</ref>

==See also==
<table style="text-align: left; width: 100%;" border="0" cellspacing="2"
cellpadding="2">
<tr>
<td style="vertical-align: top;">
''[[Electronics]]:''
* [[Photocurrent]]
* [[Photomultiplier]]
* [[Solar cell]]
* [[Solar power]]
* [[Transducer]]

''[[Physics]]:''
* [[Atom]]
* [[Corona discharge]]
* [[Double-slit experiment]]
* [[Electron]]
* [[Gamma ray]]
* [[Nobel Prize in Physics]]
* [[Optical phenomenon]]
* [[Planck's law of black body radiation]]
* [[Photon]]
* [[Photon dynamics in the double-slit experiment]]
* [[Photon polarization]]
* [[Quantum mechanics]]
* [[Radiant energy]]
* [[Wave-particle duality]]
</td>
<td style="vertical-align: top;">
</td>
<td style="vertical-align: top;">
''People'':
* [[Aleksandr Grigorievich Stoletov]]
* [[Albert Einstein]]
* [[Heinrich Hertz]]
* [[Ernest Lawrence]]
* [[Robert Millikan]]
* [[Max Planck]]
* [[Joseph John Thomson]]

''Lists'':

* [[List of electronics topics]]
* [[List of optical topics]]
* [[List of physics topics]]
* [[Timeline of solar cells]]
* [[List of topics (scientific method)|Scientific method list]]
* [[Timeline of quantum mechanics, molecular physics, atomic physics, nuclear physics, and particle physics|Timeline of mechanics and physics]]
</td>
</tr>
</table>

== References ==
=== Notes ===
<references />

=== Book References ===
Serway, R. A. (1990). ''Physics for engineers and scientists'', 3rd ed. Saunders Publishing

==External links==
{{Commons|Photoelectric effect}}
* Nave, R., "''[http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html Wave-Particle Duality]''". HyperPhysics.
* Jpaul's "''[http://www.students.uiuc.edu/~jpaul/theory.htm Photovoltaics: Theory and Practice]''". [http://www.students.uiuc.edu/~jpaul/photoelectric.htm Photoelectric effect].
* "''[http://www.colorado.edu/physics/2000/quantumzone/photoelectric.html Photoelectric effect]''". Physics 2000. University of Colorado, Boulder, Colorado.
* ACEPT W3 Group, "''[http://acept.la.asu.edu/PiN/rdg/photoelectric/photoelectric.shtml The Photoelectric Effect]''". Department of Physics and Astronomy, Arizona State University, Tempe, AZ.
* Haberkern, Thomas, and N Deepak "''[http://www.faqs.org/docs/qp/ Grains of Mystique: Quantum Physics for the Layman]''". [http://www.faqs.org/docs/qp/chap03.html Einstein Demystifies Photoelectric Effect], Chapter 3.
* Department of Physics, "''[http://www.phy.davidson.edu/ModernPhysicsLabs/hovere.html The Photoelectric effect]''". Physics 320 Laboratory, Davidson College, Davidson.
* Fowler, Michael, "''[http://www.phys.virginia.edu/classes/252/photoelectric_effect.html The Photoelectric Effect]''". Physics 252, University of Virginia.
* Brandl, Michael, "[http://35.9.69.219/home/modules/pdf_modules/m213.pdf MISN-0-213 ''The Photoelectric Effect'']" ([[Portable Document Format|PDF file]]), [http://www.physnet.org Project PHYSNET].
* [http://cinarz.zdo.com/moodle/mod/resource/view.php?id=15 Quantum Chemistry I Lecture ]

''[[Applet]]s''
* Curull, Xavi Espinal, "''[http://www.ifae.es/xec/phot2.html Photoelectric effect Applet]''". ([[Java (programming language)|Java]])
* Fendt, Walter, and Taha Mzoughi, "''[http://www.walter-fendt.de/ph14e/photoeffect.htm The Photoelectric Effect]''". ([[Java (programming language)|Java]])
* "''[http://lectureonline.cl.msu.edu/~mmp/kap28/PhotoEffect/photo.htm Applet: Photo Effect]''". Open Source Distributed Learning Content Management and Assessment System. ([[Java (programming language)|Java]])

[[Category:Foundational quantum physics]]
[[Category:Electrical phenomena]]
[[Category:Albert Einstein]]

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[[tr:Fotoelektrik etki]]
[[zh:光电效应]]

Photoelectric effect

2007-01-12T11:47:35Z

JSpudeman: The introduction and history all need to be fixed up. Need to go from WHY it was important; pragmatists who use wave theory to explain it, einstein's involvement, etc. Needs to be cleaned up

[[Image:Photoelectric_effect.png|thumb|right|275px|A diagram illustrating the emission of photoelectrons from a negatively charged plate, requiring energy gained from an incoming photon to be more than the threshold frequency of the material. A positively charged plate would require a larger frequency due to attraction between the nuclei and electrons.]]
The '''photoelectric effect''' is a [[quantum mechanics|quantum]] [[electrical]] phenomenon in which, [[electron|photoelectrons]] are emitted from matter after the absorption of energy from [[electromagnetic wave|electromagnetic radiation]] such as [[x-rays]].<ref name="serway_1">''Serway, R. S.(1990), p1150''' Describes the photoelectric effect as the "Emission of photoelectrons from matter", and describes the original usage as the "Emission of Photoelectrons from metallic surfaces" after the experiments of Milikan, and others.</ref> The effect is also termed the '''Hertz Effect'''<ref>''[http://scienceworld.wolfram.com/physics/HertzEffect.html Wolfram Scienceworld]'' describes the terminology of the photoelectric effect and the previous usage of the term '''Hertz Effect'''.</ref>, due to it's discovery by [[Heinrich Rudolf Hertz]], although the term has generally fallen out of use in more current terminology. The photoelectric effect is considered to be an important step towards understanding the nature of light, due to serveral attempts to explain it using both [[wave theory|wave]] and [[particle|particulate]] theories and is thought to have influenced the formation of [[wave-particle duality]]. <ref name="serway_1" />

==Introduction==

Upon exposing a [[metal|metallic]] surface to electromagnetic radiation that is above a [[threshold]] frequency or threshold wavelength (which is specific to the type of surface and material), the photons are absorbed and [[Current (electricity)|current]] is produced. No electrons are emitted for radiation with a frequency below that of the threshold, as the electrons are unable to gain sufficient energy to overcome the electrostatic barrier presented by the termination of the crystalline surface (the material's [[work function]]). In 1905 it was known that the energy of the photoelectrons increased with increasing frequency of incident light, but the manner of the increase was not experimentally determined to be linear until 1915 when [[Robert Millikan|Robert Andrews Millikan]] showed that Einstein was correct.<ref>{{cite journal| first=Robert Andrews| last=Millikan| journal=Physical Review| volume=VII| pages=362| year=1916}}</ref>

By conservation of energy, the energy of the photon is absorbed by the electron and, if sufficient, the electron can escape from the material with a finite kinetic energy. A single photon can only eject a single electron, as the energy of one photon may only be absorbed by one electron. The electrons that are emitted are often termed '''photoelectrons'''.

The photoelectric effect helped further [[wave-particle duality]], whereby physical systems (such as [[photon]]s, in this case) display both wave-like and particle-like properties and behaviours, a concept that was used by the creators of [[quantum mechanics]]. The photoelectric effect was explained mathematically by [[Albert Einstein]], who extended the work on quanta developed by [[Max Planck]].

== Explanation ==

The photons of the light beam have a characteristic energy given by the wavelength of the light. In the photoemission process, if an electron absorbs the energy of one photon and has more energy than the [[work function]], it is ejected from the material. If the photon energy is too low, however, the electron is unable to escape the surface of the material. Increasing the intensity of the light beam does not change the energy of the constituent photons, only their number, and thus the energy of the emitted electrons does not depend on the intensity of the incoming light.

Electrons can absorb energy from photons when irradiated, but they follow an "all or nothing" principle. All of the energy from one photon must be absorbed and used to liberate one electron from atomic binding, or the energy is re-emitted. If the photon is absorbed, some of the energy is used to liberate it from the atom, and the rest contributes to the electron's kinetic (moving) energy as a free particle.

===Equations===

In analysing the photoelectric effect quantitatively using Einstein's method, the following equivalent equations are used:

Energy of [[photon]] = Energy needed to remove an [[electron]] + [[Kinetic energy]] of the emitted electron

Algebraically:
:<math>hf = \phi + E_{k_{max}} \,</math>
where
* ''h'' is [[Planck's constant]],
* ''f'' is the frequency of the incident photon,
* <math>\phi = h f_0 \ </math> is the [[work function]], or minimum energy required to remove an electron from atomic binding,
* <math>E_{k_{max}} = \frac{1}{2} m v_m^2 </math> is the maximum kinetic energy of ejected electrons,
* ''f''0 is the threshold [[frequency]] for the photoelectric effect to occur,
* ''m'' is the rest mass of the ejected electron, and
* ''<math> v_m </math>'' is the velocity of the ejected electron.

''Note'': If the photon's energy (''hf'') is not greater than the work function (<math>\phi</math>), no electron will be emitted. The work function is sometimes denoted <math>W</math>.
According to Einstein's special theory of relativity the relation between energy (E) and momentum (p) of a particle is <math>E = \sqrt{(pc)^2 + (mc^2)^2}</math>, where m is the rest mass of the particle and c is the velocity of light in a vacuum.

==History==
===Early observations===

In 1839, [[A. E. Becquerel|Alexandre Edmond Becquerel]] observed the photoelectric effect via an electrode in a conductive solution exposed to light. In [[1873]], [[Willoughby Smith]] found that [[selenium]] is photoconductive.

===Hertz's spark gaps===

[[Heinrich Hertz]], in 1887, made observations of the photoelectric effect and of the production and reception of electromagnetic (EM) waves, published in the journal [[Annalen der Physik]]. His receiver consisted of a coil with a [[spark gap]], whereupon a spark would be seen upon detection of EM waves. He placed the apparatus in a darkened box in order to see the spark better; he observed, however, that the maximum spark length was reduced when in the box. A glass panel placed between the source of EM waves and the receiver absorbed ultraviolet radiation that assisted the electrons in jumping across the gap. When removed, the spark length would increase. He observed no decrease in spark length when he substituted quartz for glass, as [[quartz]] does not absorb UV radiation.

Hertz concluded his months of investigation and reported the results obtained. He did not further pursue investigation of this effect, nor did he make any attempt at explaining how the observed phenomenon was brought about.

===JJ Thomson: electrons===

In 1899, [[Joseph John Thomson]] investigated [[ultraviolet light]] in [[Geissler tube|Crookes tube]]s. Influenced by the work of [[James Clerk Maxwell]], Thomson deduced that cathode rays consisted of negatively charged particles, later called electrons, which he called "corpuscles". In the research, Thomson enclosed a metal plate (a cathode) in a vacuum tube, and exposed it to high frequency radiation. It was thought that the oscillating electromagnetic fields caused the atoms' field to resonate and, after reaching a certain amplitude, caused a subatomic "corpuscle" to be emitted, and current to be detected. The amount of this current varied with the intensity and color of the radiation. Larger radiation intensity or frequency would produce more current.

=== Von Lenard's observations ===

In 1902, [[Philipp Eduard Anton von Lenard|Philipp von Lenard]] observed the variation in electron energy with light frequency.<ref>http://www.phys.virginia.edu/classes/252/photoelectric_effect.html</ref> He used a powerful electric arc lamp which enabled him to investigate large changes in intensity, and had sufficient power to enable him to investigate the variation of potential with light frequency. His experiment directly measured potentials, not electron kinetic energy: he found the electron energy by relating it to the maximum stopping potential (voltage) in a phototube. He found that the calculated maximum electron [[kinetic energy]] is determined by the frequency of the light. For example, an increase in frequency results in an increase in the maximum kinetic energy calculated for an electron upon liberation - [[ultraviolet radiation]] would require a higher applied stopping potential to stop current in a phototube than blue light. However Lenard's results were qualitative rather than quantitative because of the difficulty in performing the experiments: the experiments needed to be done on freshly cut metal so that the pure metal was observed, but it oxidised in a matter of minutes even in the partial vacuums he used. The current emitted by the surface was determined by the light's intensity, or brightness: doubling the intensity of the light doubled the number of electrons emitted from the surface. Lenard did not know of photons.

===Einstein: light quanta===

[[Albert Einstein]]'s mathematical description in 1905 of how it was caused by absorption of what were later called [[photon]]s, or [[quantum mechanics|quanta]] of light, in the interaction of light with the [[electron]]s in the substance, was contained in the paper named "''On a Heuristic Viewpoint Concerning the Production and Transformation of Light''". This paper proposed the simple description of "light quanta" (later called "''photons''") and showed how they could be used to explain such phenomena as the photoelectric effect. The simple explanation by Einstein in terms of absorption of single [[quanta]] of light explained the features of the phenomenon and helped explain the characteristic frequency. Einstein's explanation of the photoelectric effect won him the [[Nobel Prize]] (in Physics) of 1921.

The idea of light quanta was motivated by [[Max Planck]]'s published law of [[black-body radiation]] ("''On the Law of Distribution of Energy in the Normal Spectrum''". Annalen der Physik 4 (1901)) by assuming that Hertzian oscillators could only exist at energies E proportional to the frequency f of the oscillator by E = hf, where h is Planck's constant. Einstein, by assuming that light actually ''consisted'' of discrete energy packets, wrote an equation for the photoelectric effect that fit experiments (it explained why the energy of the photoelectrons was dependent only on the ''frequency'' of the incident light and not on its ''intensity'': a low intensity, high frequency source could supply a few high energy photons, whereas a high intensity, low frequency source would supply no photons of sufficient individual energy to dislodge any electrons). This was an enormous theoretical leap and the reality of the light quanta was strongly resisted. The idea of light quanta contradicted the wave theory of light that followed naturally from [[James Clerk Maxwell]]'s equations for electromagnetic behavior and, more generally, the assumption of [[infinite divisibility]] of energy in physical systems. Even after experiments showed that Einstein's equations for the photoelectric effect were accurate there was resistance to the idea of photons, since it appeared to contradict Maxwell's equations, which were believed to be well understood and well verified.

Einstein's work predicted that the energy of the ejected electrons would increase linearly with the frequency of the light. Perhaps surprisingly, that had not yet been tested. In 1905 it was known that the energy of the photoelectrons increased with increasing ''frequency'' of incident light -- and independent of the ''intensity'' of the light -- but the manner of the increase was not experimentally determined to be linear until 1915 when [[Robert Andrews Millikan]] showed that Einstein was correct.<ref>http://spiff.rit.edu/classes/phys314/lectures/photoe/photoe.html</ref>

=== Effect on wave-particle question ===

The photoelectric effect helped propel the then-emerging concept of the dual nature of [[light]], that light exhibits characteristics of waves and particles at different times. The effect was impossible to understand in terms of the classical [[wave]] description of light, as the energy of the emitted electrons did not depend on the intensity of the incident radiation. Classical theory predicted that the electrons could 'gather up' energy over a period of time, and then be emitted. For such a classical theory to work a pre-loaded state would need to persist in matter. The idea of the pre-loaded state was discussed in Millikan's book ''Electrons (+ & -)'' and in Compton and Allison's book ''X-Rays in Theory and Experiment''. These ideas were abandoned.

==Uses and effects==

===Photodiodes===
[[Solar cell]]s (used in [[solar power]]) and [[Photodiode|light-sensitive diodes]] use a variant of the photoelectric effect, but not ejecting electrons out of the material. In [[semiconductor]]s, light of even relatively low energy, such as visible photons, can kick electrons out of the [[valence band]] and into the higher-energy [[conduction band]], where they can be harnessed, creating [[electric current]] at a voltage related to the [[bandgap]] energy.

===Electroscopes===
[[Electroscope]]s are fork-shaped, hinged metallic leaves placed in a vacuum jar, partially exposed to the outside environment. When an electroscope is charged positively or negatively, the two leaves separate, as charge distributes evenly along the leaves causing repulsion between two like poles. When ultraviolet radiation (or any radiation above threshold frequency) shines onto the metallic outside of the electroscope, a negatively charged scope will discharge and the leaves will collapse, while nothing will happen to a positively charged scope (besides [[charge decay]]). The reason is that electrons will be liberated from the negatively charged one, gradually making it neutral, while liberating electrons from the positively charged one will make it even more positive, keeping the leaves apart

===Photoelectron spectroscopy===
Since the energy of the photoelectrons emitted is exactly the energy of the incident photon minus the material's work function or binding energy, the work function of a sample can be determined by bombarding it with a [[monochromatic]] [[X-ray]] source or [[UV]] source (typically a [[helium]] discharge lamp), and measuring the kinetic energy distribution of the electrons emitted.

This must be done in a high [[vacuum]] environment, since the electrons would be scattered by air.

A typical electron energy analyzer is a concentric hemispherical analyser (CHA), which uses an electric field to divert electrons different amounts depending on their kinetic energies. For every element and core [[atomic orbital]] there will be a different binding energy. The many electrons created from each will then show up as spikes in the analyzer, and can be used to determine the elemental composition of the sample.<ref>[http://www.chem.qmw.ac.uk/surfaces/scc/scat5_3.htm Photoelectron spectroscopy]</ref>

===Spacecraft===
The photoelectric effect will cause [[spacecraft]] exposed to sunlight to develop a positive charge. This can get up to the tens of [[volt]]s. This can be a major problem, as other parts of the spacecraft in shadow develop a negative charge (up to several kilovolts) from nearby plasma, and the imbalance can discharge through delicate electrical components. The [[static electricity|static charge]] created by the photoelectric effect is self-limiting, though, because a more highly-charged object gives up its electrons less easily.<ref>[http://www.eas.asu.edu/~holbert/eee460/spc-chrg.html Spacecraft charging]</ref>

===Moon dust===
Light from the sun hitting lunar dust causes it to become charged through the photoelectric effect. The charged dust then repels itself and lifts off the surface of the [[Moon]] by [[electrostatic levitation]]. This manifests itself almost like an "atmosphere of dust", visible as a thin haze and blurring of distant features, and visible as a dim glow after the sun has set. This was first photographed by the [[Surveyor program]] probes in the 1960s. It is thought that the smallest particles are repelled up to kilometers high, and that the particles move in "fountains" as they charge and discharge.<ref>- [http://www.firstscience.com/site/articles/moonfountains.asp Moon fountains]</ref><ref>- [http://www.spacer.com/news/dust-00a.html Dust gets a charge in a vacuum]</ref>

==See also==
<table style="text-align: left; width: 100%;" border="0" cellspacing="2"
cellpadding="2">
<tr>
<td style="vertical-align: top;">
''[[Electronics]]:''
* [[Photocurrent]]
* [[Photomultiplier]]
* [[Solar cell]]
* [[Solar power]]
* [[Transducer]]

''[[Physics]]:''
* [[Atom]]
* [[Corona discharge]]
* [[Double-slit experiment]]
* [[Electron]]
* [[Gamma ray]]
* [[Nobel Prize in Physics]]
* [[Optical phenomenon]]
* [[Planck's law of black body radiation]]
* [[Photon]]
* [[Photon dynamics in the double-slit experiment]]
* [[Photon polarization]]
* [[Quantum mechanics]]
* [[Radiant energy]]
* [[Wave-particle duality]]
</td>
<td style="vertical-align: top;">
</td>
<td style="vertical-align: top;">
''People'':
* [[Aleksandr Grigorievich Stoletov]]
* [[Albert Einstein]]
* [[Heinrich Hertz]]
* [[Ernest Lawrence]]
* [[Robert Millikan]]
* [[Max Planck]]
* [[Joseph John Thomson]]

''Lists'':

* [[List of electronics topics]]
* [[List of optical topics]]
* [[List of physics topics]]
* [[Timeline of solar cells]]
* [[List of topics (scientific method)|Scientific method list]]
* [[Timeline of quantum mechanics, molecular physics, atomic physics, nuclear physics, and particle physics|Timeline of mechanics and physics]]
</td>
</tr>
</table>

== References ==
=== Notes ===
<references />

=== Book References ===
Serway, R. A. (1990). ''Physics for engineers and scientists'', 3rd ed. Saunders Publishing

==External links==
{{Commons|Photoelectric effect}}
* Nave, R., "''[http://hyperphysics.phy-astr.gsu.edu/hbase/mod1.html Wave-Particle Duality]''". HyperPhysics.
* Jpaul's "''[http://www.students.uiuc.edu/~jpaul/theory.htm Photovoltaics: Theory and Practice]''". [http://www.students.uiuc.edu/~jpaul/photoelectric.htm Photoelectric effect].
* "''[http://www.colorado.edu/physics/2000/quantumzone/photoelectric.html Photoelectric effect]''". Physics 2000. University of Colorado, Boulder, Colorado.
* ACEPT W3 Group, "''[http://acept.la.asu.edu/PiN/rdg/photoelectric/photoelectric.shtml The Photoelectric Effect]''". Department of Physics and Astronomy, Arizona State University, Tempe, AZ.
* Haberkern, Thomas, and N Deepak "''[http://www.faqs.org/docs/qp/ Grains of Mystique: Quantum Physics for the Layman]''". [http://www.faqs.org/docs/qp/chap03.html Einstein Demystifies Photoelectric Effect], Chapter 3.
* Department of Physics, "''[http://www.phy.davidson.edu/ModernPhysicsLabs/hovere.html The Photoelectric effect]''". Physics 320 Laboratory, Davidson College, Davidson.
* Fowler, Michael, "''[http://www.phys.virginia.edu/classes/252/photoelectric_effect.html The Photoelectric Effect]''". Physics 252, University of Virginia.
* Brandl, Michael, "[http://35.9.69.219/home/modules/pdf_modules/m213.pdf MISN-0-213 ''The Photoelectric Effect'']" ([[Portable Document Format|PDF file]]), [http://www.physnet.org Project PHYSNET].
* [http://cinarz.zdo.com/moodle/mod/resource/view.php?id=15 Quantum Chemistry I Lecture ]

''[[Applet]]s''
* Curull, Xavi Espinal, "''[http://www.ifae.es/xec/phot2.html Photoelectric effect Applet]''". ([[Java (programming language)|Java]])
* Fendt, Walter, and Taha Mzoughi, "''[http://www.walter-fendt.de/ph14e/photoeffect.htm The Photoelectric Effect]''". ([[Java (programming language)|Java]])
* "''[http://lectureonline.cl.msu.edu/~mmp/kap28/PhotoEffect/photo.htm Applet: Photo Effect]''". Open Source Distributed Learning Content Management and Assessment System. ([[Java (programming language)|Java]])

[[Category:Foundational quantum physics]]
[[Category:Electrical phenomena]]
[[Category:Albert Einstein]]

[[ca:Efecte fotoelèctric]]
[[cs:Fotoelektrický jev]]
[[da:Fotoelektrisk effekt]]
[[de:Photoelektrischer Effekt]]
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[[el:Φωτοηλεκτρικό φαινόμενο]]
[[es:Efecto fotoeléctrico]]
[[eo:Fotoelektra efekto]]
[[fr:Effet photoélectrique]]
[[gl:Efecto fotoeléctrico]]
[[ko:광전 효과]]
[[id:Efek fotolistrik]]
[[it:Effetto fotoelettrico]]
[[he:האפקט הפוטואלקטרי]]
[[lt:Fotoefektas]]
[[hu:Fényelektromos jelenség]]
[[mr:प्रकाशीय विद्युत परिणाम]]
[[nl:Foto-elektrisch effect]]
[[ja:光電効果]]
[[no:Fotoelektrisk effekt]]
[[pl:Efekt fotoelektryczny]]
[[pt:Efeito fotoeléctrico]]
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[[ru:Фотоэффект]]
[[sk:Fotoelektrický jav]]
[[sl:Fotoelektrični pojav]]
[[sr:Фотоелектрични ефекат]]
[[fi:Valosähköinen ilmiö]]
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[[zh:光电效应]]

Healthy diet

2007-01-10T20:56:29Z

JSpudeman: Revert to revision 99831115 dated 2007-01-10 20:20:38 by AntiVandalBot using popups

Healthy eating is the practice of making choices about what to eat with the intent of improving or maintaining good [[health]]. Usually this involves consuming necessary [[nutrients]] by eating the appropriate amounts from all of the [[food groups]]. Since human [[nutrition]] is complex a healthy diet may vary widely subject to an individual's [[genetic]] makeup, environment, and health. For around 20% of the planet's population, lack of food and [[malnutrition]] are the main impediments to healthy eating.
 
== Nutritional Overview ==
[[Image:Colorful_Photo_of_Vegetables.png|thumb| Fresh Vegetables]]
Generally, a healthy diet will include:

1. Sufficient [[calories]] to maintain a person's metabolic and activity needs, but not so excessive as to result in [[fat]] storage greater than roughly 12% of body mass;

2. Sufficient fat, consisting mostly of mono- and polyunsaturated fats (avoiding saturated and "trans" fats) and with a balance of omega-6 and long-chain omega-3 lipids;

3. Sufficient essential [[amino acids]] ("complete protein") to provide cellular replenishment and transport proteins;

4. Essential [[micronutrients]] such as [[vitamins]] and certain minerals.

5. Avoiding directly poisonous (e.g. heavy metals) and carcinogenic (e.g. benzene) substances;

6. Avoiding foods contaminated by human pathogens (e.g. e. coli, tapeworm eggs);

7. Avoiding chronic high doses of certain foods that are benign or beneficial in small or occasional doses, such as
* foods or substances with directly toxic properties at high chronic doses (e.g. chickpeas, [[ethyl alcohol]], Vitamin A);
* foods that may interfere at high doses with other body processes (e.g. table salt);
* foods that may burden or exhaust normal functions (e.g. refined carbohydrates without adequate [[dietary fiber]]).

== Balanced Eating ==
[[Image:K3644-12.jpg|thumb|250px|Oranges can be part of a healthy diet]]
Achieving a healthy diet is popularly misperceived as being attainable by way of eating 'healthy foods'. Many people falsely believe that there are 'good' and 'bad' foods; they develop bad diets because they think that abundant eating of foods they consider 'healthy' will create a healthy diet. However, this could not be further from the truth.

The consumption of nothing but substances that are deemed healthy, such as an "all-grain diet" or a diet consisting only of [[pasta]] or other health-foods, would most likely result in deficiencies because important nutrients (like protein-based foods) would be missed. Foods such as grains, [[fish]], corn, etc. are healthy when consumed with a balanced diet, because in combination they supply us with all of the required nutrients. The most important aspect of any diet is maintaining a healthy intake and balance of foods.

The balance of micronutrients gained from meat, [[vegetables]], and other foods is what makes diets healthy, not only consuming 'healthy' foods. For instance, [[milk]], [[cheese]], and other dairy products are known to have a relatively high fat content. Removing such dairy products from a diet may lower fat ingestion, but it will also negatively affect the intake of [[calcium]] and [[riboflavin]] that such foods offer.

== Governmental Guidance ==

Although a healthy diet is based upon nutrition, people eat foods and not nutrients; as few people know which foods supply which nutrients, allowing people to self-regulate their diets means that they run the obvious risk of deficiency. Due to past difficulties of educating people about nutrient intake, governments have opted to counsel on what foods to eat rather than on what nutrients to ingest.

Most states set guidelines for a healthy diet -- these usually vary slightly from country to country based upon [[demographics]]. These guidelines do however usually share the same recommendations of eating less fried or fatty foods to reduce [[cholesterol]]. Many guidelines suggest replacing certain foods with healthier alternatives that supply an abundance of nutrients, for instance using [[legumes]] or [[beans]] within a salad or pasta.

As BMI and weight changes from person to person, the general Reference Nutrient Intakes (RNI) set by governmental institutions may be somewhat lacking for some people, despite the fact that the RNI is generally calculated as higher than the average nutrient intake. It is even thought that some people may have needs above that of the RNI, meaning even if a person achieved nutrient intake, they would still not be fulfilling the RNI. The only real way to know the RNI for a person is to implicitly monitor the intake of nutrients and amount of [[exercise]].

== Detrimental Eating Habits ==

In specific individuals, ingesting foods containing natural [[allergens]] (e.g. peanuts, shellfood) or drug-induced allergens (e.g. tyramine for a person taking an MAO inhibitor) may be life-threatening.

Some foods have low nutritional value, and if consumed on a regular basis will contribute to the decline of human health. This has been demonstrated by various epidemiological studies that have determined that foods such as processed and [[fast food|fast foods]] are linked to [[diabetes]] and various [[heart]] problems.

When improperly cut or prepared, a small number of foods (such as fugu) can result in death.

The ingredient usually cited as being most crucial to good health, [[water]], has even been known to result in death when consumed in extraordinary quantities.

== Cultural and Psychological Factors ==
[[Image:AlmondTofu.jpg|thumb|left|[[Tofu]] is considered to be a healthy food.]]
From a psychological perspective, a new healthy diet may be difficult to achieve for a person with poor eating habits. This may be due to tastes acquired in early adolescence and preferences for fatty foods. It may be easier for such a person to transition to a healthy diet if treats such as [[chocolate]] are allowed; sweets may act as mood stabilizers, which could help reinforce correct nutrient intake.

It is known that the experiences we have in childhood relating to consumption of food affect our perspective on food consumption in later life. From this, we are able to determine ourselves our limits of how much we will eat, as well as foods we will not eat - which can develop into eating disorders, such as [[anorexia]] or [[bulimia nervosa]]. This is also true with how we perceive the sizes of the meals or amounts of food we consume daily; people have different interpretations of small and large meals based on upbringing.

While plants, vegetables, and [[fruits]] are known to help reduce the incidence of chronic disease, the benefits on health posed by plant-based foods, as well as the percentage of which a diet needs to be plant based in order to have health benefits is unknown. Nevertheless, plant-based food diets in society and between nutritionist circles are linked to health and [[longevity]], as well as contributing to lowering cholesterol, weight loss, and in some cases, [[stress]] reduction.

Indeed, ideas of what counts as "healthy eating" have varied in different times and places, according to scientific advances in the field of nutrition, cultural fashions, religious proscriptions, or personal considerations.

== Public Policy Issues ==

Fears of high cholesterol were frequently voiced up until the mid-1990s. However, more recent research has shown that the distinction between high- and low-density [[lipoprotein]] ('good' and 'bad' cholesterol, respectively) must be addressed when speaking of the potential ill effects of cholesterol. Low-density lipoprotein is often prevalent in animal products, such as bacon and egg yolks, whereas high-density lipoprotein is more common in plant and fish tissues, such as [[olive oil]] and [[salmon]].

Media coverage of mass-produced, processed, "snack" or "sweet" products directly marketed at children has worked to undermine policy efforts to improve eating habits. The main problem with such advertisements for foods is that [[alcohol]] and [[fast food]] are portrayed as offering excitement, escape and instant gratification.

Particularly within the last five years government agencies have attempted to combat the amount and method of media coverage lavished upon "junk" foods. Governments also put pressure on businesses to promote healthy food options, consider limiting the availability of junk food in state-run schools, and tax foods that are high in fat. Most recently, the United Kingdom removed the rights for [[McDonalds]] to advertise its products as the majority of the foods that were seen to have low nutrient values were aimed at children under the guise of the "Happy Meal". The British Heart Foundation released its own government-funded advertisements, labeled "Food4Thought," which were targeted at children and adults displaying the gory nature of how fast food is generally constituted.

== Food Additive Controversy ==

Some people claim that food additives, such as [[artificial sweetener|artificial sweeteners]], colorants, preserving agents, and flavorings may cause health problems even though they were extensively tested before being allowed into the market. For example, artificial colorants are claimed to cause hyperactivity in susceptible children.

As another example, people on calorie-restricted diets often choose to buy products advertised as "reduced calorie" or "no sugar added". These products contain artificial sweeteners. These are safe to consume in small quantities, and are of low toxicity. Safety studies may well show some advantage in substitutions, product by product. When dieters buy reduced-calorie soft drinks, biscuits, cakes, flavored water, yogurt, and so on, all may contain combinations of the leading artificial sweeteners -- cumulative doses are at higher levels than those on which the safety studies were based.

The issue of sweetening is just one example. Other taste-enhancing additives (e.g. salt substitutes) or flavorings are also hidden in processed foods and drink, as are colorants. Mandatory food labeling is one attempt to overcome the problem. This invites the consumer to check the ingredients of their foods before consumption. However, the average person has no training in organic chemistry and its nutritional effects. Neither is it practical for individuals to manage scorecards recording all the nutrients they consume.

Some would assert that research into the toxicity of many varied artificial ingredients has been inconclusive. The USA's [[Food and Drug Administration]] has very stringent requirements for the introduction of new food ingredients, and this includes rigorous testing on animals, where the animals are given exorbitant amounts of these chemicals - far more than humans ever would be likely to consume.

== Recommendations for Young Children ==

Children thrive on routines and love to know what is expected of them. Even though every child and family is different, it is important to recognize the benefits that consistent routines provide for children. Daily routines help children learn a sense of independence, stability and value. Set times for breakfast, lunch and dinner, along with healthy snacks throughout the day to make meal times more relaxed. Most children are happier on a schedule and will become hungry at regular times.

Tips for helping make mealtime a positive experience for children:

* Allow your child to eat at his or her own pace.
* Mealtimes are opportunities for children to learn independence by making choices about food.
* Encourage your child to taste everything, but do not force him or her to eat. Because children are picky eaters by nature, it may be necessary to present them with a new food several times before they actually eat it on their own.
* Serve a variety of healthy foods (perhaps different foods on different days) so your child can get all the essential nutrients even if he or she doesn't eat some of the foods.
* If you don't have junk food in the house or don't put it on the table, your child will get hungry and eat the healthy food.
* According to JR Harris in her book "The Nurture Assumption", the best way to encourage a child to eat a food is to serve it when other children who like it are present so your child can see the other children enjoying it; seeing an adult enjoy the food has little impact.

==See also==
* [[Dietitian]]
* [[Nutrition]]
* [[Food groups]]
* [[Food guide pyramid]]
* [[Canada's Food Guide to Healthy Eating]]
* [[5 A Day]]

* [[Essential nutrient]]
* [[Dietary supplement]]s
** [[Amino acid]]s
** [[Dietary mineral|Minerals]]
** [[Nootropic]]s
** [[Nutraceutical]]s
** [[Vitamin]]s

* [[Obesity]]
** [[Childhood obesity]]
* [[Junk Food]]
* [[Fast Food]]
* [[Dieting]]

* [[List of diets|Diets (list)]]
* [[Eating]]
* [[Food]]
** [[Portal:Food|Food (portal)]]
** [[Functional food]]

* [[Health]]
** [[Portal:Health|Health (portal)]]
** [[Healthy eating pyramid]]
* [[Exercise]]
* [[Physical fitness]]
* [[Life extension]]
** [[List of life extension related topics|Life extension (topic list)]]

* [[Orthorexia nervosa]] (an obsession with healthy eating)

== References ==
#{{note|healthy_diet}} MAFF (Ministry of Agriculture, Fisheries and Food) 1990: ''Eight Guidelines for a healthy diet'' London: Food Sense
#{{note|mary_e_barasi}} Barasi, Mary E. (2003) ''Human Nutrition: A Health Perspective'' London:Arnold
#{{note|macdonalds_big_mac}} Macdonalds Corporation Quality & Nutrition information - ''McDonalds USA Big-Mac Nutrition factsheet'' Mcdonalds Corporation (http://app.mcdonalds.com/bagamcmeal?process=item&itemID=5)
#{{note|morgan_supersize}} Spurlock, M. ''Supersize Me - A film of epic Proportions'' [[Columbia Tristar]]
#{{note|plant_based_foods}} Nestle, M. (1998) ''Animal v plant foods in human diets and health'' - ''Proceedings of the Nutrition Society''
#{{note|five_a_day}} National Health Service (2005) ''Five a day - a guide to healthy eating'' NHS Press (http://www.5aday.nhs.uk/)
#{{note|american_dietary_guidelines}} Johnson, R. K. (2000). ''The 2000 Dietary Guidelines for Americans: foundation of US nutrition policy.'' - British Nutrition Foundation Nutrition Bulletin 25. p241-248
#{{note|food_pyramid}} Achterberg, C., McDonnell, E., Bagby, R. (1994) ''How to put the Food Guide Pyramid into practice - Jornal of the American Dietetic Association Volume 94'' p 1030-1035
#{{note|making_food_choices_healthier}} United Kingdom Department of Health (2005): ''Choosing Health: making healthier choices easier'' -- Public Health White Paper CM 6374 retrieved from: [http://www.dh.gov.uk/PublicationsAndStatistics/Publications/PublicationsPolicyAndGuidance/PublicationsPolicyAndGuidanceArticle/fs/en?CONTENT_ID=4094550&chk=aN5Cor United Kingdom Department of Health Website]
#{{note|pyramid_guide_agri}}United States Department of Agriculture (2005) . ''MyPyramid - Guidelines for healthy eating - Dietary guidelines for Americans'' USDA Press/Printing retrieved from [http://www.nal.usda.gov/fnic/Fpyr/pyramid.html United States Department of agriculture - MyPyramid replaces food pyramid guide]
#{{note|jamie_school}} Oliver, J., Channel Four (2005) ''Jamie's School Dinners - Documentary produced for channel four'' Television Programme.
#{{note|healthy_diet_fsa}} Food standards Authority (2005) ''8 easy steps to keeping a healthy and balanced diet - Eat well, be well'' retrieved from [http://www.eatwell.gov.uk/ Eat well, be well website.]
#{{note|five_to_nine}} National Cancer Institute (2005) ''Eat five to Nine servings of fruits and vegetables per day'' retrieved from [http://www.5aday.gov/ 5-a-day National Cancer institute]
#{{note|food_4_thought}} British Heart Foundation (2005). ''Food4Thought'' - Campaign against junk food within children's diets. retrieved from [http://www.bhf.org.uk/food4thought/index_home.asp?SecID=1742 British Heart Foundation Food4Thought]

==External links==
* [http://www.who.int/nutrition/topics/dietnutrition_and_chronicdiseases/en/ Diet, Nutrition and the prevention of chronic diseases], by a Joint [[WHO]]/[[FAO]] Expert consultation (2003)
*[http://www.greenfacts.org/en/diet-nutrition/index.htm Diet & Health] — A summary for non specialists by [[GreenFacts]] of the above WHO/FAO report.
* [http://www.publications.parliament.uk/pa/cm200102/cmselect/cmpubacc/421/42103.htm "Tackling Obesity in England"] -- U.K. Parliament report about the UK healty eating initiative.
* [http://www.nutradvice.com/healthylifestyle/ Nutradvice Healthy Lifestyle Calculator]
* Department of Health and Human Services: Centers for Disease Control and Prevention. Nutrition for everyone: Quick tips: Healthy children, healthy choices.; http://www.cdc.gov/nccdphp/dnpa/nutrition/nutrition_for_everyone/quick_tips/healthy_children.htm
*The Whole Child: For early care providers. It’s the little things: Daily Routines.; http://www.pbs.org/wholechild/providers/little.html

[[Category:Nutrition]]
[[Category:Dietetics]]

[[no:Sikringskost]]
[[pl:Dieta optymalna]]

Karl Pilkington

2007-01-10T16:32:01Z

JSpudeman: The article, unbelievably has gotten WORSE. Needs to seriously be cleaned up.

{{unreferenced|article|date=December 2006}}
{{tone}}
{{wikify}}
{{Infobox Biography
| subject_name = Karl Pilkington
| date_of_birth = [[September 23]], [[1972]]
| place_of_birth = {{flagicon|England}} [[Manchester]], [[England]].
| occupation = [[Radio Producer]], [[Performer]]
}}
'''Karl Pilkington''' (born [[September 23]], [[1972]] in [[Manchester]]) is a [[England|English]] radio producer previously best known for producing ''[[The Ricky Gervais Show]]'' on the radio station [[Xfm London|Xfm]].

After leaving Xfm, Pilkington has reached an international cult audience through his appearances with [[Ricky Gervais]] and [[Stephen Merchant]] on ''The Ricky Gervais Show'' [[podcast]]. He has made small television appearances on BBC's The Culture Show and Channel 4's 3 Minute Wonder and is also a published author.

Currently with his free time, he is focusing on his personal life and looking for new projects.

==Brief summary of Karl==

*Karl Pilkington contribution to ''The Ricky Gervais Show'' [[podcast]] consists of his unintelligent and ill-conceived view of the world coupled with a completely deadpan delivery.

*Karl Pilkington is known for his bald and "perfectly round" shaped head. In the [[podcast]]s, Ricky and Steve have urged people to put images of Karl Pilkington everywhere, aiming for Karl to be famous for his "orange"-shaped head.

*Karl Pilkington's view of life has been described by "something out of Narnia" or "a [[Roald Dahl]] book" by Gervais and Merchant especially when Karl describes his thoughts of the world or the things that have happened in his present life and the past.

*He has a big interest in people he refers to as a "[[freak]]". Gervais has said on many occasion "He (Pilkington) doesn't mean any harm, he hasn't got a malicious bone in his body". Pilkington just finds them fascinating and thinks what he would do if he was in their situation. One of his favourite "freaks" is [[Joseph Merrick]], 'The Elephant Man'. The film of Jon Merrick, ''The Elephant Man'', is one of Karl Pilkington's favourite films.

*In one of the podcast, Pilkington's remark "I could eat a knob at night" has spawned much Internet interest, as well as merchandise and music. Even [[Reuters]] took interest to Karl by publishing an article about him, which could be read everywhere in the world. The now internationally famous phrase was made during a recorded conversation about the '[[bush tucker]] trials' in the reality TV show, ''[[I'm a Celebrity, Get Me Out of Here!]]'', in which a celebrity was made to eat a kangaroo penis.

*He has kept a [[diary]] for [[2006]]. He hopes it will be a very important social document for scientists in the future to see "what was happening and that" in 2006. However, the diary consists largely of Karl's own inane experiences, such as chasing insects, going to his parents and his frequent holidays. Karl Pilkington thinks this document will have the same importance as internationally known successful diaries such as [[Anne Frank|The Diary of Anne Frank]]. Gervais, Merchant and many Pilkington fans hope that his diary will be published in [[2007]]. Karl has claimed that he might not continue his diary next year but he did see that the diary helped him being occupied with things to do. Gervais and Merchant disagreed.

*Gervais in one of the podcasts asked Pilkington which five people from the world would he take if the world was ending and had to start another civilisation on another planet but they were given a cloning machine so breeding wasn't an issue. He replied with 1. [[Patrick Moore]] to get them there to the brave new world. 2. [[Jamie Oliver]] so he can "cook us a dinner" when they've got to the new planet. Gervais questioned why wouldn't Karl just take a map and a cook book. 3. [[David Attenborough]] 4. [[Paul Danan]] so he would be the clown who nobody else liked, and distract the attention that might be focused on Karl. 5. Pilkington started to think more logically with his last answer, he thought a nurse would be a good idea. Merchant interrrupted him with the name, [[Abi Titmuss]].

==Biography==

===Disclaimer===
Bear in mind that much of the biographical information in the below sections is based on Karl's contribution on '''The Ricky Gervais Show''', so they may have valued entertainment value over strict accuracy.

=== Childhood ===

One of Pilkington's most cherished memories of his childhood was of going to bed. "I used to love goin' to bed as a kid," he has said. He can recall two instances where he laughed himself to sleep because he was so giddy and excited about bedtime. At those moments, he thought to himself, "I couldn't believe me luck".

=== Adolescence ===

Pilkington left school without collecting his exam results. According to Gervais, Pilkington attained a single "E" [[GCSE]] grade in History, which surprised him as he had no recollection of actually taking the exam. The excitement of this news was tempered somewhat by the discovery that he had not received grades for any of the GCSEs he actually does remember sitting as unfortunately he never registered for the exams, such as his Art GCSE where he recalls making a "little clay man with his arms in a car". Karl was also charged with littering crimes when he was 14 for throwing his BMX in the local river, he was released uncharged but did have to do community service looking after an elderly lady called Veria until she died.

Pilkington spent many weeks of each year living with his mother in a caravan in [[Porthmadog]], [[Wales]], missing several weeks of school as a result. His father, who worked as a taxi driver (on a four-days-on, four-days-off shift pattern) would join them when he could. Karl is surprised he's "not Welsh" given the amount of time he spent there.

Pilkington went through a number of jobs, his favourite being his paper round. Karl's school and its catchment area were near a chemical power plant. This could explain his inherent fascination with [[freak]]s ("I just like odd stuff"), as the school contained a couple of (unrelated) pupils who had "big heads", webbed hands and feet (both of whom would not befriend each other because it would be "too obvious"), together with a boy with a [[Pectus carinatum|pigeon chest]] and a boy with a father with "big eyelids". Karl left school when he was 15, and began work as a printer.

=== Adulthood ===
Pilkington was initially an off-air producer of ''The Ricky Gervais Show'', which was broadcast on [[Xfm London|Xfm]], but his antics and opinions soon led to him joining Stephen Merchant and Ricky Gervais on-air. Some of Pilkington's most popular contributions to the show include "Monkey News", a gathering of the week's news about monkeys, which is generally spurious, inaccurate and almost always about [[chimpanzee]]s; "Rockbusters", a take-off of 1980s game show [[Blockbusters (game show)|Blockbusters]], in which Karl provides 'cryptic' clues (described by Stephen Merchant as 'craptic' clues) regarding the identity of a musical group or personality for the audience to work out, which is generally hampered by the fact that the clues are near-incomprehensible and generally don't work for the answers; "Knob News", a spin off of Monkey News, with the feature containing "[[penis|knob]]-related news", such as "a man who grew a knob on his arm"; and "Karl's Diary", in which excerpts from Karl's diary are read out. His poetry has also been read on-air. Other features normally tie in with Karl's eccentric interests and theories, such as "Do We Need Them?", normally about Karl's dislike of animals deemed to be irrelevant; "Cheeky Freak of the Week", a rundown of Karl's favourite [[freak]]s; and "Songs With A Story", in which Pilkington analyses the story of a popular song, claiming that he only likes songs "with a little story goin' on and that" (such as [[Eric Clapton]]'s "[[Wonderful Tonight]]", which Karl has interpreted as about "a little fella in a wheelchair" based on what Gervais and Merchant deride as 'no evidence at all').

During his stint at Xfm, both Gervais and Merchant mocked Pilkington's professionalism, since the prizes and the quizzes themselves were poorly made, albeit because he made them during his few days present at the station, and that he took frequent holidays from work. This was also pointed out by Gervais, who claimed that Pilkington had ruined a man's career due to his laziness. Despite these criticisms, Pilkington continued to work for Xfm despite the fact he had left for a four-week hiatus.

Pilkington's baldness is a regular comic theme in his dialogues with Gervais and Merchant. He attributes this to the stress of living in London, knowing too much (Pilkington is notable for denouncing knowledge as "hassle") and putting up with Gervais' constant bullying, which involved constant berating and unstoppable head-squeezing. Gervais claims that he cannot help squeezing Pilkington's head, as it is "perfectly spherical" – however, Pilkington insists that he doesn't like having his head squeezed, or "squoze" - a word Karl believes to be real.

Aside from his apparent stressed out status, Pilkington also claims that he suffers from a bad back that – it was revealed in a recent podcast diary entry – was a consequence of trying to, as he says it, "kick me height", a phrase which he uses like a well-known expression and describes kicking his foot up until it's higher than his head, a very strange thing to do (Pilkington landed on his back, damaging it).

=== Future career ===

In December 2005, Karl left his producing job at [[Xfm]] after 10 years of service where he was head of production. Karl claimed he is considering two prospective offers of employment – a paper round and dog walking. He was formerly producer of the [[Russell Brand]] show on [[6Music]] on Sunday lunchtimes but, according to a false rumour, quit the programme 10 minutes into the second show due to some comments Russell made to him. The actual reason for Karl's departure, as confirmed by Brand's co-presenter Trevor Lock, is that 6Music's desire to release a downloadable podcast of the show conflicted with Karl's commitment to the Ricky Gervais Podcast. Karl has since appeared (via the phone) on the Russell Brand Show, talking about his holiday visit to a historic resort in Lyme Regis, Dorset and his recent viewing of ''[[Brokeback Mountain]]''.

Recently, Gervais published a book entitled ''The World of Karl Pilkington'' (ISBN 0-00-724027-9) released on [[18 September]] [[2006]]. The book comprises some of the best conversations featured in the Podcasts, as well as original ideas and drawings by Karl. Some of these can be seen on the second and sixth video podcasts. Other souvenirs that have become cult items surrounding Karl are the Karl Pilkington Head T-Shirt, due mostly to Ricky's requests in the first season of the podcasts that it would be amazing to see everyone wearing a T-Shirt with Karl's perfectly round head on it.

Karl has recently been active in the media industry, producing a number of "3 Minute Wonder" programmes for Channel 4 entitled "Some Thoughts by Karl Pilkington" and doing a voice-over for several recent [[PlayStation Portable]] television adverts in the [[UK]].

== Persona ==
It should be noted that the following is based largely on Karl Pilkington's [[persona]] as presented on the various radio shows and [[podcast]]s that he has participated in with [[Ricky Gervais]] and [[Stephen Merchant]], and that debate exists as to whether this is Pilkington's true personality, an exaggerated persona based on his own personality for comedic and entertainment effect, or even a complete fabrication.

In the radio shows and podcasts, Karl Pilkington is frequently presented as the butt of many of the jokes. He is described by Gervais and Merchant as a '[[village idiot]]', and much of the humour comes from Pilkington's lack of understanding of the world and its workings, coupled with a vague resistance to learning new information and a tendency to believe (or misinterpret) anything he reads to be fact. In the radio shows and podcasts, both Gervais and Merchant are frequently and loudly amused by Pilkington's numerous eccentricities and comical misunderstandings, whilst simultaneously being easily frustrated and quickly angered by his apparent ignorance and refusal to learn or accept any facts that contradict his own perspectives. Gervais in particular will frequently be driven to distraction and even rage by many of the points Pilkington makes in one moment, only to be reduced to helpless hysterics by another a moment later.

Pilkington is notable for developing theories and telling stories (particularly in his famed 'Monkey News' segments) that are highly exaggerated, surreal and involving events and issues which he has clearly misunderstood and misinterpreted but which he nonetheless appears to believe with absolute certainty to be the truth. These stories frequently involve events that are physically impossible, or at least highly unlikely (such as [[monkey]]s piloting [[spacecraft]] equipped with [[banana]] dispensers) and frequently become completely nonsensical due to Pilkington's own misunderstandings and misinterpretations, coupled with his tendency to make large, unexplained leaps of faith and logic in the process (such as granting animals qualities of intelligence, social interaction and purpose that they do not in fact possess). He also has a tendency within these stories to neglect to provide important dates and details, and instead to substitute them with vague and unhelpful phrases (such as "In the olden days, right, there was a short hairy fella..."), which frequently makes his reliability questionable at best; his refusal (and apparent disdain for) providing concrete - or even accurate - facts and interpretations frequently lead Gervais and Merchant to accuse him of collecting all his information on any chosen subject merely by reading a headline or a dubious piece of information on the Internet and then constructing a story about it in his head.

In keeping with his quotation that "knowledge is almost annoying", Pilkington frequently bemoans various discoveries and facts that he learns (usually from Gervais and Merchant) as being pointless and of limited value, being used only to complicate life. He is frequently dismissive of (or even resistant to or annoyed by) the various facts and information with which he is provided, and appears to advocate limiting knowledge and personal discovery as much as possible. However, he frequently bases his conclusions on a misunderstood, over-simplistic, or even entirely inaccurate perspective on what he is talking about. When provided with a fact or a question, Pilkington will frequently misinterpret what he is being told or asked. This results in an inaccurate translation of what he is being told or a complete tangent from the point that actually is being made. Gervais in particular often attributes this to what he calls Pilkington's mental "filter", describing it as a process in which Pilkington receives sensible, accurate information and mentally translates it into what Gervais and Merchant frequently describe as "absolute twaddle" (jokingly describing it as sounding like a "discordant [[piano]]" or "Those [[Czechoslovakia|Czech]] cartoons from 1963 with people hitting [[wok]]s for sound effects").

Many of Pilkington's anecdotes revolve around his family, and present a highly eccentric portrayal of his upbringing and the relatives who are depicted. Frequently mentioned is his girlfriend, Suzanne, who is frequently portrayed within these stories as reacting in a somewhat long-suffering fashion to Karl's eccentricities and his idiosyncratic viewpoint of the world and how it works.

=== Fictional character? ===
Although Merchant and Gervais publicly maintain that the personality he displays in the podcasts is genuinely that of Karl Pilkington, speculation has arisen that Pilkington is a fictional persona created and scripted by the two. In particular, Chris Campling, a journalist writing for the ''[[The Times]]'', has speculated that Karl Pilkington is not a real person, but an actor portraying the role of a scripted character created by Ricky Gervais and Stephen Merchant<ref>Chris Campling, 2005. "[http://entertainment.timesonline.co.uk/article/0,,14934-1653726,00.html A qualified success]." ''[[The Times]]''.</ref>. Campling pointed towards the fact that Pilkington's views on Chinese people had been stated on Gervais' radio show, before he stated the same thing on his interview with Gervais, on the ''Politics'' DVD. Other examples of apparently recycled material or inconsistencies can be found within the radio shows and podcasts, such as a segment wherein Pilkington discussed his boredom during a stay in an [[Edinburgh]] hotel room on the Xfm show, only to later professing in a podcast that he hasn't "even been to [[Scotland]] yet".

On [[April 24]], [[2006]], ''[[The New York Times]]'' ran an article about Ricky Gervais and the podcast which described Pilkington's behaviour as a well executed "[[deadpan]] comedian" routine which "crosses [[Ali G]] and [[Steven Wright]]".<ref>[http://www.nytimes.com/2006/04/24/arts/television/24heff.html "A Comic Expands His Persona via Podcast on 'The Ricky Gervais Show']," Virginia Heffernan, ''The New York Times'', April 24, 2006</ref>

Merchant and Gervais themselves have repeatedly denied claims that Pilkington is a creation of theirs. In an on-air response to Campling's claims during a broadcast on [[Xfm]], Merchant stated that he would be "ashamed" if the radio show was scripted, adding that "If we came up with a character as good as Karl, we would never use him on a poxy little radio station like this one ([[Xfm London]])" <ref>[http://www.xfm.co.uk/Article.asp?id=95643, 'The Ricky Gervais Show, Episode Four', broadcast Xfm June 2005)</ref> Gervais concurred, pointing out that writing half-hour episodes of shows such as ''The Office'' and ''Extras'' took the two up to a year, thus making the writing of two-hour radio shows impractical.

== Celebrity ==
[[Image:Pilkington_stencil_2.jpg|thumb|330px|A stencil in [[Augusta, Georgia]], of Karl Pilkington and his famous soundbite "I could eat a knob at night".]]
As a result of the success of ''The Ricky Gervais Show'' podcasts in particular, Pilkington has become something of a cult celebrity. Pilkington is sometimes mentioned in interviews that Gervais gives, and is often on the receiving end of Gervais's practical jokes. When asked who was the funniest person he knew, Gervais said Karl Pilkington, whom he mentioned was "the funniest man alive in Britain today." In addition, Pilkington appears in a twenty minute interview on Ricky Gervais's live stand-up comedy DVD, ''Politics.''

Karl recently reached new heights of fame by commenting that he could "eat a knob at night" during a discussion on the podcast about ''[[I'm a Celebrity, Get Me Out of Here!]],'' a British reality TV show in which contestants had to eat a [[kangaroo]]'s [[penis]]. Karl stated that, whilst in the morning he would be unable to face the appendage due to having a weak [[stomach]], he would more than likely be able to stomach it in the evening. His phrase "I could eat a knob at night" has since spawned [[dance music]] remixes, [[T-shirt]]s and other merchandise, as well as discussion on many websites and thousands of [[search engine]] hits.

==Notes==
<div class="references-small">
<references/>
</div>

==External links==
{{wikiquote}}
'''News'''
*[http://www.rickygervais.com Ricky Gervais's official site with news about Karl Pilkington's activities]
'''Audio'''
*[http://www.xfm.co.uk/article.asp?id=3673 Xfm - Ricky Gervais Show clip archive]
*[http://www.gervaisworld.com/ricky-gervais-xfm.html ''XFM''] for download at Gervaisworld
'''Fan Sites'''
*[http://www.pilkipedia.co.uk Pilkipedia (declared as Gervais' favourite website)] (http://www.guardian.co.uk/theguide/features/story/0,,1852500,00.html)
*[http://www.thespringcolds.com/globalvillageidiot/ Karl Pilkington: Global Village Idiot]
*[http://www.karl-pilkington.com/ Karl Pilkington fansite, www.karl-pilkington.com]
*[http://www.richard.hare.dsl.pipex.com/rgervais.html Site detailing songs played and discussion of shows on Xfm going back to 2001]
*[http://xfm.co.uk/Article.asp?id=86779 Xfm profile]
*[http://www.stinkywinkles.com "Animations from the podcast and associated works"]
*[http://www.gervaisworld.com ''Karl Pilkington'' Videos, audio and more] at Gervaisworld
'''Video'''
*[http://www.gervaisworld.com ''Karl Pilkington'' Videos] at Gervaisworld
*[http://www.amazon.co.uk/World-Karl-Pilkington/dp/0007240279/sr=8-1/qid=1165748554/ref=pd_ka_1/203-9609989-9040730?ie=UTF8&s=books Karl strives to find a copy of his book, and some shameless advertising from Ricky Gervais]
'''Articles'''
*[http://www.drquincy.com/personal/nonfiction/humour/karlpilkingtonthefunniestmanintheworld/ Karl Pilkington, the Funniest Man in the World?]
*[http://www.spectator.co.uk/the-magazine/features/26430/meet-the-funniest-man-on-the-planet.thtml Interview in The Spectator]
*[http://www.gervaisworld.com ''Karl Pilkington'' Bio] at Gervaisworld

[[Category:British radio personalities|Pilkington, Karl]]
[[Category:Podcasters|Pilkington, Karl]]
[[Category:People from Manchester|Pilkington, Karl]]

Wikipedia:WikiProject Medicine

2007-01-09T23:01:07Z

JSpudeman: I've added the IRC channel -- if you want to chat on collaborations and article issues, just pop in.

{{dablink|'''"[[WP:MED]]"''' redirects here. For the [[Wikipedia:Mediation Committee]], see [[WP:MC]] or [[WP:MEDCOM]].}}
{{shortcut|[[WP:MED]]}}
Welcome to the '''WikiProject Medicine'''. The purpose of this project is to help editors assess and prioritize medical articles on Wikipedia. [[:Category:Medicine]] is a broad field; while there are always articles that need improvement, there are some for which it is especially important to write a high-quality article. Both preclinical and clinical topics are welcome here. Feel free to add your assessment of unrated articles, and to update the status of articles that have improved (or degenerated). You may even create your own list, although it's probably best to bring it up on the [[Wikipedia talk:WikiProject Medicine|talk page]]. Thanks to [[Wikipedia:WikiProject Chemicals|WikiProject Chemicals]] and [[Wikipedia:WikiProject Anti-war|WikiProject Anti-war]] for inspiration.

This project aims to assist with prioritization and collaboration (it also hosts the [[WP:MCOTW|Medicine Collaboration of the Week]]). It is the "parent" of two WikiProjects, [[Wikipedia:WikiProject Clinical medicine|WikiProject Clinical medicine]] and [[Wikipedia:WikiProject Preclinical Medicine|WikiProject Preclinical Medicine]]. Guidelines for and discussions of relevant articles can be found at those projects, and at the [irc://irc.freenode.net/##medicine IRC Channel]


{| cellpadding=3 cellspacing=0 width=550 border=1 style="border-collapse:collapse" align="center"
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{| cellpadding=3 cellspacing=0 width=550 border=1 style="border-collapse:collapse" align="center"
|bgcolor="#99ccff"| <center>'''[[Wikipedia:WikiProject Clinical medicine|WikiProject Clinical medicine]]'''</center>
|bgcolor="#99ccff"| <center>'''[[Wikipedia:WikiProject Preclinical Medicine|WikiProject Preclinical Medicine]]'''</center>
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|bgcolor="#99ccff"| <center>'''[[Portal:Medicine/WikiProjects|WikiProjects related to medicine]]'''</center>
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==News, announcements==
{{CurrentMCOTW}} 
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{{MedProjectNews}}

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If you have a job for the project, please list it here:

{| cellpadding=3 cellspacing=0 border=1 style="border-collapse:collapse"
|bgcolor="#ffe4b5"| '''Editor'''
|bgcolor="#ffe4b5"| <center>'''Article'''
|bgcolor="#ffe4b5"| <center>'''Comment'''</center>
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| I took this page from a stub to something with at least some information, however a lot of work needs to be done. Any help would be much appreciated. {{User:je_at_uwo/sig}} 06:12, 16 November 2006 (UTC)
|-
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| This article needs more work, and currently has a riduculous bit on a cyclopic kitten, which managed to express amazement at what is a defect possible in all mammals.[[User:213.48.73.94|213.48.73.94]] 12:55, 21 November 2006 (UTC)
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| [[Depleted uranium]], [[Gulf War syndrome]], [[Uranium trioxide]], [[Uranium]]
| Pro-military types constantly censor these articles, and fight with those who try to expand them. [[Talk:Depleted uranium#Comparison of the two versions]] contains a comparison of the current version of [[Depleted uranium]] with a recent major revision which replaced a lot of what some people had been taking out of it over the past several months. Please keep an eye on them and be bold in reverting the military censors.
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|Recent edit makes some rather specific claims of medical technology (skin grafts, vaccination) that, if accurate, should be expanded upon and, if not, should be removed.
|}

[[Category:WikiProject Biology|Medicine]]
[[Category:WikiProject Medicine| ]]
[[Category:WikiProjects participating in Wikipedia 1.0 assessments|{{PAGENAME}}]]

Talk:Snell's law

2007-01-07T23:55:05Z

JSpudeman: Fixup

{{physics|class=B|importance=High}}
It would be nice to spell Snel's name correctly (i.e., with a single "l").
His name is "Snel" in his native language, or "Snellius" in Latin. The common spelling "Snell" is a solecism committed by people who know neither Dutch nor Latin.

Perhaps it would also be wise to point out that Snel was not the *original* discoverer; the law was first found by Thomas Harriot, about 1600 -- two decades before Snel's work.

I have some information about this at

http://mintaka.sdsu.edu/GF/explain/optics/discovery.html

----

An experimental paragraph added. See a short article by Kwan, Dudley and Lantz about this in Physics World in 2003 or 2002. This article says that Thomas Harriot (Hariot may be his preferred spelling) was actually not the first.
*I've improved the history section with information from that article, and incorporated the references in it. Hope that's clearer. I'm not sure what to do with the external link, which contradicts those articles (says Harriot was first). -- [[User:DrBob|Bob Mellish]] 17:36, 30 September 2005 (UTC)

Snell may be a solecism, but it's English, and it's the English name of the law, even if not how the man wrote his own name. Given how fluid spelling could be in the 17th century, it could be that Snell spelt his name in several different ways. Can someone check this?

== Image wrong? ==

The image shows that the normal is the boundary between the media, rather than being horizontal to the boundary. Also, <math>\theta_1</math> and <math>\theta_2</math> are wrongly labelled as a result. The image disagrees with the text. See ScienceWorld [http://scienceworld.wolfram.com/physics/SnellsLaw.html] for how the image should be corrected.

The image is misleading and confusing, and should be rectified as soon as possible; however, as I lack experience with graphics, I request someone to upload a corrected version as soon as possible.

*Um, no. The image is correct, and correctly labelled. The image in the article has the two media on the left and right sides of the diagram; the interface runs vertically. The image at Scienceworld has the two media at the top and bottom of their diagram; their interface runs horizontally. Try rotating one of the diagrams by 90°, and you'll see how they match. -- [[User:DrBob|Bob Mellish]] 18:25, 26 September 2005 (UTC)

== Snel's law spelling ==

I agree it is Snel and not Snell's law. Also in English. The 'discoverer' (not getting in the historical issue here, just the spelling bit) of the quantitative law of refraction was 'Willebrord Snel van Royen', thus one l, and there is no fluidity to this spelling as far as I know. The two-l-spelling has nothing to do with 'Snel' spelled differently in the English language but with incorrect de-latinazation of Snellius.

== Other formulae ==

I've seen this formula used quite a lot in some establishments as an expansion of the original law for wavelength... 

<math>\frac {\lambda_0}{\lambda_1} = \frac{v_o}{v_m} = \frac{c / n_1}{c / n_2} = \frac{n_2}{n_1}</math> to...
<math>\lambda_1 sin\theta_1 = \lambda_2 sin\theta_2</math> 

[[User:JSpudeman|James S]] 00:12, 11 December 2006 (UTC)

:Those ratios of velocities, wavelengths, indices of refraction, etc. are fine, but they are not Snell's law. Snell's law needs to have the sines of the angles in it. We seem to have forgotten to state the law near the top of the article anywhere. I'm working on it... [[User:Dicklyon|Dicklyon]] 20:04, 22 December 2006 (UTC)
:OK, I fixed the lead, putting the law equation and illustration into it; and I added a book page of history. I don't really understand the point of what someone was trying to do with these relations in the Explanation section, so I'll leave it for now. But as I said, without the angles, or some measurement proportional to their sines, it's not Snell's law. [[User:Dicklyon|Dicklyon]] 20:40, 22 December 2006 (UTC)

==Merge from Angle of refraction?==

I propose to merge [[Angle of refraction]] into Snell's law, since it covers exactly the same material. Please support, oppose, or otherwise comment here. [[User:Dicklyon|Dicklyon]] 08:36, 23 December 2006 (UTC)
:'''support''' [[User:The Photon|The Photon]] 03:46, 24 December 2006 (UTC)
:Expecting no objection, I went ahead and incorporated a few bits from there that we didn't have here, and converted it to a redirect. [[User:Dicklyon|Dicklyon]] 05:30, 24 December 2006 (UTC)

==Reverting JCraw's extensive uncommented changes==

JCRaw, that's a lot of changes to do all at once without even any change comments. You've de-linked the references from what they refer to, and made them into a very hard-to-maintain form (because the numbers don't track automatically). And you've introduced non-words (e.g. ''constance'') and grammatical errors into the lead. I haven't reviewed most of the changes yet, but on these bases alone I'm going to revert, and we can make the changes you want more slowly and carefully, giving other editors a chance to collaborate on them, please. [[User:Dicklyon|Dicklyon]] 17:00, 4 January 2007 (UTC)

JSpudeman, the way you've put it back is really no better. You still have the hard-to-maintain ref style, grammatical errors in the lead, and unclear what point you're trying to make there. The statement about "it's [sic] original form" is probably wrong, since the constant ratio of sines was articulated before velocities or indices of refraction were known. [[User:Dicklyon|Dicklyon]] 23:24, 4 January 2007 (UTC)

Point noted; i know of the application Fermat's principle to Snell's Law, but i was unaware of the history linking them together. However -- what was the original formula that was used before the inclusion of least-time? It would be interesting to know how the original formula was developed. On that note, do you own that book? I presume that from your reference to it's contents that you do? If so, why not reference it? [[User:JSpudeman|James S]] 23:23, 7 January 2007 (UTC)

As a slight offshoot to the topic here, perhaps the introduction should be more explanatory:

:''In optics and physics, Snell's law (also known as Descartes' Law or the law of refraction) is a formula that relates the angles where a ray of light crosses a boundary between different media, such as air and glass.''

Although it's fine, it doesn't quite explain the reason for the relation of the angles, or what is being related other than "angles" (i.e incidence/refraction).

Similarly, i was just taking a glance at the [http://en.wikipedia.org/w/index.php?title=Snell%27s_law&diff=96133490&oldid=95512206 edit history] and noticed that apart from a slight change in grammar, some of the explanations were removed. Again, i'm staying well away from this one, but i'm wondering why that is exactly. Although practically the same information is there, it makes it more difficult for those who are reading the article as an impartial/non-informed user, i think, to [[Wikipedia:Manual_of_Style#Big.2C_little.2C_long.2C_short|pick up on the article]].

I'll leave it in your hands, as my edits would undoubtedly be reverted ;-) [[User:JSpudeman|James S]] 23:36, 7 January 2007 (UTC)

==The original form of the law==

Here's [http://books.google.com/books?vid=OCLC13466184&id=ZwIAAAAAQAAJ&pg=RA4-PA295&lpg=RA4-PA295&dq=snell+sines+ratio+date:0-1820#PRA4-PA295,M1 an 1803 book] that explains that Snel did the same thing that [[Ibn Sahl]] had done. Nowhere does the velocity of propagation or the index of refraction enter into his observation that the ratio of sines is a constant for a given pair of media. Later, when it was realized that light speed varies in different media, it was realized that the law of sines was in agreement with a principle of least time, or [[Fermat's principle]]; that's where velocity and index started to come into the equation, via their ratio. Let's not get the cart before the horse on this. [[User:Dicklyon|Dicklyon]] 01:42, 5 January 2007 (UTC)

Talk:Snell's law

2007-01-07T23:53:54Z

JSpudeman: Don't worry, i'm maintaining good faith, just keeping the hell away :-)

{{physics|class=B|importance=High}}
It would be nice to spell Snel's name correctly (i.e., with a single "l").
His name is "Snel" in his native language, or "Snellius" in Latin. The common spelling "Snell" is a solecism committed by people who know neither Dutch nor Latin.

Perhaps it would also be wise to point out that Snel was not the *original* discoverer; the law was first found by Thomas Harriot, about 1600 -- two decades before Snel's work.

I have some information about this at

http://mintaka.sdsu.edu/GF/explain/optics/discovery.html

----

An experimental paragraph added. See a short article by Kwan, Dudley and Lantz about this in Physics World in 2003 or 2002. This article says that Thomas Harriot (Hariot may be his preferred spelling) was actually not the first.
*I've improved the history section with information from that article, and incorporated the references in it. Hope that's clearer. I'm not sure what to do with the external link, which contradicts those articles (says Harriot was first). -- [[User:DrBob|Bob Mellish]] 17:36, 30 September 2005 (UTC)

Snell may be a solecism, but it's English, and it's the English name of the law, even if not how the man wrote his own name. Given how fluid spelling could be in the 17th century, it could be that Snell spelt his name in several different ways. Can someone check this?

== Image wrong? ==

The image shows that the normal is the boundary between the media, rather than being horizontal to the boundary. Also, <math>\theta_1</math> and <math>\theta_2</math> are wrongly labelled as a result. The image disagrees with the text. See ScienceWorld [http://scienceworld.wolfram.com/physics/SnellsLaw.html] for how the image should be corrected.

The image is misleading and confusing, and should be rectified as soon as possible; however, as I lack experience with graphics, I request someone to upload a corrected version as soon as possible.

*Um, no. The image is correct, and correctly labelled. The image in the article has the two media on the left and right sides of the diagram; the interface runs vertically. The image at Scienceworld has the two media at the top and bottom of their diagram; their interface runs horizontally. Try rotating one of the diagrams by 90°, and you'll see how they match. -- [[User:DrBob|Bob Mellish]] 18:25, 26 September 2005 (UTC)

== Snel's law spelling ==

I agree it is Snel and not Snell's law. Also in English. The 'discoverer' (not getting in the historical issue here, just the spelling bit) of the quantitative law of refraction was 'Willebrord Snel van Royen', thus one l, and there is no fluidity to this spelling as far as I know. The two-l-spelling has nothing to do with 'Snel' spelled differently in the English language but with incorrect de-latinazation of Snellius.

== Other formulae ==

I've seen this formula used quite a lot in some establishments as an expansion of the original law for wavelength... 

<math>\frac {\lambda_0}{\lambda_1} = \frac{v_o}{v_m} = \frac{c / n_1}{c / n_2} = \frac{n_2}{n_1}</math> to...
<math>\lambda_1 sin\theta_1 = \lambda_2 sin\theta_2</math> 

[[User:JSpudeman|James S]] 00:12, 11 December 2006 (UTC)

:Those ratios of velocities, wavelengths, indices of refraction, etc. are fine, but they are not Snell's law. Snell's law needs to have the sines of the angles in it. We seem to have forgotten to state the law near the top of the article anywhere. I'm working on it... [[User:Dicklyon|Dicklyon]] 20:04, 22 December 2006 (UTC)
:OK, I fixed the lead, putting the law equation and illustration into it; and I added a book page of history. I don't really understand the point of what someone was trying to do with these relations in the Explanation section, so I'll leave it for now. But as I said, without the angles, or some measurement proportional to their sines, it's not Snell's law. [[User:Dicklyon|Dicklyon]] 20:40, 22 December 2006 (UTC)

==Merge from Angle of refraction?==

I propose to merge [[Angle of refraction]] into Snell's law, since it covers exactly the same material. Please support, oppose, or otherwise comment here. [[User:Dicklyon|Dicklyon]] 08:36, 23 December 2006 (UTC)
:'''support''' [[User:The Photon|The Photon]] 03:46, 24 December 2006 (UTC)
:Expecting no objection, I went ahead and incorporated a few bits from there that we didn't have here, and converted it to a redirect. [[User:Dicklyon|Dicklyon]] 05:30, 24 December 2006 (UTC)

==Reverting JCraw's extensive uncommented changes==

JCRaw, that's a lot of changes to do all at once without even any change comments. You've de-linked the references from what they refer to, and made them into a very hard-to-maintain form (because the numbers don't track automatically). And you've introduced non-words (e.g. ''constance'') and grammatical errors into the lead. I haven't reviewed most of the changes yet, but on these bases alone I'm going to revert, and we can make the changes you want more slowly and carefully, giving other editors a chance to collaborate on them, please. [[User:Dicklyon|Dicklyon]] 17:00, 4 January 2007 (UTC)

JSpudeman, the way you've put it back is really no better. You still have the hard-to-maintain ref style, grammatical errors in the lead, and unclear what point you're trying to make there. The statement about "it's [sic] original form" is probably wrong, since the constant ratio of sines was articulated before velocities or indices of refraction were known. [[User:Dicklyon|Dicklyon]] 23:24, 4 January 2007 (UTC)

Point noted; i know of the application Fermat's principle to Snell's Law, but i was unaware of the history linking them together. However -- what was the original formula that was used before the inclusion of least-time? It would be interesting to know how the original formula was developed. On that note, do you own that book? I presume that from your reference to it's contents that you do? If so, why not reference it? [[User:JSpudeman|James S]] 23:23, 7 January 2007 (UTC)

As a slight offshoot to the topic here, perhaps the introduction should be more explanatory:

:''In optics and physics, Snell's law (also known as Descartes' Law or the law of refraction) is a formula that relates the angles where a ray of light crosses a boundary between different media, such as air and glass.''

Although it's fine, it doesn't quite explain the reason for the relation of the angles, or what is being related other than "angles" (i.e incidence/refraction).

Similarly, i was just taking a glance at the [http://en.wikipedia.org/w/index.php?title=Snell%27s_law&diff=96133490&oldid=95512206 edit history] and noticed that apart from a slight change in grammar, some of the explanations were removed. Again, i'm staying well away from this one, but i'm wondering why that is exactly. Although practically the same information is there, it makes it more difficult for those who are reading the article as an impartial/non-informed user, i think, to [[[[Wikipedia:Manual_of_Style#Big.2C_little.2C_long.2C_short|pick up on the article]].

I'll leave it in your hands, as my edits would undoubtedly be reverted ;-) [[User:JSpudeman|James S]] 23:36, 7 January 2007 (UTC)

==The original form of the law==

Here's [http://books.google.com/books?vid=OCLC13466184&id=ZwIAAAAAQAAJ&pg=RA4-PA295&lpg=RA4-PA295&dq=snell+sines+ratio+date:0-1820#PRA4-PA295,M1 an 1803 book] that explains that Snel did the same thing that [[Ibn Sahl]] had done. Nowhere does the velocity of propagation or the index of refraction enter into his observation that the ratio of sines is a constant for a given pair of media. Later, when it was realized that light speed varies in different media, it was realized that the law of sines was in agreement with a principle of least time, or [[Fermat's principle]]; that's where velocity and index started to come into the equation, via their ratio. Let's not get the cart before the horse on this. [[User:Dicklyon|Dicklyon]] 01:42, 5 January 2007 (UTC)

Talk:Snell's law

2007-01-07T23:36:04Z

JSpudeman: I've been criticised for my grammar, so it's only fair i make a rebutle. Also, the references were fine, but i'm still unclear what you mean by "easy to edit" ref style.

{{physics|class=B|importance=High}}
It would be nice to spell Snel's name correctly (i.e., with a single "l").
His name is "Snel" in his native language, or "Snellius" in Latin. The common spelling "Snell" is a solecism committed by people who know neither Dutch nor Latin.

Perhaps it would also be wise to point out that Snel was not the *original* discoverer; the law was first found by Thomas Harriot, about 1600 -- two decades before Snel's work.

I have some information about this at

http://mintaka.sdsu.edu/GF/explain/optics/discovery.html

----

An experimental paragraph added. See a short article by Kwan, Dudley and Lantz about this in Physics World in 2003 or 2002. This article says that Thomas Harriot (Hariot may be his preferred spelling) was actually not the first.
*I've improved the history section with information from that article, and incorporated the references in it. Hope that's clearer. I'm not sure what to do with the external link, which contradicts those articles (says Harriot was first). -- [[User:DrBob|Bob Mellish]] 17:36, 30 September 2005 (UTC)

Snell may be a solecism, but it's English, and it's the English name of the law, even if not how the man wrote his own name. Given how fluid spelling could be in the 17th century, it could be that Snell spelt his name in several different ways. Can someone check this?

== Image wrong? ==

The image shows that the normal is the boundary between the media, rather than being horizontal to the boundary. Also, <math>\theta_1</math> and <math>\theta_2</math> are wrongly labelled as a result. The image disagrees with the text. See ScienceWorld [http://scienceworld.wolfram.com/physics/SnellsLaw.html] for how the image should be corrected.

The image is misleading and confusing, and should be rectified as soon as possible; however, as I lack experience with graphics, I request someone to upload a corrected version as soon as possible.

*Um, no. The image is correct, and correctly labelled. The image in the article has the two media on the left and right sides of the diagram; the interface runs vertically. The image at Scienceworld has the two media at the top and bottom of their diagram; their interface runs horizontally. Try rotating one of the diagrams by 90°, and you'll see how they match. -- [[User:DrBob|Bob Mellish]] 18:25, 26 September 2005 (UTC)

== Snel's law spelling ==

I agree it is Snel and not Snell's law. Also in English. The 'discoverer' (not getting in the historical issue here, just the spelling bit) of the quantitative law of refraction was 'Willebrord Snel van Royen', thus one l, and there is no fluidity to this spelling as far as I know. The two-l-spelling has nothing to do with 'Snel' spelled differently in the English language but with incorrect de-latinazation of Snellius.

== Other formulae ==

I've seen this formula used quite a lot in some establishments as an expansion of the original law for wavelength... 

<math>\frac {\lambda_0}{\lambda_1} = \frac{v_o}{v_m} = \frac{c / n_1}{c / n_2} = \frac{n_2}{n_1}</math> to...
<math>\lambda_1 sin\theta_1 = \lambda_2 sin\theta_2</math> 

[[User:JSpudeman|James S]] 00:12, 11 December 2006 (UTC)

:Those ratios of velocities, wavelengths, indices of refraction, etc. are fine, but they are not Snell's law. Snell's law needs to have the sines of the angles in it. We seem to have forgotten to state the law near the top of the article anywhere. I'm working on it... [[User:Dicklyon|Dicklyon]] 20:04, 22 December 2006 (UTC)
:OK, I fixed the lead, putting the law equation and illustration into it; and I added a book page of history. I don't really understand the point of what someone was trying to do with these relations in the Explanation section, so I'll leave it for now. But as I said, without the angles, or some measurement proportional to their sines, it's not Snell's law. [[User:Dicklyon|Dicklyon]] 20:40, 22 December 2006 (UTC)

==Merge from Angle of refraction?==

I propose to merge [[Angle of refraction]] into Snell's law, since it covers exactly the same material. Please support, oppose, or otherwise comment here. [[User:Dicklyon|Dicklyon]] 08:36, 23 December 2006 (UTC)
:'''support''' [[User:The Photon|The Photon]] 03:46, 24 December 2006 (UTC)
:Expecting no objection, I went ahead and incorporated a few bits from there that we didn't have here, and converted it to a redirect. [[User:Dicklyon|Dicklyon]] 05:30, 24 December 2006 (UTC)

==Reverting JCraw's extensive uncommented changes==

JCRaw, that's a lot of changes to do all at once without even any change comments. You've de-linked the references from what they refer to, and made them into a very hard-to-maintain form (because the numbers don't track automatically). And you've introduced non-words (e.g. ''constance'') and grammatical errors into the lead. I haven't reviewed most of the changes yet, but on these bases alone I'm going to revert, and we can make the changes you want more slowly and carefully, giving other editors a chance to collaboration on them, please. [[User:Dicklyon|Dicklyon]] 17:00, 4 January 2007 (UTC)

JSpudeman, the way you've put it back is really no better. You still have the hard-to-maintain ref style, grammatical errors in the lead, and unclear what point you're trying to make there. The statement about "it's [sic] original form" is probably wrong, since the constant ratio of sines was articulated before velocities or indices of refraction were known. [[User:Dicklyon|Dicklyon]] 23:24, 4 January 2007 (UTC)

Point noted; i know of the application Fermat's principle to Snell's Law, but i was unaware of the history linking them together. However -- what was the original formula that was used before the inclusion of least-time? It would be interesting to know how the original formula was developed. On that note, do you own that book? I presume that from your reference to it's contents that you do? If so, why not reference it? [[User:JSpudeman|James S]] 23:23, 7 January 2007 (UTC)

As a slight offshoot to the topic here, perhaps the introduction should be more explanatory:

:''In optics and physics, Snell's law (also known as Descartes' Law or the law of refraction) is a formula that relates the angles where a ray of light crosses a boundary between different media, such as air and glass.''

Although it's fine, it doesn't quite explain the reason for the relation of the angles, or what is being related other than "angles" (i.e incidence/refraction). I'll leave it in your hands, as my edits would undoubtedly be reverted ;-) [[User:JSpudeman|James S]] 23:36, 7 January 2007 (UTC)

==The original form of the law==

Here's [http://books.google.com/books?vid=OCLC13466184&id=ZwIAAAAAQAAJ&pg=RA4-PA295&lpg=RA4-PA295&dq=snell+sines+ratio+date:0-1820#PRA4-PA295,M1 an 1803 book] that explains that Snel did the same thing that [[Ibn Sahl]] had done. Nowhere does the velocity of propagation or the index of refraction enter into his observation that the ratio of sines is a constant for a given pair of media. Later, when it was realized that light speed varies in different media, it was realized that the law of sines was in agreement with a principle of least time, or [[Fermat's principle]]; that's where velocity and index started to come into the equation, via their ratio. Let's not get the cart before the horse on this. [[User:Dicklyon|Dicklyon]] 01:42, 5 January 2007 (UTC)

Talk:Snell's law

2007-01-07T23:23:50Z

JSpudeman: Fixed up your over-caps :-P

{{physics|class=B|importance=High}}
It would be nice to spell Snel's name correctly (i.e., with a single "l").
His name is "Snel" in his native language, or "Snellius" in Latin. The common spelling "Snell" is a solecism committed by people who know neither Dutch nor Latin.

Perhaps it would also be wise to point out that Snel was not the *original* discoverer; the law was first found by Thomas Harriot, about 1600 -- two decades before Snel's work.

I have some information about this at

http://mintaka.sdsu.edu/GF/explain/optics/discovery.html

----

An experimental paragraph added. See a short article by Kwan, Dudley and Lantz about this in Physics World in 2003 or 2002. This article says that Thomas Harriot (Hariot may be his preferred spelling) was actually not the first.
*I've improved the history section with information from that article, and incorporated the references in it. Hope that's clearer. I'm not sure what to do with the external link, which contradicts those articles (says Harriot was first). -- [[User:DrBob|Bob Mellish]] 17:36, 30 September 2005 (UTC)

Snell may be a solecism, but it's English, and it's the English name of the law, even if not how the man wrote his own name. Given how fluid spelling could be in the 17th century, it could be that Snell spelt his name in several different ways. Can someone check this?

== Image wrong? ==

The image shows that the normal is the boundary between the media, rather than being horizontal to the boundary. Also, <math>\theta_1</math> and <math>\theta_2</math> are wrongly labelled as a result. The image disagrees with the text. See ScienceWorld [http://scienceworld.wolfram.com/physics/SnellsLaw.html] for how the image should be corrected.

The image is misleading and confusing, and should be rectified as soon as possible; however, as I lack experience with graphics, I request someone to upload a corrected version as soon as possible.

*Um, no. The image is correct, and correctly labelled. The image in the article has the two media on the left and right sides of the diagram; the interface runs vertically. The image at Scienceworld has the two media at the top and bottom of their diagram; their interface runs horizontally. Try rotating one of the diagrams by 90°, and you'll see how they match. -- [[User:DrBob|Bob Mellish]] 18:25, 26 September 2005 (UTC)

== Snel's law spelling ==

I agree it is Snel and not Snell's law. Also in English. The 'discoverer' (not getting in the historical issue here, just the spelling bit) of the quantitative law of refraction was 'Willebrord Snel van Royen', thus one l, and there is no fluidity to this spelling as far as I know. The two-l-spelling has nothing to do with 'Snel' spelled differently in the English language but with incorrect de-latinazation of Snellius.

== Other formulae ==

I've seen this formula used quite a lot in some establishments as an expansion of the original law for wavelength... 

<math>\frac {\lambda_0}{\lambda_1} = \frac{v_o}{v_m} = \frac{c / n_1}{c / n_2} = \frac{n_2}{n_1}</math> to...
<math>\lambda_1 sin\theta_1 = \lambda_2 sin\theta_2</math> 

[[User:JSpudeman|James S]] 00:12, 11 December 2006 (UTC)

:Those ratios of velocities, wavelengths, indices of refraction, etc. are fine, but they are not Snell's law. Snell's law needs to have the sines of the angles in it. We seem to have forgotten to state the law near the top of the article anywhere. I'm working on it... [[User:Dicklyon|Dicklyon]] 20:04, 22 December 2006 (UTC)
:OK, I fixed the lead, putting the law equation and illustration into it; and I added a book page of history. I don't really understand the point of what someone was trying to do with these relations in the Explanation section, so I'll leave it for now. But as I said, without the angles, or some measurement proportional to their sines, it's not Snell's law. [[User:Dicklyon|Dicklyon]] 20:40, 22 December 2006 (UTC)

==Merge from Angle of refraction?==

I propose to merge [[Angle of refraction]] into Snell's law, since it covers exactly the same material. Please support, oppose, or otherwise comment here. [[User:Dicklyon|Dicklyon]] 08:36, 23 December 2006 (UTC)
:'''support''' [[User:The Photon|The Photon]] 03:46, 24 December 2006 (UTC)
:Expecting no objection, I went ahead and incorporated a few bits from there that we didn't have here, and converted it to a redirect. [[User:Dicklyon|Dicklyon]] 05:30, 24 December 2006 (UTC)

==Reverting JCraw's extensive uncommented changes==

JCRaw, that's a lot of changes to do all at once without even any change comments. You've de-linked the references from what they refer to, and made them into a very hard-to-maintain form (because the numbers don't track automatically). And you've introduced non-words (e.g. ''constance'') and grammatical errors into the lead. I haven't reviewed most of the changes yet, but on these bases alone I'm going to revert, and we can make the changes you want more slowly and carefully, giving other editors a chance to collaboration on them, please. [[User:Dicklyon|Dicklyon]] 17:00, 4 January 2007 (UTC)

JSpudeman, the way you've put it back is really no better. You still have the hard-to-maintain ref style, grammatical errors in the lead, and unclear what point you're trying to make there. The statement about "it's [sic] original form" is probably wrong, since the constant ratio of sines was articulated before velocities or indices of refraction were known. [[User:Dicklyon|Dicklyon]] 23:24, 4 January 2007 (UTC)

Point noted; i know of the application Fermat's principle to Snell's Law, but i was unaware of the history linking them together. However -- what was the original formula that was used before the inclusion of least-time? It would be interesting to know how the original formula was developed. On that note, do you own that book? I presume that from your reference to it's contents that you do? If so, why not reference it? [[User:JSpudeman|James S]] 23:23, 7 January 2007 (UTC)

==The original form of the law==

Here's [http://books.google.com/books?vid=OCLC13466184&id=ZwIAAAAAQAAJ&pg=RA4-PA295&lpg=RA4-PA295&dq=snell+sines+ratio+date:0-1820#PRA4-PA295,M1 an 1803 book] that explains that Snel did the same thing that [[Ibn Sahl]] had done. Nowhere does the velocity of propagation or the index of refraction enter into his observation that the ratio of sines is a constant for a given pair of media. Later, when it was realized that light speed varies in different media, it was realized that the law of sines was in agreement with a principle of least time, or [[Fermat's principle]]; that's where velocity and index started to come into the equation, via their ratio. Let's not get the cart before the horse on this. [[User:Dicklyon|Dicklyon]] 01:42, 5 January 2007 (UTC)

Talk:Snell's law

2007-01-07T23:21:51Z

JSpudeman: Fixed up your over-caps :-P

{{physics|class=B|importance=High}}
It would be nice to spell Snel's name correctly (i.e., with a single "l").
His name is "Snel" in his native language, or "Snellius" in Latin. The common spelling "Snell" is a solecism committed by people who know neither Dutch nor Latin.

Perhaps it would also be wise to point out that Snel was not the *original* discoverer; the law was first found by Thomas Harriot, about 1600 -- two decades before Snel's work.

I have some information about this at

http://mintaka.sdsu.edu/GF/explain/optics/discovery.html

----

An experimental paragraph added. See a short article by Kwan, Dudley and Lantz about this in Physics World in 2003 or 2002. This article says that Thomas Harriot (Hariot may be his preferred spelling) was actually not the first.
*I've improved the history section with information from that article, and incorporated the references in it. Hope that's clearer. I'm not sure what to do with the external link, which contradicts those articles (says Harriot was first). -- [[User:DrBob|Bob Mellish]] 17:36, 30 September 2005 (UTC)

Snell may be a solecism, but it's English, and it's the English name of the law, even if not how the man wrote his own name. Given how fluid spelling could be in the 17th century, it could be that Snell spelt his name in several different ways. Can someone check this?

== Image wrong? ==

The image shows that the normal is the boundary between the media, rather than being horizontal to the boundary. Also, <math>\theta_1</math> and <math>\theta_2</math> are wrongly labelled as a result. The image disagrees with the text. See ScienceWorld [http://scienceworld.wolfram.com/physics/SnellsLaw.html] for how the image should be corrected.

The image is misleading and confusing, and should be rectified as soon as possible; however, as I lack experience with graphics, I request someone to upload a corrected version as soon as possible.

*Um, no. The image is correct, and correctly labelled. The image in the article has the two media on the left and right sides of the diagram; the interface runs vertically. The image at Scienceworld has the two media at the top and bottom of their diagram; their interface runs horizontally. Try rotating one of the diagrams by 90°, and you'll see how they match. -- [[User:DrBob|Bob Mellish]] 18:25, 26 September 2005 (UTC)

== Snel's law spelling ==

I agree it is Snel and not Snell's law. Also in English. The 'discoverer' (not getting in the historical issue here, just the spelling bit) of the quantitative law of refraction was 'Willebrord Snel van Royen', thus one l, and there is no fluidity to this spelling as far as I know. The two-l-spelling has nothing to do with 'Snel' spelled differently in the English language but with incorrect de-latinazation of Snellius.

== Other formulae ==

I've seen this formula used quite a lot in some establishments as an expansion of the original law for wavelength... 

<math>\frac {\lambda_0}{\lambda_1} = \frac{v_o}{v_m} = \frac{c / n_1}{c / n_2} = \frac{n_2}{n_1}</math> to...
<math>\lambda_1 sin\theta_1 = \lambda_2 sin\theta_2</math> 

[[User:JSpudeman|James S]] 00:12, 11 December 2006 (UTC)

:Those ratios of velocities, wavelengths, indices of refraction, etc. are fine, but they are not Snell's law. Snell's law needs to have the sines of the angles in it. We seem to have forgotten to state the law near the top of the article anywhere. I'm working on it... [[User:Dicklyon|Dicklyon]] 20:04, 22 December 2006 (UTC)
:OK, I fixed the lead, putting the law equation and illustration into it; and I added a book page of history. I don't really understand the point of what someone was trying to do with these relations in the Explanation section, so I'll leave it for now. But as I said, without the angles, or some measurement proportional to their sines, it's not Snell's law. [[User:Dicklyon|Dicklyon]] 20:40, 22 December 2006 (UTC)

==Merge from Angle of refraction?==

I propose to merge [[Angle of refraction]] into Snell's law, since it covers exactly the same material. Please support, oppose, or otherwise comment here. [[User:Dicklyon|Dicklyon]] 08:36, 23 December 2006 (UTC)
:'''support''' [[User:The Photon|The Photon]] 03:46, 24 December 2006 (UTC)
:Expecting no objection, I went ahead and incorporated a few bits from there that we didn't have here, and converted it to a redirect. [[User:Dicklyon|Dicklyon]] 05:30, 24 December 2006 (UTC)

==Reverting JCraw's extensive uncommented changes==

JCRaw, that's a lot of changes to do all at once without even any change comments. You've de-linked the references from what they refer to, and made them into a very hard-to-maintain form (because the numbers don't track automatically). And you've introduced non-words (e.g. ''constance'') and grammatical errors into the lead. I haven't reviewed most of the changes yet, but on these bases alone I'm going to revert, and we can make the changes you want more slowly and carefully, giving other editors a chance to collaboration on them, please. [[User:Dicklyon|Dicklyon]] 17:00, 4 January 2007 (UTC)

JSpudeman, the way you've put it back is really no better. You still have the hard-to-maintain ref style, grammatical errors in the lead, and unclear what point you're trying to make there. The statement about "it's [sic] original form" is probably wrong, since the constant ratio of sines was articulated before velocities or indices of refraction were known. [[User:Dicklyon|Dicklyon]] 23:24, 4 January 2007 (UTC)

Point noted; i know of the application Fermat's principle to Snell's Law, but i was unaware of the history linking them together. However -- what was the original formula that was used before the inclusion of least-time? It would be interesting to know how the original formula was developed. On that note, do you own that book? If so, why not reference it?

==The original form of the law==

Here's [http://books.google.com/books?vid=OCLC13466184&id=ZwIAAAAAQAAJ&pg=RA4-PA295&lpg=RA4-PA295&dq=snell+sines+ratio+date:0-1820#PRA4-PA295,M1 an 1803 book] that explains that Snel did the same thing that [[Ibn Sahl]] had done. Nowhere does the velocity of propagation or the index of refraction enter into his observation that the ratio of sines is a constant for a given pair of media. Later, when it was realized that light speed varies in different media, it was realized that the law of sines was in agreement with a principle of least time, or [[Fermat's principle]]; that's where velocity and index started to come into the equation, via their ratio. Let's not get the cart before the horse on this. [[User:Dicklyon|Dicklyon]] 01:42, 5 January 2007 (UTC)

Physical chemistry

2007-01-07T22:50:18Z

JSpudeman: This needs fixing

'''Physical chemistry''' is the application of [[physics]] to macroscopic, microscopic, atomic and particulate phenomena in chemical systems<ref name="quanta_physical_chem_1" />within the field of chemistry traditionally using the principles, practices and concepts of [[thermodynamics]], [[quantum mechanics|quantum chemistry]], [[statistical mechanics]] and [[kinetics]] .<ref name="quanta_physical_chem_2" /> It is mostly defined as a large field of chemistry, in which, several sub-concepts are applied; the inclusion of quantum mechanics is used to illustrate the application of physical chemistry to atomic and particulate chemical interaction or experimentation <ref name="quanta_physical_chem_1" />.

Physical chemistry is mostly referred to as a macromolecular doctrine, as the majority of the principles on which physical chemistry was founded composed entirely of macromolecular concepts, such as [[colloids]]. <ref name="phys_chem_macro_1" />

The relationships that physical chemistry tries to resolve include the effects of:
#[[Intermolecular forces]] on the physical properties of materials ([[plasticity]], [[tensile strength]], [[surface tension]] in [[liquid]]s).
#[[Chemical kinetics|Reaction kinetics]] on the [[Reaction rate|rate of a reaction]].
#The identity of ions on the electrical conductivity of materials.

== History ==
The foundation of physical chemistry is thought to have started in [[1876]] by [[Josiah Willard Gibbs]] after the publishing of his paper ''On the Equilibrium of Heterogeneous Substances'', which contained several of the cornerstones of physical chemistry, such as [[gibbs free energy|gibbs energy]], [[chemical potential]]s, [[gibbs phase rule]] and subsequent naming and accredition of enthalpy to [[Heike Kamerlingh Onnes]] and to macromolecular processes. {{fact}}

== Notes ==
<noinclude>
<ref name="quanta_physical_chem_1">
'''Physical Chemistry''' (p3 - "PHYSICAL CHEMISTRY"), states that the field of physical chemistry is concerned with the microscopic and the macroscopic phenomenon which are mostly concerned with thermodynamics, and kinetics; the field of atomic and particulate interaction being included is implied with the inclusion of quantum chemistry.
</ref>

<ref name="quanta_physical_chem_2">
'''Quantum Chemistry''' (p3 - "PHYSICAL CHEMISTRY"), states that "We can divide physical chemistry into four areas: thermodynamics, quantum chemistry, statistical mechanics and kinetics".
</ref>

<ref name="phys_chem_macro_1">
'''Physical Chemistry of Macromolecules''' (p1 - "INTRODUCTION"), defines the formation of physical chemistry as being between macromolecules and colloids in modern physical chemistry. Also defines the "fierce battles" in the 1900's between the inclusion of colloids AS macromolecules.
</ref>
</noinclude>
<references />

== References ==
# Levine, I. N. (1978). ''Physical Chemistry'' McGraw-Hill publishing ISBN:0-07-037418-X
# Atkins, P. W. (1978). ''Physical Chemistry'' [[Oxford University Press]] ISBN:0-7167-3539-X
# Berry, S. R., Rice, S. A, Ross, J. (2000). ''Physical Chemistry'' 2nd ed. Oxford University Press. ISBN:0-19-510589-3
# Hunter, R. J. (1993) ''Introduction to Modern Colloid Science'' Oxford University Press. ISBN:0-19-855386-2
# Hiemenz, P. C., Rajagopalan, R., (1997). ''Principles of Colloid and Surface Chemistry'' Marcel Dekker Inc., New York. ISBN: 0-8247-9397-8
# Moore, W.J. (1963). ''Physical Chemistry'' 4th ed. Longman publishers/London/Prentice Hall, NJ.

==See also==
=== Sub-topics ===
* [[Energetics]]
* [[Thermochemistry]]
* [[Chemical kinetics]]
* [[Quantum chemistry]]
* [[Electrochemistry]]
* [[Surface chemistry]]
* [[Solid state chemistry|Solid-state chemistry]]
* [[spectroscopy]]
* [[Materials science]]
=== Publications ===
* [[List of important publications in chemistry#Physical chemistry|Important publications in physical chemistry(chemistry)]],
* [[list of important publications in physics#Physical chemistry|Important publications in physical chemistry(physics)]]
* [[Quantum chemistry]]

{{BranchesofChemistry}}

[[Category:Physical chemistry| ]]

{{physical-chemistry-stub}}

[[af:Fisiese chemie]]
[[ar:كيمياء فيزيائية]]
[[ca:Química Física]]
[[cs:Fyzikální chemie]]
[[da:Fysisk kemi]]
[[de:Physikalische Chemie]]
[[es:Fisicoquímica]]
[[eo:Fizika kemio]]
[[fa:شیمی فیزیک]]
[[fo:Alisevnafrøði]]
[[fr:Chimie physique]]
[[gl:Química Física]]
[[ko:물리화학]]
[[id:Kimia fisik]]
[[it:Chimica fisica]]
[[he:כימיה פיזיקלית]]
[[nl:Fysische chemie]]
[[ja:物理化学]]
[[nn:Fysikalsk kjemi]]
[[pl:Chemia fizyczna]]
[[pt:Físico-química]]
[[ru:Физическая химия]]
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[[zh:物理化学]]

Snell's law

2007-01-04T21:05:55Z

JSpudeman: Oops! Not a minor edit -- Changed the text to a more consise intro, resized pic and arranged. Added notes, and added static references section. Hope this is alright.

[[Image:Snells law.svg|thumb|300px|[[Refraction]] of light at the interface between two media of different [[refractive index|refractive indices]], with n2 > n1. Since the velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.]]

In [[physics]] and [[optics]], '''Snell's law''' (also known as '''Descartes' Law''' or the '''law of refraction''') is a [[mathematical formula|formula]] named after [[Dutch]] [[mathematics|mathematician]] [[Willebrord Snellius]], is and used to show the extent of directional change in a ray of light travelling between optical media. In it's original form, the formula describes the relationship between the angles of refraction, incidence and the refractive index between two given media as a [[constant]],<ref>'''Principles of Physics''' 4th ed. (p604,5) states; <math>n_1 \sin \theta_1 = n_2 \sin \theta_2</math> is the long form of <math>\frac{\sin \theta_1}{\sin \theta_2} = \frac{c/n_1}{c/n_2} = \frac{n_2}{n_1}</math>. It describes how to assemble snell's law from a given example using wavelength or angle changes. This would then mean that either the current or past version of snell's law is used to describe the relation between 2 refractive indeces as constant with the use of sines. </ref><ref>'''Ohanian, H. C. (1994)''', (p700) states the definition of snell's law through the resolving of the formulae for snell's law through the sines of the angles between the wavefronts of light incident upon a medium with a higher refractive index/phase velocity change the process follows from;
: <math> \sin \theta = \frac{c \Delta t}{PP'}</math> and <math>\sin \theta ' = \frac{(c/n)\Delta t}{PP'}</math>
: The ratio of the sines is therefore.. <math>\frac{\sin \theta}{\sin \theta '} = \frac{c}{c/n}</math>
: from which.. <math>sin \theta = n \sin \theta '</math>
: then finally .. <math>n_1 \sin \theta_1 = n_2 \sin \theta_2</math></ref> and is often applied to optical problems to determine angles of refraction or incidence and to calculate the refractive index of media such as water or glass, through the use of [[sine]]s.

The law is known historically as the "law of the sines"<ref>'''Whewell, W. (1837)''' p347 -- description of the "law of the sines" in reference to snell's law</ref>, and adheres to [[Fermat]]'s "''[[Fermat's principle|principle of least-time]]''", and has been adapted for other types of waves in [[isotropic|isotopic media]]. The law follows that the ratio of the [[sine]]s of the angles of incidence and refraction are equal to the ratio of [[velocities]] in the two media, or the inverse ratio of the indices of refraction:

:<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{n_2}{n_1}</math>

== History ==
[[Image:Snell Law of Sines 1837.png|thumb|right|An 1837 view of the history of "the Law of the Sines"]]
Snell's law was first discovered and described by [[Ibn Sahl]] in a manuscript written c.[[984]],<ref>'''Roshdi, R. (1990)''', p464-491 -- describes the work contributed to optics/formulation of snell's law by Ibn Sahl</ref> who used it to work out the shapes of lenses that focus light with no geometric aberrations, known as [[anaclastic lens]]es. It was discovered again by [[Thomas Harriot]] in [[1602]],<ref>'''Kwan, A., Dudley, J. Lantz, E. (2002)''', p64 -- text enquiring into the origin/discovery of Snell's Law.</ref> who did not publish his work.

In [[1621]], it was discovered yet again by Willebrord Snel, in a mathematically equivalent form, but unpublished during his lifetime. [[René Descartes]] independently derived the law using heuristic momentum conservation arguments in terms of sines in his [[1637]] treatise ''[[Discourse on Method]]'' (though detractors such as Fermat accused Descartes of working toward the already known answer with sophistic reasoning), and used it to solve a range of optical problems. Rejecting Descartes' solution, Pierre de Fermat arrived at the same solution based solely on his principal of least time.

In [[French language|French]], Snell's Law is called "la loi de Descartes" or "loi de Snell-Descartes."

== Explanation ==
Snell's law is used to determine the direction of light rays though refractive media with varying indices of refraction. The indices of refraction of the media, labeled <math>n_1,n_2</math> and so on, are used to represent the factor by which light is "slowed down" within a refractive medium, such as glass or water, compared to its velocity in a vacuum.

As light passes the border between media, depending upon the relative refractive indices of the two media, the light will either be refracted to a lesser angle, or a greater one. These angles are measured with respect to the ''normal line'', the perpendicular to the boundary. In the case of light traveling from air into water, light would be refrated towards the normal line, due to the fact that the light is slowed down in water; light traveling from water to air would refract away from the normal line.

Refraction between two surfaces is also referred to as ''reversible'' due to the fact that if all conditions were identical, the angles would be the same for light propagating in the opposite direction.

Snell's law is only generally true for isotropic media (such as [[glass]]). In [[anisotropic]] media such as some [[crystal]]s, [[birefringence]] may split the refracted ray into two rays, the ''ordinary'' or ''o''-ray which follows Snell's law, and the other ''extraordinary'' or ''e''-ray which may not be co-planar with the incident ray.

When the light or other wave involved is monochromatic, that is, of a single frequency, Snell's law can also be expressed in terms of a ratio of wavelengths in the two media, λ1 and λ2:

:<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{\lambda_1}{\lambda_2}</math>

=== Total internal reflection ===
[[Image:Refraction internal reflection diagram.PNG|thumb|220px|right|An example of the angles involved within total internal reflection.]]
When light moves from a dense to a less dense medium, such as from water to air, Snell's law cannot be used to calculate the refracted angle when the resolved sine value is higher than 1. At this point, light is reflected in the incident medium, known as internal reflection. Before the ray totally internally reflects, the light refracts at the '''critical angle'''; it travels directly along the surface between the two refractive media, without a change in phases like in other forms of optical phenomena.

As an example, a ray of light is incident at <math>50^o</math> towards a water–air boundary. If the angle is calculated using Snell's Law, then the resulting sine value will not invert, and thus the refracted angle cannot be calculated:

:<math>\theta_2 = \sin^{-1} (\frac{n_1}{n_2}\sin\theta_1) = \sin^{-1} (\frac{1.333}{1.000}0.766) = \sin^{-1} 1.021</math>

Snell's Law cannot calculate such angles because there is no refracted outgoing ray.

In order to calculate the critical angle, let <math>\theta_2 = 90^o</math> and solve for <math>\theta_\mathrm{crit}</math>:

:<math>\theta_{\mathrm{crit}} = \sin^{-1} \left( \frac{n_2}{n_1} \right)</math>

When θ1 > θcrit, no refracted ray appears, and the incident ray undergoes [[total internal reflection]] from the interface medium.

=== Derivations ===
Snell's law may be derived from [[Fermat's principle]], which states that the light travels the path which takes the least time. By taking the [[derivative]] of the [[optical path length]], the [[stationary point]] is found giving the path taken by the light (though it should be noted that the result does not show light taking the least time path, but rather one that is stationary with respect to small variations as there are cases where light actually takes the greatest time path, as in a spherical mirror).

Alternatively, Snell's law can be derived using interference of all possible paths of light wave from source to observer—it results in destructive interference everywhere except extrema of phase (where interference is constructive)—which become actual paths. In a classic analogy by [[Richard Feynman]], the area of lower refractive index is replaced by a beach, the area of higher refractive index by the sea, and the fastest way for a rescuer on the beach to get to a [[drowning]] person in the sea is to run along a path that follows Snell's law.

Another way to derive Snell’s Law involves an application of the general [[boundary conditions]] of [[Maxwell equations]] for [[electromagnetic radiation]].

== Uses ==
=== Calculating refractive indices ===

In the diagram on the right, two media of refractive indices ''n''1 (on the left) and ''n''2 (on the right) meet at a surface or interface (vertical line). ''n''2 > ''n''1, and light has a slower [[phase velocity]] within the second medium.

A light ray '''PO''' in the leftmost medium strikes the interface at the point '''O'''. From point '''O''', we project a straight line at right angles to the line of the interface; this is known as the [[Surface normal|normal]] to the surface (horizontal line). The angle between the normal and the light ray '''PO''' is known as the ''angle of incidence'', θ1.

The ray continues through the interface into the medium on the right; this is shown as the ray '''OQ'''. The angle it makes to the normal is known as the ''angle of refraction'', θ2.

:<math>n_1 \sin\theta_1 = n_2 \sin\theta_2 </math> or <math>\sum_{k=x,y}^N x=n_x\sin\theta_x,n_y \sin\theta_y</math>
:<math>\frac{n_1}{n_2} = \frac{\sin\theta_2}{\sin\theta_1}</math>
Note that, for the case of θ1 = 0° (i.e., a ray perpendicular to the interface) the solution is θ2 = 0° regardless of the values of ''n''1 and ''n''2-- a ray entering a medium perpendicular to the surface is never bent.

The above is also valid for light going from a dense to a less dense medium; the symmetry of Snell's law shows that the same ray paths are applicable in opposite direction.

A qualitative rule for determining the direction of refraction is that the ray in the denser medium is always closer to the normal. An analogy often used to remember this is done by visualizing the ray as a car crossing the boundary between asphalt (the less dense medium) and mud (the denser medium). Depending on the angle, either the left wheel or the right wheel of the car will cross into the new medium first, causing the car to swerve.

=== Vector form ===

Given a normalized ray vector '''v''' and a normalized plane normal vector '''p''', one can work out the normalized reflected and refracted rays: (note that the actual angles θ1 and θ2 are not worked out)

:<math>\cos\theta_1=\mathbf{v}\cdot\mathbf{p}</math>
:<math>\cos\theta_2=\sqrt{1-\left(\frac{n_1}{n_2}\right)^2\left(1-\left(\cos\theta_1\right)^2\right)}</math>
:<math>\mathbf{v}_{\mathrm{reflect}}=\mathbf{v}-\left(2\cos\theta_1\right)\mathbf{p}</math>
:<math>\mathbf{v}_{\mathrm{refract}}=\left(\frac{n_1}{n_2}\right)\mathbf{v} + \left(\cos\theta_2 - \frac{n_1}{n_2}\cos\theta_1\right)\mathbf{p}</math>
Note: <math>\mathbf{v}\cdot\mathbf{p}</math> must be positive.

The cosines may be recycled and used in the [[Fresnel equations]] for working out the intensity of the resulting rays. During total internal reflection an [[evanescent wave]] is produced, which [[exponential decay|rapidly decays]] from the surface into the second medium. Conservation of energy is maintained by the circulation of energy across the boundary, averaging to zero net energy transmission.

==Dispersion==

In many wave-propagation media, wave velocity changes with frequency or wavelength of the waves; this is true of light propagation in most transparent substances other than a vacuum. These media are called dispersive. The result is that the angles determined by Snell's law also depend on frequency or wavelength, so that a ray of mixed wavelengths, such as white light, will spread or disperse. Such dispersion of light in glass or water underlies the origin of [[rainbow]]s, since different wavelenghts appear as different colors.

In optical instruments, [[dispersion (optics)|dispersion]] leads to [[chromatic aberration]], a color-dependent blurring that sometimes is the resolution-limiting effect. This was especially true in [[refracting telescope]]s, before the invention of achromatic objective lenses.

==See also==

* [[Fresnel equations]]
* [[Reflection (physics)|Reflection]]
* [[Refraction]]
* [[Total internal reflection]]
* [[Evanescent wave]]

== Notes ==
<references />

== References ==
# Bueche, F. (1982). ''Principles of Physics'', 4th ed. McGraw-Hill International
# Ohanian, H. C. (1994) ''Principles of Physics'' W.W. Norton & Company
# Whewell, W. (1837). ''History of the Inductive Science from the Earliest to the Present Times'', London: John H. Parker
# {{cite journal | author=Rashed, Roshdi | title= A pioneer in anaclastics: Ibn Sahl on burning mirrors and lenses | journal= ISIS | year= 1990| volume= 81| pages= 464–491 }}
# {{cite journal | author=Kwan, A., Dudley, J., and Lantz, E. | title=Who really discovered Snell's law? | journal=Physics World | year=2002 | volume=15 | issue=4 | pages=64 }}

== External links ==

* [http://mintaka.sdsu.edu/GF/explain/optics/discovery.html Discovery of the law of refraction]

[[Category:Geometrical optics]]
[[Category:Introductory physics]]
[[Category:Eponymous laws]]

[[cs:Snellův zákon]]
[[de:Snelliussches Brechungsgesetz]]
[[es:Ley de Snell]]
[[fr:Lois de Snell-Descartes]]
[[it:Legge di Snell]]
[[he:חוק סנל]]
[[nl:Wet van Snellius]]
[[ja:スネルの法則]]
[[no:Snells brytningslov]]
[[pl:Prawo Snelliusa]]
[[ru:Закон Снелла]]
[[sl:Lomni zakon]]
[[sv:Snells lag]]
[[zh:光的折射定律]]

Snell's law

2007-01-04T21:04:12Z

JSpudeman: I haven't got the books,but i will try to verify. Other than that, i made the introduction more concise and grammatically correct, and changed the referencing back. (Image resized for niceness.)

[[Image:Snells law.svg|thumb|300px|[[Refraction]] of light at the interface between two media of different [[refractive index|refractive indices]], with n2 > n1. Since the velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.]]

In [[physics]] and [[optics]], '''Snell's law''' (also known as '''Descartes' Law''' or the '''law of refraction''') is a [[mathematical formula|formula]] named after [[Dutch]] [[mathematics|mathematician]] [[Willebrord Snellius]], is and used to show the extent of directional change in a ray of light travelling between optical media. In it's original form, the formula describes the relationship between the angles of refraction, incidence and the refractive index between two given media as a [[constant]],<ref>'''Principles of Physics''' 4th ed. (p604,5) states; <math>n_1 \sin \theta_1 = n_2 \sin \theta_2</math> is the long form of <math>\frac{\sin \theta_1}{\sin \theta_2} = \frac{c/n_1}{c/n_2} = \frac{n_2}{n_1}</math>. It describes how to assemble snell's law from a given example using wavelength or angle changes. This would then mean that either the current or past version of snell's law is used to describe the relation between 2 refractive indeces as constant with the use of sines. </ref><ref>'''Ohanian, H. C. (1994)''', (p700) states the definition of snell's law through the resolving of the formulae for snell's law through the sines of the angles between the wavefronts of light incident upon a medium with a higher refractive index/phase velocity change the process follows from;
: <math> \sin \theta = \frac{c \Delta t}{PP'}</math> and <math>\sin \theta ' = \frac{(c/n)\Delta t}{PP'}</math>
: The ratio of the sines is therefore.. <math>\frac{\sin \theta}{\sin \theta '} = \frac{c}{c/n}</math>
: from which.. <math>sin \theta = n \sin \theta '</math>
: then finally .. <math>n_1 \sin \theta_1 = n_2 \sin \theta_2</math></ref> and is often applied to optical problems to determine angles of refraction or incidence and to calculate the refractive index of media such as water or glass, through the use of [[sine]]s.

The law is known historically as the "law of the sines"<ref>'''Whewell, W. (1837)''' p347 -- description of the "law of the sines" in reference to snell's law</ref>, and adheres to [[Fermat]]'s "''[[Fermat's principle|principle of least-time]]''", and has been adapted for other types of waves in [[isotropic|isotopic media]]. The law follows that the ratio of the [[sine]]s of the angles of incidence and refraction are equal to the ratio of [[velocities]] in the two media, or the inverse ratio of the indices of refraction:

:<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{n_2}{n_1}</math>

== History ==
[[Image:Snell Law of Sines 1837.png|thumb|right|An 1837 view of the history of "the Law of the Sines"]]
Snell's law was first discovered and described by [[Ibn Sahl]] in a manuscript written c.[[984]],<ref>'''Roshdi, R. (1990)''', p464-491 -- describes the work contributed to optics/formulation of snell's law by Ibn Sahl</ref> who used it to work out the shapes of lenses that focus light with no geometric aberrations, known as [[anaclastic lens]]es. It was discovered again by [[Thomas Harriot]] in [[1602]],<ref>'''Kwan, A., Dudley, J. Lantz, E. (2002)''', p64 -- text enquiring into the origin/discovery of Snell's Law.</ref> who did not publish his work.

In [[1621]], it was discovered yet again by Willebrord Snel, in a mathematically equivalent form, but unpublished during his lifetime. [[René Descartes]] independently derived the law using heuristic momentum conservation arguments in terms of sines in his [[1637]] treatise ''[[Discourse on Method]]'' (though detractors such as Fermat accused Descartes of working toward the already known answer with sophistic reasoning), and used it to solve a range of optical problems. Rejecting Descartes' solution, Pierre de Fermat arrived at the same solution based solely on his principal of least time.

In [[French language|French]], Snell's Law is called "la loi de Descartes" or "loi de Snell-Descartes."

== Explanation ==
Snell's law is used to determine the direction of light rays though refractive media with varying indices of refraction. The indices of refraction of the media, labeled <math>n_1,n_2</math> and so on, are used to represent the factor by which light is "slowed down" within a refractive medium, such as glass or water, compared to its velocity in a vacuum.

As light passes the border between media, depending upon the relative refractive indices of the two media, the light will either be refracted to a lesser angle, or a greater one. These angles are measured with respect to the ''normal line'', the perpendicular to the boundary. In the case of light traveling from air into water, light would be refrated towards the normal line, due to the fact that the light is slowed down in water; light traveling from water to air would refract away from the normal line.

Refraction between two surfaces is also referred to as ''reversible'' due to the fact that if all conditions were identical, the angles would be the same for light propagating in the opposite direction.

Snell's law is only generally true for isotropic media (such as [[glass]]). In [[anisotropic]] media such as some [[crystal]]s, [[birefringence]] may split the refracted ray into two rays, the ''ordinary'' or ''o''-ray which follows Snell's law, and the other ''extraordinary'' or ''e''-ray which may not be co-planar with the incident ray.

When the light or other wave involved is monochromatic, that is, of a single frequency, Snell's law can also be expressed in terms of a ratio of wavelengths in the two media, λ1 and λ2:

:<math>\frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2} = \frac{\lambda_1}{\lambda_2}</math>

=== Total internal reflection ===
[[Image:Refraction internal reflection diagram.PNG|thumb|220px|right|An example of the angles involved within total internal reflection.]]
When light moves from a dense to a less dense medium, such as from water to air, Snell's law cannot be used to calculate the refracted angle when the resolved sine value is higher than 1. At this point, light is reflected in the incident medium, known as internal reflection. Before the ray totally internally reflects, the light refracts at the '''critical angle'''; it travels directly along the surface between the two refractive media, without a change in phases like in other forms of optical phenomena.

As an example, a ray of light is incident at <math>50^o</math> towards a water–air boundary. If the angle is calculated using Snell's Law, then the resulting sine value will not invert, and thus the refracted angle cannot be calculated:

:<math>\theta_2 = \sin^{-1} (\frac{n_1}{n_2}\sin\theta_1) = \sin^{-1} (\frac{1.333}{1.000}0.766) = \sin^{-1} 1.021</math>

Snell's Law cannot calculate such angles because there is no refracted outgoing ray.

In order to calculate the critical angle, let <math>\theta_2 = 90^o</math> and solve for <math>\theta_\mathrm{crit}</math>:

:<math>\theta_{\mathrm{crit}} = \sin^{-1} \left( \frac{n_2}{n_1} \right)</math>

When θ1 > θcrit, no refracted ray appears, and the incident ray undergoes [[total internal reflection]] from the interface medium.

=== Derivations ===
Snell's law may be derived from [[Fermat's principle]], which states that the light travels the path which takes the least time. By taking the [[derivative]] of the [[optical path length]], the [[stationary point]] is found giving the path taken by the light (though it should be noted that the result does not show light taking the least time path, but rather one that is stationary with respect to small variations as there are cases where light actually takes the greatest time path, as in a spherical mirror).

Alternatively, Snell's law can be derived using interference of all possible paths of light wave from source to observer—it results in destructive interference everywhere except extrema of phase (where interference is constructive)—which become actual paths. In a classic analogy by [[Richard Feynman]], the area of lower refractive index is replaced by a beach, the area of higher refractive index by the sea, and the fastest way for a rescuer on the beach to get to a [[drowning]] person in the sea is to run along a path that follows Snell's law.

Another way to derive Snell’s Law involves an application of the general [[boundary conditions]] of [[Maxwell equations]] for [[electromagnetic radiation]].

== Uses ==
=== Calculating refractive indices ===

In the diagram on the right, two media of refractive indices ''n''1 (on the left) and ''n''2 (on the right) meet at a surface or interface (vertical line). ''n''2 > ''n''1, and light has a slower [[phase velocity]] within the second medium.

A light ray '''PO''' in the leftmost medium strikes the interface at the point '''O'''. From point '''O''', we project a straight line at right angles to the line of the interface; this is known as the [[Surface normal|normal]] to the surface (horizontal line). The angle between the normal and the light ray '''PO''' is known as the ''angle of incidence'', θ1.

The ray continues through the interface into the medium on the right; this is shown as the ray '''OQ'''. The angle it makes to the normal is known as the ''angle of refraction'', θ2.

:<math>n_1 \sin\theta_1 = n_2 \sin\theta_2 </math> or <math>\sum_{k=x,y}^N x=n_x\sin\theta_x,n_y \sin\theta_y</math>
:<math>\frac{n_1}{n_2} = \frac{\sin\theta_2}{\sin\theta_1}</math>
Note that, for the case of θ1 = 0° (i.e., a ray perpendicular to the interface) the solution is θ2 = 0° regardless of the values of ''n''1 and ''n''2-- a ray entering a medium perpendicular to the surface is never bent.

The above is also valid for light going from a dense to a less dense medium; the symmetry of Snell's law shows that the same ray paths are applicable in opposite direction.

A qualitative rule for determining the direction of refraction is that the ray in the denser medium is always closer to the normal. An analogy often used to remember this is done by visualizing the ray as a car crossing the boundary between asphalt (the less dense medium) and mud (the denser medium). Depending on the angle, either the left wheel or the right wheel of the car will cross into the new medium first, causing the car to swerve.

=== Vector form ===

Given a normalized ray vector '''v''' and a normalized plane normal vector '''p''', one can work out the normalized reflected and refracted rays: (note that the actual angles θ1 and θ2 are not worked out)

:<math>\cos\theta_1=\mathbf{v}\cdot\mathbf{p}</math>
:<math>\cos\theta_2=\sqrt{1-\left(\frac{n_1}{n_2}\right)^2\left(1-\left(\cos\theta_1\right)^2\right)}</math>
:<math>\mathbf{v}_{\mathrm{reflect}}=\mathbf{v}-\left(2\cos\theta_1\right)\mathbf{p}</math>
:<math>\mathbf{v}_{\mathrm{refract}}=\left(\frac{n_1}{n_2}\right)\mathbf{v} + \left(\cos\theta_2 - \frac{n_1}{n_2}\cos\theta_1\right)\mathbf{p}</math>
Note: <math>\mathbf{v}\cdot\mathbf{p}</math> must be positive.

The cosines may be recycled and used in the [[Fresnel equations]] for working out the intensity of the resulting rays. During total internal reflection an [[evanescent wave]] is produced, which [[exponential decay|rapidly decays]] from the surface into the second medium. Conservation of energy is maintained by the circulation of energy across the boundary, averaging to zero net energy transmission.

==Dispersion==

In many wave-propagation media, wave velocity changes with frequency or wavelength of the waves; this is true of light propagation in most transparent substances other than a vacuum. These media are called dispersive. The result is that the angles determined by Snell's law also depend on frequency or wavelength, so that a ray of mixed wavelengths, such as white light, will spread or disperse. Such dispersion of light in glass or water underlies the origin of [[rainbow]]s, since different wavelenghts appear as different colors.

In optical instruments, [[dispersion (optics)|dispersion]] leads to [[chromatic aberration]], a color-dependent blurring that sometimes is the resolution-limiting effect. This was especially true in [[refracting telescope]]s, before the invention of achromatic objective lenses.

==See also==

* [[Fresnel equations]]
* [[Reflection (physics)|Reflection]]
* [[Refraction]]
* [[Total internal reflection]]
* [[Evanescent wave]]

== Notes ==
<references />

== References ==
# Bueche, F. (1982). ''Principles of Physics'', 4th ed. McGraw-Hill International
# Ohanian, H. C. (1994) ''Principles of Physics'' W.W. Norton & Company
# Whewell, W. (1837). ''History of the Inductive Science from the Earliest to the Present Times'', London: John H. Parker
# {{cite journal | author=Rashed, Roshdi | title= A pioneer in anaclastics: Ibn Sahl on burning mirrors and lenses | journal= ISIS | year= 1990| volume= 81| pages= 464–491 }}
# {{cite journal | author=Kwan, A., Dudley, J., and Lantz, E. | title=Who really discovered Snell's law? | journal=Physics World | year=2002 | volume=15 | issue=4 | pages=64 }}

== External links ==

* [http://mintaka.sdsu.edu/GF/explain/optics/discovery.html Discovery of the law of refraction]

[[Category:Geometrical optics]]
[[Category:Introductory physics]]
[[Category:Eponymous laws]]

[[cs:Snellův zákon]]
[[de:Snelliussches Brechungsgesetz]]
[[es:Ley de Snell]]
[[fr:Lois de Snell-Descartes]]
[[it:Legge di Snell]]
[[he:חוק סנל]]
[[nl:Wet van Snellius]]
[[ja:スネルの法則]]
[[no:Snells brytningslov]]
[[pl:Prawo Snelliusa]]
[[ru:Закон Снелла]]
[[sl:Lomni zakon]]
[[sv:Snells lag]]
[[zh:光的折射定律]]

User talk:Dicklyon

2007-01-04T19:31:50Z

JSpudeman: Sorry, Dickylon i should have read the talk page; thanks

User talk:Dicklyon

2007-01-04T19:14:18Z

JSpudeman: Revert to Snell's Law