Electricity
In physics, the phenomenon of electricity or electric charge is a conserved property of matter that can be quantified. In this sense, the phrase "quantity of electricity" is used interchangeably with the phrases "charge of electricity" and "quantity of charge." There are two types of electricity or charge: we call one kind of charge positive and the other negative. Through experiment, we find that like-charged objects repel and opposite-charged objects attract one another. The magnitude of the force of attraction or repulsion is given by Coulomb's Law.
The SI unit of electrical charge is the coulomb.
History
In June, 1752, Benjamin Franklin flew kites in thunderstorms, capturing electric charges from lightning bolts as they traveled down the kite-string.
While Franklin may not have "discovered" electricity -- it was observed in ancient times -- he did invent the lightning rod and establish a link between lightning and electricity. Franklin's observations aided later scientists such as Michael Faraday, Alessandro Volta, André-Marie Ampère, and Georg Simon Ohm whose work provided the basis for modern electrical technology. The work of Faraday, Volta, Ampere, and Ohm is honored by society, in that fundamental units of measurement are named after them.
Volta worked with chemicals and discovered that chemical reactions could be used to create positively charged anodes and negatively charged cathodes. When a conductor was attached between these, the difference in the electrical potential (also known as voltage) drives a current between them through the conductor. The potential difference between two points is measured in units of volts in recognition of Volta's work.
The late 19th and early 20th century produced such giants of electrical engineering such as Samuel F.B. Morse, inventor of the telegraph; Alexander Graham Bell, inventor of the telephone; Thomas Edison (inventor of the incandescent light bulb, phonograph and motion pictures); George Westinghouse, inventor of the electric locomotive; Charles Steinmetz, inventor of alternating current; and Nikola Tesla, inventor of hte induction motor. Tesla is said to have performed experiments with very high voltages that are the stuff of legend, involving ball lightning and other effects that no one has ever publicly duplicated or explained.
In May 1885, Westinghouse, then president of the Westinghouse Electric Company in Pittsburgh, Pennsylvania, bought the rights to Tesla's patents for polyphase alternating-current dynamos. This led to a contest in the so-called court of public opinion as to which system would be adopted as the standard for power transmission, Edison's direct-current system or Westinghouse's alternating-current method.
Edison conducted a spirited public relations campaign which included his promoting of the electric chair as a method of execution. The electric chair ran on Westinghouse's AC; Edison wanted to prove that AC power was capable of killing, and should therefore be viewed by the public as inherently dangerous. AC power transmission was eventually (and deservedly) adopted as the standard.
Electric power, for most consumers, is generated centrally by utility companies using coal, oil, hydropower, or nuclear power. In 2000, U.S. electric utilities had 600 gigawatts of maximum summer generating capacity including 261 GW from coal, 41 GW from petroleum, 118 GW from natural gas, 92 GW from hydropower and 86 GW from nuclear fuels. Little generating capacity is presently based on renewable sources such as solar power and wind power. Some individuals and communities prefer renewable sources because there is less pollution, and because users of renewable electricity sources can sometimes gain a measure of economic independence from the electrical utilities.
Some solar and wind power is generated,
Things that are powered by electricity include lamps; computers and the internet; radio and television; refrigeration; air conditioning; traffic signals; electric guitars and other electronic musical instruments; the spark plugs in your automobile;
Today, for residents of most developed countries, 24-hour, on-demand, access to electrical power is taken for granted. People gripe about their electric bill and about electric power monopolies and utility pricing, but by any comparison with pre-industrial standards of living times electricity is still a bargain. Few would want to go back to life without it.
In electrical engineering, the energy in electromagnetic fields is harnessed to perform useful work - either as a method to transmit energy to the appropriate place and then convert it back into a different, useful form of energy (for instance, heat, light, or motion), or by using the presence or level of electricity to convey information.
Today's electrical engineers enjoy the ability to design circuits using pre-manufactured building blocks such as power supplies, resistors, capacitors, semiconductors such as transistors, and integrated circuits. An integrated circuit inside your computer, a microprocessor, performs thousands of computations per second. Yet the microprocessor, like other digital integrated circuits, runs on 5 volts of direct current electricity.
A flow of electricity is known as an electric current. A direct current (DC) is a constant flow between two points having a different electrical potential. By convention, a positive current is defined as that which flows from a higher potential to a lesser one, driven by the potential difference.
It is often important, particularly for safety reasons, that one side of a circuit be electrically bonded to an earth terminal. Such an earth terminal is usually connected to an electrode buried in the ground. The potential of earth ground is defined as zero by convention, and the electrical conductivity between similarly buried electrodes is considered to be low enough that all earth terminals are effectively at the same voltage.
Flows of electric charge can be produced within conductors and cannot exist within insulators. Some electrical devices that use electrical physics are called electronic devices. See electrical conduction for more information about current flow in materials.
Ohm's Law is an important relationship describing the behaviour of electric currents in conductors: voltage potential difference = current * resistance, or:
V = IR
Electrical phenomena in nature
- Many animals are sensitive to electric fields, some (e.g., sharks) more than others (e.g., people). A few, such as the electric eel, generate their own electric fields.
Terminology Issues
In addition to its definition by physicists, the word electricity has several popular definitions which are contradictory. Rather than using the word electricity to refer to the quantity of electric charge, many sources instead say that electricity is the quantity of electromagnetic energy measured in joules or kilowatt-hours. Other sources call the flow of charges within a conductor by the name electricity and they measure the quantity of electricity in terms of amperes. Still others call a wide variety of electrical phenomena by the name electricity, e.g. bioelectricity, piezoelectricity, triboelectricity, etc. The student is advised to be extremely careful when interpreting texts which use the frequently misused term electricity in place of the more accurate terms electric charge, electric current, electrical energy, etc.
See also: electric power (for energy transfer using electricity), battery.