Power (physics)

In physics, power is the amount of work done per unit of time. This is equivalent to the rate of change of the energy in a system, or the time rate of doing work, as defined by the formula

P = dW/dt

where P is power, W is work done, and t is time. Power may be expressed in units of work per unit time (eg, foot-pounds per minute or ergs per second) or more arbitrarily as in horsepower or watts. One horsepower is 33,000 foot-pounds per minute.

The watt (W) is the SI unit of power, and is defined as one joule per second (W = J/s). Power can also be measured in the English unit of horsepower, which is defined as the power required to move 550 pounds one foot in one second (roughly 746 watts depending on who you ask, but apparently no one has the exact same horse). Other units of measure for power include the Pferdstarke (PS) and Cheveaux (CV), used in France.

The power consumed by a two-terminal electrical device is the product of the voltage across the terminals and the current passing between them. 1 watt equals 1 volt × 1 ampere.