Power is the rate at which energy is supplied or transferred, or, equivalently, the rate at which work is done, dW /dt. If the force that is doing the work is constant, then the power, P = F ds /dt , i.e., P = Fv.
The SI unit of power is the watt (W); it is equivalent to the joule per second (J s–1) or kg m2 s–3. Power has dimensions [M ] 1 [L ] 2 [T ] –3.
While mechanical power may be derived as a product of a force and a velocity (linear or angular), the electrical power utilized in a circuit is a product of the potential drop and the current flowing in it (volts × amperes = watts). Where the electrical supply is alternating, the root-mean-square (rms) value of the voltage must be used.