Power is the rate at which work is performed or energy is transferred. The units of power are units of energy divided by time. Power = Work / Time.

The watt is the SI derived unit of power, equal to one joule per second. Also, electric power is defined as the amount of work done by an electric current, or the rate at which electrical energy is transmitted. When electric current flows in a circuit with resistance, it does work. Devices convert this work into many useful forms, such as heat, light, motion and sound.