Power is the energy transferred per unit time. Power is measured in watts (W), energy in joules (J) and time in seconds (s). 1 W = 1 J/s (1 watt is 1 joule per second.) Electrical power can be ...

A very inefficient device will waste most of its input energy. The efficiency of a device is the proportion of the energy supplied that is transferred in useful ways. The efficiency can be ...