Power as energy transferred per second

Power is the rate at which energy is transferred, which means the energy transferred per second. It is measured in watts (W). One watt is a transfer of one joule each second, so 1 W = 1 J/s. A kilowatt (kW) is 1000 W.

A 60 W lamp transfers 60 J every second. A heater with a power of 2 kW transfers 2000 J every second. A device with a higher power rating transfers energy faster than one with a lower rating.