Efficiency (Also seen in GCSE Physics 1)

We already know that the efficiency of a device is a measure of how much of the energy we put in is wasted.

Efficiency = useful energy transferred by the device this will give us a number less than 1

total energy supplied to the device

Useful energy means the energy transferred for a purpose, the energy transferred into the desired form.

Since power is calculated from energy we can express efficiency as:

Efficiency = useful output power of the device again this will give us a number less than 1

input power to the device

To calculate the efficiency as a percentage use the following:

percentage efficiency = efficiency x 100%