GCSE Physics

Calculating Efficiency

It's time for a worked example!

e.g. An electric motor is used to lift a 0.6 kg mass through a height of 1 m. The energy it uses is measured on an energy meter: 10 J.

The useful work done lifting it is found from the gravitational potential energy formula:
GPE = mgh = 0.6 × 10 × 1 = 6 J

So the efficiency can now be found:
efficiency = useful energy transferred / total energy used = 6 / 10 = 0.6 (or 60%)

This is a quite efficient motor, yet electric motors used in modern electric/hybrid cars are nearly 100% efficient (the Honda Civic Hybrid's motor is 97.5% efficient!)

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