# A student uses a joulemeter to investigate the efficiency of an electric motor lifting a load. The joulemeter shows that 600 J of energy is supplied to the motor. The useful energy transferred to the load is 210 J. Explain why the efficiency of this motor cannot equal 1, and describe what happens to the energy that is not usefully transferred.

> Eduqas GCSE Physics — 1.6 Distance, speed and acceleration · Explain · 4 marks

> An electric motor is used to lift a heavy load. A joulemeter measures the total energy supplied to the motor.

## Mark scheme (4 marks)

1. The law of conservation of energy means energy cannot be created or destroyed, only transferred or dissipated
2. Some energy is always dissipated / transferred as waste energy, so useful output is always less than total input
3. The energy that is not usefully transferred is a waste energy transfer, for example as heat/thermal energy
4. This waste energy transfer does not directly serve the purpose of the system / is not a useful energy transfer

## Key terms

- [efficiency](https://www.gradenine.co.uk/glossary/efficiency)
- [useful energy transfer](https://www.gradenine.co.uk/glossary/useful-energy-transfer)
- [joulemeter](https://www.gradenine.co.uk/glossary/joulemeter)

## Related

- [Revision notes for Eduqas GCSE Physics](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-uses-a-joulemeter-to-ed510868) · Published by Druglandscape Ltd.