# A factory uses an electric motor to lift heavy crates. The motor has a power rating of 500 W but only 350 W is used to raise the crates. Explain why the efficiency of the motor cannot equal 1 (100%), and describe two ways the manufacturer could improve the efficiency of the motor.

> OCR GCSE Physics A: Gateway Science (J249) — P5.2 Power and efficiency · Explain · 4 marks

> An electric motor in a factory is used to lift crates. Not all of the electrical energy supplied to the motor is transferred usefully — some is wasted as heat and sound during operation.

## Mark scheme (4 marks)

1. The efficiency cannot equal 1 (100%) because some energy is transferred as waste (e.g. heat/sound) rather than as useful energy transfer, and energy cannot be created or destroyed.
2. Lubrication of the motor's moving parts reduces friction, which reduces waste heat energy transfer, improving efficiency.
3. Reducing the current through the motor decreases power lost to heating of wires (since power loss = I²R), reducing waste energy transfer.
4. Recycling or recovering waste energy (e.g. capturing waste heat) means energy that would be dissipated is reused, increasing the useful output relative to total input.

## Key terms

- [efficiency](https://www.gradenine.co.uk/glossary/efficiency)
- [power rating](https://www.gradenine.co.uk/glossary/power-rating)

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](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-factory-uses-an-electric-motor-8ae5bb6f) · Published by Druglandscape Ltd.