# A tumble dryer uses electrical energy to dry clothes. The tumble dryer transfers 600 J of electrical energy in one cycle. Of this, 450 J is transferred as useful thermal energy to the clothes. Explain what is meant by waste energy transfer in this context and describe TWO ways in which the efficiency of the tumble dryer could be increased.

> Edexcel A-Level Physics (9PH0) — 3.2 EMF, resistance and circuits · Explain · 5 marks

> A tumble dryer contains a rotating drum driven by an electric motor. The drum spins the clothes whilst hot air is blown through them. The motor and the drum both produce unwanted energy transfers during operation.

## Mark scheme (5 marks)

1. Waste energy transfer is energy transferred by the tumble dryer to a form that does not directly serve the purpose of drying clothes
2. Identifies a correct form of waste energy in context, e.g. heat from the motor / sound from the rotating drum
3. First method: lubrication of the drum / motor to reduce friction, so less energy is wasted as heat
4. First method linked to efficiency: less energy is wasted so a greater proportion of the input energy is transferred usefully, increasing efficiency
5. Second method: thermal insulation of the drum casing to reduce heat lost to the surroundings, so more energy is available as useful output

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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-tumble-dryer-uses-electrical-energy-3fabaeb1) · Published by Druglandscape Ltd.