# A student uses an electric fan heater to warm a room. Describe the useful energy transfer and the waste energy transfer that occur when the fan heater operates. Then explain, using the law of conservation of energy, why the efficiency of the fan heater can never exceed 100%.

> WJEC A-Level Physics (Wales) — 1.3 Energy concepts · Describe and Explain · 5 marks

> An electric fan heater is designed to heat a room. It takes in electrical energy and transfers it in several ways.

## Mark scheme (5 marks)

1. The useful energy transfer is the transfer of electrical energy to thermal (heat) energy that warms the room
2. The waste energy transfer is the transfer of electrical energy to sound energy (from the fan motor) that does not directly serve the purpose of heating the room
3. The law of conservation of energy states that energy can be transferred, stored or dissipated but never created or destroyed
4. The useful output energy can never be greater than the total input energy because no extra energy can be created
5. Some input energy is always dissipated as waste energy transfer, so the useful output energy is always less than the total input energy, meaning efficiency is always less than 100%

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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-an-electric-fan-6d87402e) · Published by Druglandscape Ltd.