# A electric kettle is used to boil water. Explain why the kettle is not 100% efficient, and describe what happens to the energy that is not usefully transferred.

> WJEC GCSE Physics (Wales) — 1.6 Distance, speed and acceleration · Explain · 4 marks

> An electric kettle has a power rating of 2 kW. When in use, not all of the electrical energy is transferred usefully.

## Mark scheme (4 marks)

1. The useful energy transfer is heating the water (to boiling point)
2. Some energy is transferred as waste energy (e.g. heating the surroundings / the kettle body / sound)
3. Because energy cannot be created or destroyed (conservation of energy), the total energy input always equals useful plus waste output
4. Efficiency cannot reach 1 (100%) because some energy is always transferred as waste energy transfer rather than useful energy transfer

## Related

- [Revision notes for WJEC GCSE Physics (Wales)](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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