# A electric kettle is used to heat water. Explain why the useful energy transferred to the water is always less than the total electrical energy input to the kettle.

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

> An electric kettle has a power-rating of 3 kW. When it is used, some energy is transferred usefully to the water and some energy is wasted.

## Mark scheme (4 marks)

1. Some energy is transferred to the surroundings / to the air / as heat from the outer casing of the kettle
2. This is a waste energy transfer / this energy does not directly serve the purpose of the kettle
3. Conservation of energy means energy cannot be created or destroyed, so the useful output energy transfer cannot exceed the total energy input
4. Therefore efficiency is less than 1 (or 100%) because useful output energy transfer is less than total energy input

## Key terms

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

## 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-electric-kettle-is-used-to-88279c6c) · Published by Druglandscape Ltd.