# A tumble dryer has a power-rating of 2.5 kW. It is used for 2 hours each day. Explain how a consumer could use the power-rating and the time of use to work out the cost of running the tumble dryer, and why electricity companies use the kilowatt-hour rather than the joule for billing domestic customers.

> Eduqas GCSE Physics — 1.4 Domestic electricity · Explain · 4 marks

> Electricity companies charge domestic customers based on the number of kilowatt-hours of energy they use each month.

## Mark scheme (4 marks)

1. The energy used is found by multiplying the power-rating (in kilowatts) by the time used (in hours)
2. This gives the number of kilowatt-hours consumed, which is then multiplied by the cost per kilowatt-hour to find the total cost
3. Domestic energy consumption is very large, so the joule is an inconveniently small unit
4. The kilowatt-hour gives more manageable/convenient numbers for billing domestic customers

## Key terms

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

## 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-tumble-dryer-has-a-power-rating-6e832385) · Published by Druglandscape Ltd.