# A solar-powered water pump is used to move water from a river to a storage tank. The pump has a power rating of 500 W but only transfers 300 W as useful energy to the water. Explain what is meant by 'useful energy transfer' and 'waste energy transfer' in this context, and describe how the efficiency of the pump could be improved.

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

> A solar-powered water pump transfers energy from sunlight to raise water from a river to a storage tank. Not all of the energy input is transferred usefully.

## Mark scheme (4 marks)

1. Useful energy transfer is the transfer of energy that directly serves the purpose of the system — here, moving/raising the water (gravitational potential energy).
2. Waste energy transfer is the transfer of energy to a form that does not directly serve the purpose of the system — here, energy lost as heat/sound due to friction in the pump motor.
3. Lubrication of moving parts in the pump reduces friction, reducing waste (thermal) energy transfer and improving efficiency.
4. Efficiency can never exceed 1 (or 100%) because energy is conserved — it can only be transferred or dissipated, not created; so the useful output can never exceed the total input.

## 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)
- [efficiency](https://www.gradenine.co.uk/glossary/efficiency)

## 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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Source: [GradeNine](https://www.gradenine.co.uk/q/a-solar-powered-water-pump-is-used-b9c1ab6b) · Published by Druglandscape Ltd.