# A solar-powered water pump is used to raise water from a well. The pump has a useful energy output of 1 200 J and a total energy input of 5 000 J. Describe what is meant by useful energy transfer and waste energy transfer in this context, and explain why the total energy in the system is still conserved despite waste energy being produced.

> Pearson Edexcel International GCSE Physics (4PH1) — 4.1 Energy transfers · Describe · 4 marks

> A solar-powered water pump converts energy from sunlight to raise water from a well. For every 5 000 J of energy supplied to the pump, 1 200 J 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, the energy transferred to gravitational potential energy of the raised water.
2. Waste energy transfer is the transfer of energy to a form that does not directly serve the purpose of the system — for example, thermal energy lost to the surroundings due to friction in the pump.
3. Energy is conserved because it is never created or destroyed; it is only transferred from one store to another.
4. The waste energy (thermal/heat energy dissipated to the surroundings) plus the useful energy output together equal the total energy input of 5 000 J, so no energy is lost overall.

## 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)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-solar-powered-water-pump-is-used-d8ee5a84) · Published by Druglandscape Ltd.