# A mobile phone battery transfers energy to the phone's components. Explain why the total energy supplied by the battery is greater than the useful energy transferred to the screen and processor, and describe one way the efficiency of the phone's energy use could be improved.

> Edexcel A-Level Physics (9PH0) — 3.1 Charge and current · Explain · 5 marks

> A mobile phone uses a rechargeable battery. When the phone is in use, the screen displays images, the processor carries out calculations, and the casing becomes warm to the touch.

## Mark scheme (5 marks)

1. The phone produces waste energy transfer (in the form of heat/thermal energy)
2. By the law of conservation of energy, energy cannot be created or destroyed, so the total input must account for both useful and waste outputs
3. The useful energy transferred is only the energy that directly serves the purpose of the device (powering the screen and processor)
4. Efficiency = useful energy transferred by the device ÷ total energy supplied to the device, so because waste energy is produced, efficiency is less than 1 (or 100%)
5. One valid method to improve efficiency, e.g. thermal insulation to reduce heat lost to surroundings / reducing friction in moving parts via lubrication / recycling waste heat energy as a useful input

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-mobile-phone-battery-transfers-energy-74bc6db3) · Published by Druglandscape Ltd.