# A student is investigating ways to improve the efficiency of a model electric motor used to lift a small mass. The motor wastes energy as heat due to friction in its moving parts, and also loses energy as sound. Explain how the efficiency of the motor can be increased, and describe what effect this would have on the useful energy transferred by the motor.

> Edexcel A-Level Physics (9PH0) — 3.2 EMF, resistance and circuits · Explain · 5 marks

> A model electric motor is supplied with 200 J of electrical energy. It transfers 80 J of energy as useful work lifting a mass. The remaining energy is wasted as heat and sound.

## Mark scheme (5 marks)

1. Efficiency is the ratio of useful output energy to total input energy
2. Lubrication of the moving parts reduces friction
3. Reducing friction means less energy is wasted as heat
4. Reducing waste energy increases the efficiency of the motor
5. More of the total input energy is transferred as useful energy (lifting the mass), so the useful energy transferred increases

## Key terms

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

## 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-student-is-investigating-ways-to-49f8dd82) · Published by Druglandscape Ltd.