# A student uses an electric hair dryer to dry their hair. The hair dryer produces warm moving air, but the outer casing also becomes hot during use. Explain why the hair dryer cannot have an efficiency of 1 (100%), and describe one way in which the efficiency of electrical appliances like the hair dryer could be increased.

> OCR GCSE Physics A: Gateway Science (J249) — P7 Energy · Explain · 4 marks

> An electric hair dryer transfers electrical energy to produce a warm, fast-moving airstream. Its purpose is to dry hair by directing warm air onto it. After several minutes of use, the plastic casing of the hair dryer feels noticeably warm to the touch.

## Mark scheme (4 marks)

1. The useful energy transfer is the warm moving air (kinetic and thermal energy of the air) directed at the hair
2. The heating of the casing is a waste energy transfer — energy is dissipated to the surroundings as heat and does not serve the purpose of the appliance
3. Because of the conservation of energy, total energy input always equals useful output plus waste energy transfer, so efficiency (useful output ÷ total input) must always be less than 1
4. Efficiency can be increased by reducing the current in the wires (which reduces heating of wires / reduces power loss due to resistance), OR by using lubrication on moving parts to reduce friction and heat loss

## Key terms

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

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](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-student-uses-an-electric-hair-189f40f9) · Published by Druglandscape Ltd.