A tumble dryer spins wet clothes inside a drum while blowing hot air through them. Explain how energy is usefully transferred and wasted during this process, and state one way in which the efficiency of the tumble dryer could be improved.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Electrical energy from the mains is converted into kinetic energy to spin the drum and into thermal energy to heat the air. The kinetic energy helps tumble the clothes, while the heat evaporates moisture. Some of the electrical energy is lost as waste heat to the surrounding air and as sound. The waste heat is mainly produced by friction between the drum and its bearings and by the motor’s internal resistance. To improve efficiency, the dryer could be lubricated to reduce bearing friction or better insulated to minimise heat loss to the surroundings.
Examiner tips
- Use the exact terms ‘electrical’, ‘kinetic’, ‘thermal’, ‘friction’, ‘lubrication’, ‘insulation’
- Show the link between friction and waste heat
- Give one specific improvement method
Common mistakes
- Confusing heat loss with useful heat transfer
- Failing to mention friction as the source of waste heat
- Suggesting a change that does not affect energy transfer, e.g. changing the colour of the drum
Mark scheme (4 marks)
- Useful energy transfer identified — electrical energy is usefully transferred to kinetic energy (to spin the drum) and/or thermal/heat energy (to dry the clothes)
- Waste energy transfer identified — energy is dissipated as heat to the surroundings and/or sound that does not directly serve the purpose of the dryer
- Waste transfer linked to friction between moving parts / bearings / drum
- Valid method of improving efficiency stated — lubrication of moving parts to reduce friction, OR improved thermal insulation to reduce heat loss to surroundings
Key terms in this question
Related
- All WJEC GCSE Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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