A tumble dryer transfers electrical energy to dry clothes. Not all of the electrical energy is usefully transferred. Explain what happens to the wasted energy in the tumble dryer and describe one way the efficiency of the tumble dryer could be increased.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The electrical energy supplied to the dryer is converted into heat and mechanical energy. A large part of this energy is lost as heat to the surrounding air and to the dryer’s metal frame, so it is dissipated as thermal energy in the environment. Energy is conserved – the lost energy is still present, just not useful for drying.
The efficiency can be raised by reducing this waste. For example, adding better thermal insulation around the drum and heating elements keeps more heat inside the dryer, or using a heat‑recovery system to recycle the waste heat back into the drying cycle.
The efficiency can be raised by reducing this waste. For example, adding better thermal insulation around the drum and heating elements keeps more heat inside the dryer, or using a heat‑recovery system to recycle the waste heat back into the drying cycle.
Examiner tips
- Use the word ‘dissipated’ or ‘lost as heat’ to show understanding of energy loss. Show that energy is conserved – the lost energy is still present. Give a specific method to reduce waste, e.g. insulation or heat‑recovery. Link the method to an increase in the useful output/total input ratio.
Common mistakes
- Saying the energy is ‘destroyed’ instead of ‘dissipated’. Failing to mention that energy is still present in the surroundings. Giving a method that does not actually reduce waste heat, such as changing the drum speed without insulation.
Mark scheme (4 marks)
- The wasted energy is dissipated to the surroundings / transferred to thermal energy store of the surroundings
- The total energy is conserved / energy cannot be created or destroyed
- Efficiency can be increased by reducing waste energy, e.g. by using lubrication / thermal insulation / recycling waste thermal energy back into the system
- Reducing waste energy means a greater proportion of the total energy input is usefully transferred / the ratio of useful output to total input increases
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →