A washing machine transfers electrical energy to wash clothes. Describe the useful energy transfer and the waste energy transfer that occur when the washing machine is in use, and explain one way in which the efficiency of the washing machine could be improved.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A washing machine uses an electric motor to spin a drum. As the drum spins, it gets warm and produces a humming sound.
Model answer (4 marks)
The washing machine converts electrical energy from the mains into useful kinetic energy when the motor turns the drum, which agitates the clothes.
The waste energy is mainly thermal energy, as the motor and drum become warm, and acoustic energy, the humming sound, both of which do not help wash the clothes.
Efficiency could be improved by reducing friction in the motor and drum bearings – for example, by better lubrication – which lowers the amount of electrical energy lost as heat and sound, so a larger fraction of the input energy becomes useful kinetic energy.
The waste energy is mainly thermal energy, as the motor and drum become warm, and acoustic energy, the humming sound, both of which do not help wash the clothes.
Efficiency could be improved by reducing friction in the motor and drum bearings – for example, by better lubrication – which lowers the amount of electrical energy lost as heat and sound, so a larger fraction of the input energy becomes useful kinetic energy.
Examiner tips
- Use the exact terms ‘electrical energy’, ‘kinetic energy’, ‘thermal energy’ and ‘acoustic energy’.
- Explain the improvement in terms of reducing friction and increasing the proportion of useful energy.
- Show the cause–effect link between reduced friction and higher efficiency.
Common mistakes
- Confusing the drum’s kinetic energy with the clothes’ kinetic energy.
- Mentioning only heat as waste energy and ignoring sound.
Mark scheme (4 marks)
- The useful energy transfer is electrical energy transferred to kinetic energy (of the spinning drum / motor).
- Waste energy transfers include thermal (heat) energy and/or sound energy, which do not directly serve the purpose of the machine.
- Lubrication of the moving parts (motor/drum bearings) reduces friction between surfaces.
- Reducing friction means less waste energy transfer (as heat/sound), so a greater proportion of the input energy is usefully transferred, increasing efficiency.
Key terms in this question
useful energy transfer · waste energy transfer · efficiency
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
More Making use of energy questions
- A student uses an electric fan heater to warm a room. Explain why the efficiency…
- A cyclist wants to improve the efficiency of their bicycle. Explain how lubricat…
- A student places a hot drink in a polystyrene cup and notices it stays warm for …
- A student uses an electric toaster to make toast. The toaster has a power-rating…