A vacuum cleaner and a filament lamp are both connected to the mains electricity supply. Describe the useful and wasted energy transfers that occur in each appliance, and state which appliance you would expect to have the higher power rating. Justify your answer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
A vacuum cleaner:
1. Usefully transfers electrical energy to kinetic energy – the motor turns the fan and the brush, moving air.
2. Wastes energy as heat (from the motor and wiring) and sound.
A filament lamp:
1. Usefully transfers electrical energy to light energy – the filament emits visible light.
2. Wastes most of the energy as heat (the filament and surrounding parts become hot).
The vacuum cleaner has the higher power rating because it needs to supply more energy per second to run its motor and move air, whereas the lamp only needs enough power to produce light.
1. Usefully transfers electrical energy to kinetic energy – the motor turns the fan and the brush, moving air.
2. Wastes energy as heat (from the motor and wiring) and sound.
A filament lamp:
1. Usefully transfers electrical energy to light energy – the filament emits visible light.
2. Wastes most of the energy as heat (the filament and surrounding parts become hot).
The vacuum cleaner has the higher power rating because it needs to supply more energy per second to run its motor and move air, whereas the lamp only needs enough power to produce light.
Examiner tips
- Use the word ‘useful’ and ‘wasted’ clearly; list the energy forms for each appliance.
- Show the comparison of power ratings by stating that the vacuum cleaner requires more energy per second.
- Mention heat as the main waste in both devices.
- Keep the answer concise and to the point.
Common mistakes
- Confusing heat with light as the useful output of the lamp.
- Failing to state that the vacuum cleaner’s power rating is higher.
- Not distinguishing between kinetic and thermal energy in the vacuum cleaner.
Mark scheme (4 marks)
- A vacuum cleaner usefully transfers electrical energy to kinetic energy (to move air/spin the motor).
- A filament lamp usefully transfers electrical energy to light energy, but wastes (the majority of) energy as thermal energy / heat.
- Both appliances waste some energy as thermal energy (vacuum cleaner wastes energy as heat/sound; filament lamp wastes energy as heat).
- The vacuum cleaner has the higher power rating because it transfers more energy per second / requires more energy to operate its motor than the lamp requires to produce light.
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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