A laptop computer is connected to the mains electricity supply whilst being used to play a video. Explain why the laptop is not 100% efficient, and describe one way in which the efficiency of the laptop could be improved.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A laptop transfers electrical energy from the mains supply. Its fan runs continuously to prevent overheating during use.
Model answer (4 marks)
1. The mains supply delivers electrical energy to the laptop.
2. Inside the laptop, part of this energy is converted into useful work (display, processor, etc.) and part is lost as waste energy.
3. The waste energy is mainly heat, which is transferred to the surroundings by the components and the fan.
4. Because some energy is lost as heat, the useful output is less than the input, so the efficiency is less than 100 %.
5. Efficiency could be improved by using components that generate less heat (e.g. lower‑resistance chips) or by improving the fan’s operation, such as better lubrication to reduce friction and heat generation.
2. Inside the laptop, part of this energy is converted into useful work (display, processor, etc.) and part is lost as waste energy.
3. The waste energy is mainly heat, which is transferred to the surroundings by the components and the fan.
4. Because some energy is lost as heat, the useful output is less than the input, so the efficiency is less than 100 %.
5. Efficiency could be improved by using components that generate less heat (e.g. lower‑resistance chips) or by improving the fan’s operation, such as better lubrication to reduce friction and heat generation.
Examiner tips
- Use the word ‘waste energy’ and give a specific example (heat).
- Explain the conservation of energy link to efficiency <100 %.
- Mention a realistic improvement such as lower‑resistance components or better fan lubrication.
Mark scheme (4 marks)
- The laptop produces waste energy transfer(s) / not all energy transferred is useful
- Named waste energy transfer — e.g. thermal/heat energy transferred to surroundings (from the components/fan)
- Conservation of energy means total energy output equals total energy input, so if some is wasted the useful output must be less than the input / efficiency cannot exceed 1 (100%)
- Efficiency could be improved by lubrication (of moving parts / fan) OR by using components that produce less waste thermal energy (e.g. lower-resistance components) — reducing waste energy transfer
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
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