A student plugs a metal-cased electric kettle into a mains socket. Explain why a fuse is used in the plug of the kettle and describe what happens inside the fuse if a fault causes a very large current to flow.

AQA GCSE Physics (8463) — 4.2.3 Domestic uses and safety · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

A fuse contains a thin fuse wire that melts when the current exceeds a safe level.
The melting of the wire breaks the circuit, stopping current from flowing.
This prevents the kettle, its wiring or the mains cable from overheating and potentially causing a fire.
The large current heats the fuse wire so much that it reaches its melting point and breaks apart.

Examiner tips

  • Use the word "melts" or "breaks" for the fuse action. Mention that the fuse protects the appliance and the mains wiring. Show the cause–effect chain: high current → heating → melting → circuit break.
  • Include the safety outcome (prevents overheating and fire).

Common mistakes

  • Writing that the fuse simply 'shuts off' without explaining melting. Forgetting to mention the protection of the appliance or wiring. Using vague terms like "overheats" without linking to the fuse wire melting.

Mark scheme (4 marks)

  1. The fuse contains a thin wire (fuse wire) that melts / breaks when the current exceeds a safe level
  2. This breaks / disconnects the circuit (stopping current from flowing)
  3. This prevents the appliance / wiring / cable from overheating (which could cause a fire)
  4. The large current causes the fuse wire to heat up enough to melt (because the heating effect of the current is large)

Key terms in this question

fuse · current

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