A hairdryer has a plastic casing and is connected to the mains supply using a two-core cable containing a live wire and a neutral wire. Explain why a hairdryer with a plastic casing does not need an earth wire, and explain the role of the fuse inside the hairdryer's plug.

Eduqas GCSE Physics — 7.4 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 plastic casing is an electrical insulator and does not conduct electricity. Therefore the outer shell of the hairdryer cannot become live and touching it does not pose a risk of electrocution. The fuse inside the plug is a safety device that melts when the current exceeds its rating. It breaks the circuit, protecting the appliance, the wiring and preventing fire or damage caused by a large current.

Examiner tips

  • Use the word ‘insulator’ to show understanding of plastic’s properties.
  • Explain that the fuse ‘melts’ or ‘breaks the circuit’ when over‑current occurs.
  • Show that the fuse protects the appliance, wiring and fire risk.

Common mistakes

  • Claiming the plastic is a conductor, or that the casing must be earthed.
  • Forgetting to mention that the fuse protects against over‑current and fire.
  • Using vague terms like ‘safety’ without specifying the fuse’s function.

Mark scheme (4 marks)

  1. Plastic is an electrical insulator / does not conduct electricity
  2. So the casing cannot become live / there is no risk of electrocution if the casing is touched
  3. The fuse melts / breaks the circuit if the current exceeds the fuse rating
  4. This protects the appliance / wiring / prevents fire / prevents damage caused by a large current

Key terms in this question

live wire · neutral wire · fuse · earth wire

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