A student notices that the cable connecting a lamp to the mains socket has become frayed, exposing the live wire inside. Explain why touching the exposed live wire is dangerous, and describe the role of the circuit breaker in protecting the student if a fault occurs.

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)

The live wire carries the mains voltage of about 230 V AC. If it is touched, the current can flow through the body to earth, producing an electric shock. A fault that draws a large current will trip the circuit breaker, which detects the over‑current and opens the circuit, stopping the flow of electricity. The breaker can then be reset and used again, unlike a fuse.

Examiner tips

  • Use the exact voltage value (230 V) and mention AC; explain shock via body to earth; state over‑current detection and opening of circuit; note resetability of breaker

Common mistakes

  • Saying the wire is dangerous because it is hot rather than because of voltage; confusing a fuse with a circuit breaker; omitting that the breaker opens the circuit to stop current flow

Mark scheme (4 marks)

  1. The live wire is at a high (alternating) voltage / 230 V
  2. Touching the live wire allows current to flow through the body to earth, causing an electric shock
  3. If a fault causes too large a current, the circuit breaker detects this and switches the circuit off / breaks the circuit
  4. The circuit breaker can be reset and used again, making it more convenient than a fuse

Key terms in this question

live wire · circuit breaker

Related

More Domestic uses and safety questions

▶ Try answering this question with AI marking (free) →