Describe the role of the live wire and the neutral wire in a mains electricity supply, and explain why the live wire can be dangerous even when an appliance is switched off.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The live wire carries the alternating potential difference from the mains supply (≈230 V). The neutral wire provides the return path and is at approximately 0 V. Even when the appliance switch is open, the live wire remains connected to the supply and therefore stays at 230 V. If a person touches the live wire, current can flow through the body to earth, producing an electric shock.
Examiner tips
- Use the exact terms "live" and "neutral" and state their voltages. Mention the return path for neutral. Explain that the live stays live when switched off. Show the shock mechanism.
Common mistakes
- Confusing live with neutral or vice‑versa. Assuming the live wire is de‑energised when the appliance is off. Omitting the 230 V figure or the 0 V reference for neutral.
Mark scheme (4 marks)
- The live wire carries the alternating potential difference from the supply (at 230 V).
- The neutral wire completes the circuit (at 0 V).
- The live wire remains at 230 V / is still connected to the supply even when the switch is open / appliance is off.
- If a person touches the live wire, current flows through them to earth, causing an electric shock.
Key terms in this question
live wire · neutral wire · mains electricity
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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