# A student discovers that the plastic casing of an electric kettle has become cracked, exposing the metal heating element inside. Explain why touching the exposed metal could be dangerous, and describe two safety features built into the mains electrical system that are designed to protect the user in such a situation.

> Cambridge International IGCSE Physics (0625) — 4.4 Electrical safety · Explain and Describe · 4 marks

## Mark scheme (4 marks)

1. The exposed metal could become live (connected to the live wire) / at a high potential difference relative to earth, so a current could pass through the person's body to earth, causing an electric shock.
2. The earth wire (green and yellow) connects the metal casing to earth so that if the casing becomes live, current flows safely to earth rather than through the user.
3. The large fault current that flows through the earth wire causes the fuse to melt / blow, breaking the circuit and cutting off the current.
4. A residual current circuit breaker (RCCB) detects a difference in current between the live and neutral wires and switches off / trips the circuit very quickly, protecting the user.

## Related

- [Revision notes for Cambridge International IGCSE Physics (0625)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain and Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-discovers-that-the-plastic-f73f3e52) · Published by Druglandscape Ltd.