# A student plugs a laptop charger into the mains supply at home. The cable connecting the charger to the plug contains three wires: a live wire, a neutral wire, and an earth wire. Explain the role of each wire and describe how the earth wire, together with the fuse, protects the user if the live wire accidentally touches the metal casing of the charger.

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

## Mark scheme (4 marks)

1. The live wire carries the alternating current / high-voltage supply to the appliance
2. The neutral wire completes the circuit / returns current back to the supply at approximately 0 V
3. If the live wire touches the metal casing, the earth wire provides a low-resistance path to earth, so a large current flows through the earth wire
4. The large fault current melts / blows the fuse, breaking the circuit and making the casing safe / preventing electrocution

## Key terms

- [live wire](https://www.gradenine.co.uk/glossary/live-wire)
- [neutral wire](https://www.gradenine.co.uk/glossary/neutral-wire)
- [earth wire](https://www.gradenine.co.uk/glossary/earth-wire)
- [fuse](https://www.gradenine.co.uk/glossary/fuse)

## Related

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

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-plugs-a-laptop-charger-a24d443c) · Published by Druglandscape Ltd.