Q1. [3] medium thorough-understanding
In a domestic circuit, the earth wire does not carry current during normal operation, yet it is considered a critical safety component. Using your understanding of both domestic wiring and the behaviour of current-carrying conductors, explain what happens inside a faulty appliance whose metallic body becomes live, and how the earth wire prevents a dangerous electric shock.
Generated by claude-sonnet-4-6 · 2026-06-26 01:13 · grounding rag
Model Answer
In a faulty appliance, the insulation inside breaks down, causing the live wire (220 V) to come in contact with the metallic body. The body becomes live and carries current at high potential.
The earth wire connects this metallic body to a metal plate buried deep in the earth. Since earth is at zero potential, it provides a low-resistance path for the leakage current to flow safely into the ground. This prevents the body's potential from rising above earth potential. So, if a person touches the appliance, no dangerous current passes through them and they are protected from severe electric shock.
Source: Chapter 12, Section 12.4 — Domestic Electric Circuits
---
Explanation
- 3 marks → 3 clear points: (1) How the body becomes live, (2) what the earth wire does physically (low-resistance path to earth), (3) why this prevents shock (potential stays at earth level).
- Examiners look for the phrase "low-resistance conducting path" — use it exactly.
- Mention that earth potential = 0 V to explain why current flows through the earth wire rather than through the user.
- Don't confuse the role of the fuse (protects the circuit from overloading) with the earth wire (protects the user from shock) — keep them distinct here.