Q1. [1] medium thorough-understanding
Which of the following correctly describes what happens inside a fuse wire when a short circuit occurs?
(A) The fuse wire increases its resistance, reducing the current to a safe level.
(B) The high current causes Joule heating in the fuse wire, melting it and breaking the circuit.
(C) The fuse wire deflects the excess current to the earth wire, protecting the appliance.
(D) The fuse wire expands and disconnects the live wire from the neutral wire mechanically.
- A The fuse wire increases its resistance, reducing the current to a safe level.
- B The high current causes Joule heating in the fuse wire, melting it and breaking the circuit.
- C The fuse wire deflects the excess current to the earth wire, protecting the appliance.
- D The fuse wire expands and disconnects the live wire from the neutral wire mechanically.
Generated by claude-sonnet-4-6 · 2026-06-26 01:12 · grounding rag
Model Answer
(B) The high current causes Joule heating in the fuse wire, melting it and breaking the circuit.
Explanation
The textbook (Section 12.4) explicitly states: "The Joule heating that takes place in the fuse melts it to break the electric circuit." During a short circuit, current increases abruptly; the fuse wire, having a low melting point, melts due to this Joule heating, thus breaking the circuit. Options A, C, and D describe mechanisms not associated with fuse operation.