The GATE Grind

GATE 2025 IN – Question 13

Sensors and Industrial Instrumentation · Piezoelectric electromagnetic and Hall sensors · 1 mark · Multiple choice

The working of the hand-held metal detector most widely used by security personnel for human frisking is based on the principle of

  1. change in reluctance of an iron core in presence of a metallic object
  2. change in conductance of an iron core in presence of a metallic object
  3. electric field induced by a metallic object
  4. eddy current generation in a metallic object

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (D) eddy current generation in a metallic object

Explanation

An alternating magnetic field induces eddy currents in a nearby conducting object.

Their secondary field changes the detector-coil response, revealing metal even when it is nonferromagnetic.

Thus **eddy-current generation, D** is the operating principle.