Question

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

• A. Change in reluctance of an iron core in presence of a metallic object
• B. Change in conductance of an iron core in presence of a metallic object
• C. Electric field induced by a metallic object
• D. Eddy current generation in a metallic object

Hint:

Eddy currents are loops of electric current induced in conductors by changing magnetic fields. Devices like metal detectors rely on detecting these currents.

Answer 1

The Correct Option is D

Step 1: Understand the mechanism of metal detectors.
Hand-held metal detectors operate on the principle of electromagnetic induction. When the device is moved over a metallic object, it induces eddy currents in the metal.

Step 2: Effect of eddy currents.
These eddy currents generate their own magnetic field, which interferes with the original magnetic field of the detector’s coil. This interference is detected as a change, indicating the presence of metal.

Step 3: Conclusion.
This is not about changes in reluctance or conductance, nor electric fields. It's based on magnetic field disturbance due to eddy currents.