# Sunita and her friends visited an exhibition . The policeman asked them to pass through a metal detector. Sunita's friends were initially scared of it. Sunita, however, explained to them the purpose - Physics

Short Note

Sunita and her friends visited the exhibition. The policeman asked them to pass through a metal detector. Sunita's friends were initially scared of it. Sunita, however, explained to them the purpose and working of the metal detector.

(a) On what principle does a metal detector work?
(b) Why does the detector emit a sound when a person carrying any metallic object walks through it?
(c) State any two qualities which Sunita displayed while explaining the purpose of walking through the detector.

#### Solution

(a) The metal detector works on the principle of resonance in the ac circuit.

(b) When Sunita's friend is passed through a metal detector, her friend, in fact, passing through a coil of many turns. The coil is connected to a capacitor tuned so that the circuit is in resonance. When she walked through the metal in her pocket, the impedance of the circuit changes-resulting insignificant change in current in the circuit. The change in current is detected and the electric circuitry causes a sound to be emitted as an alarm.

(c) Curiosity, power of observation.

Concept: Flow of Electric Charges in a Metallic Conductor
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