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.
Answer the following questions :
(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.
(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.