Question

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 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 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.

Answer 1

(a) The metal detector works on the principle of resonance in 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 walk through the metal in her pocket, the impedance of the circuit changes-resulting in significant 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.