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At an airport, a person is made to walk through the doorway of a metal detector, for security reasons. If she/he is carrying anything made of metal, the metal detector emits a sound. On what principle does this detector work? Ans : The metal detector works on the principle of resonance in ac circuits. When you walk through a metal detector, you are, in fact, walking through a coil of many turns. The coil is connected to a capacitor tuned so that the circuit is in resonance. When you walk through with metal in your pocket, the impedance of the circuit changes – resulting in significant change in current in the circuit. This change in current is detected and the electronic circuitry causes a sound to be emitted as an alarm. How does this impedance changes

At an airport, a person is made to walk through the doorway of a metal detector, for security reasons. If she/he is carrying anything made of metal, the metal detector emits a sound. On what principle does this detector work?
Ans : The metal detector works on the principle of resonance in ac circuits. When you walk through a metal detector, you are, in fact, walking through a coil of many turns. The coil is connected to a capacitor tuned so that the circuit is in resonance. When you walk through with metal in your pocket, the impedance of the
circuit changes – resulting in significant change in current in the circuit. This change in current is detected and the electronic circuitry causes a sound to be emitted as an alarm.
How does this impedance changes

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1 Answers

Vikas TU
14149 Points
3 years ago
Metal detector works on the principle of magnetic induction.
There is a transmitter coil around the doorway and powered by a current so the region inside the doorway is a magnetic region.
When a metallic object move in the magnetic region of the doorway then it feels a magnetic field of the transmitter coil  so  it also generate  a magnetic field. This field is  called secondary magnetic field and here comes the role of receiver coil in the doorway which detects the secondary field by the metal and current flows through the receiver coil when it feels secondary field and thus enabling the alarm connected to receiver coil to emit a sound.

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