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JEE MainPhysicsAlternating Current

A metal detector at an airport operates using an LC oscillator circuit tuned to a specific resonant frequency. When a passenger carrying a metallic object walks through the detector, the alarm is triggered because the circuit is thrown out of resonance. Which parameter of the circuit primarily changes due to the presence of the metallic object, causing this shift in the resonant frequency?

Options

  1. AThe capacitance of the tuning circuit changes
  2. BThe frequency of the AC voltage source changes
  3. CThe inductance of the search coil changes
  4. DThe resistance of the circuit drops to zero

Correct answer

C. The inductance of the search coil changes

Step-by-step solution

A metal detector operates using an LC oscillator circuit that is tuned to a specific resonant frequency. The search coil of the detector acts as the inductor in this circuit. When a metallic object enters the magnetic field of the search coil, it induces eddy currents in the metal (or alters the magnetic permeability of the core region), which changes the effective inductance of the coil. Since the resonant frequency is given by f = 1 2 LC , this change in inductance shifts the resonant frequency, throwing the circ

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