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Alternating Current question

2022 · 25 Jul · Shift 2 · Q54
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Alternating Current question

2022 · 25 Jul · Shift 2 · Q54

JEE MainPhysicsAlternating CurrentMCQ+4 / −1
When you walk through a metal detector carrying a metal object in your pocket, it raises an alarm. This phenomenon works on :
  1. A
    Electromagnetic induction
  2. B
    Resonance in ac circuits
  3. C
    Mutual induction in ac circuits
  4. D
    Interference of electromagnetic waves
View written solutionFree

Correct answer: A

  1. Identify the working principle of a metal detector

    A walk-through metal detector contains coils carrying alternating current. This produces a time-varying magnetic field.

  2. What happens when a metal object enters this field?

    When a metal object is brought into a changing magnetic field, eddy currents are induced in the metal.

    This is due to Faraday’s law of electromagnetic induction.

  3. Effect of these induced currents

    The induced currents produce their own magnetic field, which changes the impedance/signals in the detector coil circuit. The electronic system senses this change and triggers the alarm.

  4. Check the options

    • A: Electromagnetic induction — Correct. The detection is based on induced currents in the metal object due to changing magnetic field.
    • B: Resonance in ac circuits — Not the fundamental principle for detecting the metal object.
    • C: Mutual induction in ac circuits — Not the primary principle here; the metal object is not acting as a normal secondary coil. The key effect is induction of eddy currents.
    • D: Interference of electromagnetic waves — Incorrect.

  5. Conclusion

    Therefore, the phenomenon works on electromagnetic induction.

A: Electromagnetic induction\boxed{\text{A: Electromagnetic induction}}A: Electromagnetic induction​

  1. Comparison with stored correct answer

    Stored correct answer: B

    Derived answer: A

    These do not match. The usual physics principle of metal detectors is electromagnetic induction via eddy currents, so the stored answer appears incorrect.

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