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Electromagnetic Induction question

2023 · 8 Apr · Shift 1 · Q50
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Electromagnetic Induction question

2023 · 8 Apr · Shift 1 · Q50

JEE MainPhysicsElectromagnetic InductionMCQ+4 / −1
Certain galvanometers have a fixed core made of non magnetic metallic material. The function of this metallic material is
  1. A
    to bring the coil to rest quickly
  2. B
    to produce large deflecting torque on the coil
  3. C
    to oscillate the coil in magnetic field for longer period of time
  4. D
    to make the magnetic field radial
View written solutionFree

Correct answer: A

  1. Identify the role of the fixed core in a galvanometer

    In certain galvanometers, a fixed core of non-magnetic metallic material is provided inside the coil.

  2. Effect of a non-magnetic metallic core

    Since the material is metallic, when the coil moves in the magnetic field, eddy currents are induced in the metallic core.

    By Lenz's law, these eddy currents oppose the motion causing them.

  3. Purpose of eddy current damping

    The opposing effect of eddy currents produces damping torque, which helps the moving coil:

    • stop oscillating quickly,
    • come to rest faster,
    • give a steady reading sooner.

  4. Check the options

    • A: to bring the coil to rest quickly
      Correct. This is exactly the purpose of damping by eddy currents.

    • B: to produce large deflecting torque on the coil
      Incorrect. Deflecting torque depends on magnetic field, current, number of turns, and coil area, not on this non-magnetic metallic core.

    • C: to oscillate the coil in magnetic field for longer period of time
      Incorrect. Damping reduces oscillations; it does not prolong them.

    • D: to make the magnetic field radial
      Incorrect. A soft iron core is used to make the magnetic field radial, not a non-magnetic metallic core.

  5. Conclusion

    Therefore, the metallic core is used for eddy current damping, so that the coil comes to rest quickly.

Option A\boxed{\text{Option A}}Option A​

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