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In the given figure a metallic plate A is allowed to swing like a simple pendulum between the magnetic poles and it comes to rest after time t. If a slot is cut in the plate A and then it is allowed to swing with the same initial velocity as before then the time taken by it to come to rest will be:

In the given figure a metallic plate A is allowed to swing like a simple pendulum between the magnetic poles and it comes to rest after time t. If a slot is cut in the plate A and then it is allowed to swing with the same initial velocity as before then the time taken by it to come to rest will be: Correct Answer More than t

CONCEPT:

Eddy current:

  • When a changing magnetic flux is applied to a bulk piece of conducting material then circulating currents called eddy currents are induced in the material.
  • Because the resistance of the bulk conductor is usually low, eddy currents often have large magnitudes and heat up the conductor.
  • These are circulating currents like eddies in the water.
  • The experimental concept was given by Focault hence also named “Focault current”.
  • The production of eddy currents in a metallic block leads to the loss of electric energy in the form of heat.
  • Eddy currents are undesirable in the metallic cores of transformers, electric motors, and other such devices in which a coil is to be wound over a metallic core since they heat up the core and dissipate electrical energy in the form of heat.
  • Eddy currents are minimized by using laminations of metal to make a metal core. The laminations are separated by an insulating material like lacquer.
  • Eddy currents are used to advantage in certain applications like:
    1. Magnetic braking in trains
    2. Electromagnetic damping
    3. Induction furnace
    4. Electric power meters

EXPLANATION:

  • In the given figure when the metallic plate A is allowed to swing like a simple pendulum between the magnetic poles, the magnetic flux associated with the plate keeps on changing as the plate moves in and out of the region between magnetic poles.
  • Due to this changing magnetic flux, the eddy currents induced in the plate oppose the motion of the plate.
  • If a slot is cut in plate A area then the area available to the flow of eddy currents is less. Thus, the pendulum plate with holes or slots reduces electromagnetic damping, and the plate swings more freely.
  • Therefore the times taken to by the plate to come to rest will increase when a slot is cut in the plate. Hence, option 1 is correct.

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