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JEE Advanced Physics Electromagnetic Induction 2020 JEE Advanced 2020 (Paper 1)

JEE Advanced Physics Question (2020) — Solution

Question

A light disc made of aluminum (a nonmagnetic material) is kept horizontally and is free to rotate about its axis as shown in the figure. A strong magnet is held vertically at a point above the disc away from its axis. On revolving the magnet about the axis of the disc, the disc will (figure is schematic and not drawn to scale)

Options

  1. A. rotate in the direction opposite to the direction of magnet's motion
  2. B. rotate in the same direction as the direction of magnet's motion
  3. C. not rotate and its temperature will remain unchanged
  4. D. not rotate but its temperature will slowly rise

Answer

B. rotate in the same direction as the direction of magnet's motion

Step-by-step solution

When we start rotating the magnet above the disc, eddy currents will be generated in the disc. Now we know from Lenz's law that the induced emf will drive the current such that it opposes the cause of the production of induced emf. Hence the disc will rotate in the same direction as the direction of magnet's motion

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