A light disc made of aluminium (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) [2020]

Question

Smart Achievers · Accepted Answer

(2)

Due to motion of magnet above the disc, the plate moves through the magnetic flux, due to which an EMF is generated in the plate and eddy currents are induced. These currents are such that it opposes the relative motion so disc will rotate in the same direction as the direction of magnet's motion.

This apparatus is called Arago's disc and the effect was discovered in 1824 by Arago.

Solution

1 rotate in the direction opposite to the direction of magnet's motion

2 rotate in the same direction as the direction of magnet's motion

3 not rotate and its temperature will remain unchanged

4 not rotate but its temperature will slowly rise

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