Question

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)

• A. rotate in the direction opposite to the direction of magnet’s motion
• B. rotate in the same direction as the direction of magnet’s motion
• C. not rotate and its temperature will remain unchanged
• D. not rotate but its temperature will slowly rise

Answer 1

Answer: (B)

$\otimes$ is decreasing, so clockwise current in the square loop is induced.
So force (along the arrow) is acting on the disc.
So movement of disc is along the direction of motion of magnet.