A bar magnet is released from rest along the axis of a very long, ver…

The correct answer is Option (4) → move with almost constant speed

As the magnet falls, the magnetic flux through each ring of the copper tube changes, so eddy currents are induced in the tube. By Lenz's law these currents oppose the cause producing them, the motion of the magnet, so they exert an upward drag on it. The drag grows with the speed of the magnet. The magnet speeds up until the drag equals its weight; the net force is then zero, and it falls with an almost constant terminal speed.

Option (1) stop in the tube — Incorrect. The drag exists only while the magnet moves, so it can never stop the magnet; it only limits the speed.

Option (2) move with an acceleration equal to acceleration due to gravity — Incorrect. The upward drag makes the acceleration less than \( g \), and the acceleration falls to almost zero.

Option (3) oscillate — Incorrect. The drag always opposes the motion and never pushes the magnet upward, so there is no oscillation.

Option (4) move with almost constant speed — Correct. Once the drag balances the weight, the magnet moves with almost constant speed.

Note: A similar question was also asked in CUET (UG) 2026 on 29-05-2026 (Slot 1).

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Eddy Currents – “… You will see that the magnet takes much longer time in the case of aluminium pipe. Why is it so? It is due to the eddy currents that are generated in the aluminium pipe which oppose the change in magnetic flux, i.e., the motion of the magnet. The retarding force due to the eddy currents inhibits the motion of the magnet. Such phenomena are referred to as electromagnetic damping.”