Question

A bar magnet is released from rest along the axis of a very long, vertical aluminum tube. After sometime the magnet

• A. will stop in the tube.
• B. will move with an acceleration ${}^{\prime }{g}^{\prime }$.
• C. will move with almost constant speed.
• D. will oscillate.

Answer 1

Answer: (C)

will move with almost constant speed.

By Lenz's Law , as long as the magnet has a non zero acceleration, the flux linking with the aluminium tube will keep changing, and hence to opposes it a current and accompanying magnetic field will be induced that opposes that change in flux. This induced field will repel the the magnet in the direction opposite to its motion. Eventually the magnetic repulsion due to induced field by Lenz's Law will be equal to the gravitational pull on the magnet and it will reach a constant velocity.