A magnet is dropped down an infinitely long vertical copper tube 
 

Given data:

A magnet is moving down

Concepts used: Magnetic induction

Explanation:

The magnet moves with a steady increase in speed until it reaches a constant final speed of

When a magnet falls through an infinitely long copper tube, the magnetic flux changes continuously with the various cross-sections of the copper tube.

This change in magnetic flux associated with the copper tube induces a current in the copper tube.

According to Lenz's Law, the induced current exerts an upward force on the magnet as it opposes the changing magnetic field associated with the copper pipe.

Another force acting on the magnet is its downward self-weight.

Since the magnet is initially in free fall and is moving under the influence of gravity, the velocity of the magnet increases downwards or the net acceleration of the magnet is downwards.

Therefore, when a magnet falls vertically into a copper pipe, it moves with increasing speed until it reaches a constant speed.

The correct answer is A