question_answer

A copper ring is held horizontally and a bar magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet while it is passing through the ring is                  [CBSE PMT 1996; MP PET 1990, 99;                    CPMT 1991, 99; JIPMER 1997; CPMT 2003;                    MP PET/PMT 2001; KCET 2001; Kerala (Engg.) 2001]

A)            Equal to that due to gravity

B)            Less than that due to gravity

C)            More than that due to gravity

D)            Depends on the diameter of the ring and the length of the magnet

Correct Answer: B

Solution :

                   When the magnet is allowed to fall vertically along the axis of loop with its north pole towards the ring. The upper face of the ring will become north pole in an attempt to oppose the approaching north pole of the magnet. Therefore the acceleration in the magnet is less than g.                    Note : If coil is broken at any point then induced emf will be generated in it but no induced current will flow. In this condition the coil will not oppose the motion of magnet and the magnet will fall freely with acceleration g. (i.e. a = g)