Question

A bar magnet falls along the axis of a circular current carrying loop. The direction of current (i) is as indicated. What can be said about the acceleration of the bar magnet when it comes near the coil?

• A. a < g
• B. a = 0
• C. a = g
• D. a > g

Answer 1

The correct option is A

a < g

According to the Lenz's law, a reverse magnetic flux is induced in circuit when the external flux through a coil is varied with time. Hence when bar magnet falls through coil, the magnetic flux inside it increases with time in the downward direction. Hence an anticlockwise current is induced in coil to produce magnetic field in upward direction which will induce North pole.
Due to this the repulsive force, a retarding force acts on the magnet upwards and thus the acceleration is less than g.