Question

Three identical bar magnets are rivetted together at centre in the same plane as shown in figure. This system is placed at rest in a slowly varying magnetic field. It is found that the system of magnets does not show any motion. The north-south poles of one magnet is shown in the figure. Determine the poles of the remaining two.

Answer 1

If the net force on the system is zero and net torque on the system is also zero, then the system will be in stable equilibrium. This is possible only when the poles of the remaining two magnets are as shown below.

The north pole of magnet (1) is equally attracted by south poles of (2) and (3) magnets placed at equal distance.

Similarly, one pole of any one magnet is attracted by opposite poles of other two magnets so resultant force or moment of each magnet is zero and will not be in motion placed on table.