One bar magnet is suspended so as to rotate freely in horizontal magnetic field. Then .....

Options

A. It would become steady along east-west direction.
B. It would become steady along north-south direction.
C. It would become steady along vertical direction.
D. None of these.

Answer

B

Explanation

At every place on the surface of Earth, magnetic field is in the magnetic meridian along north-south direction. Hence if a bar magnet is suspended so as to rotate freely in horizontal plane, it gets aligned along `overset(to)(B_h)` and so torque exerted on it becomes zero.
`tau= m(B_h) sin0^(@) = 0`
Thus, bar magnet attains stable equilibrium when its axis is along north-south direction, with `overset(to)(m)` pointing towards north.