Place a compass at a point on a curved magnetic field line. How do needle of the compass come to rest?

What causes for the couple acting on the needle of compass?

Copy the figure given below which shows a plotting compass and a magnet. Label the N pole of the magnet and draw the field line on which the compass lies.

Explain the method of plotting magnetic field lines by using a small compass needle.

Two short bar magnets have equal pole stengths but one is twice as long as the other one . The short magnet is placed at a distance of 30 cm in tan A position form the compass needle . The longer magnet must be placed on the other side of the compass needle for no deflection at a distance of .