Question

the compass has unipolar magnet

Answer 1

The field of a bar magnet has a lot of divergence in it (the field rapidly gets weaker with distance) - and that is the prerequisite for attracting another bar magnet (like a compass needle). If you think of a bar magnet as a "North monopole" and a "South monopole", then one will be in a stronger field than the other - which is why there is a net attraction. Of course that's not really how magnets work, but I believe it helps your intuition.

In a purely uniform magnetic field, there is no attractive force on a bar magnet - only torque. But that is a situation that hardly ever arises.

Hope it helps you........!☺️☺️