Derive an expression for torque acting on a bar magnet placed in a uniform magnetic field.

Explanation

Magnetic field It is a space around a magnet in which its influence can be felt. Uniform magnetic field: When magnetic field in a region is same everywhere then magnetic field is said to be uniform.
Non-uniform magnetic field: When magnetic field in a region is different at different points, then magnetic field is said to be non-uniform. Uniform magnetic field is represented by equal spaced parallel lines while non-uniform magnetic field is represented by non-parallel lines.

Torque acting on a magnetic dipole when placed in a uniform magnetic field