Question

When a current in a circular loop is equivalently replaced by a magnetic dipole,

Options

• the pole strength m of each pole is fixed

• the distance d between the poles is fixed

• the product md is fixed

• none of the above

Answer 1

 the product md is fixed

When we replace a circular current-carrying loop with a magnetic dipole to resemble field lines of the circular loop, the pole strength m and the distance between the poles are not fixed.
But the magnetic dipole moment of both systems is always fixed. It is the product of the magnetic moment and the distance between the poles. In other words, md is fixed.
A current loop of area A and current I can be replaced with a magnetic dipole of dipole moment md.
i.e. md = IA