A magnetised wire of magnetic moment M and length I is bent in the form of a semi-cycle of radius r. The new magnetic moment is

Magnetic moment M = mlWhen the magnet is bent in the form of a semicircle of radius r, the distance between poles becomes 2 r. The new magnetic moment isM′=m(2r)∴M′M=m(2r)ml=2rlBut l=πr∴M′M=2π.