A circular coil of N turns and radius R carries a current I. It is unwound and rewound to make another coil of radius R/2, current I remaining the same. Calculate the ratio of the magnetic moments of the new coil and the original coil.
Length of the wire remains same,
Magnetic moment of a coil, m = NAI
For the coil of radius R, magnetic moment,
Magnetic moment for coil of radius R/2,
Therefore,