A 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 remaining the same. Calculate the ratio of magnetic moments of the new coil and the original coil.

Explanation

`(M_("new"))/(M_("original"))= (21xxpi((r )/(2))^2)/(1xxpiR^2) = (1)/(2)` (As `N_2 =2N_1)`