Question

A circular coil of N turns and diameter d carries a current I. It is unwound and rewound to make another coil of diameter 2d, current I remaining the same. Calculate the ratio of the magnetic moments of the new coil and original coil. ​

Answer 1

Explanation:

correct answer =2: 1

since the total length of the wire used remains the same,

N×πd=N' ×π(2d)

=N' =N\2

hence the ratio of the magnetic moment=M'/M

=1N'A'/1NA

=N'A'/NA

=N'd'2/Nd2

=2

hope it will help you.