A coil carrying current l has radius r and number of turns n it is rewound so that radis of new coil is `(r )/(4)` and it carries current l the ratio fo magenic moment of new coil to that of original coil is

Options

A. 1
B. `(1)/(2)`
C. `(1)/(4)`
D. `(1)/(8)`

Answer

C

Explanation

`M=nIA=nIpir^(2) therefore Moo n r^(2)`
`(M_(2))/(M_(1))=(n_(2))/(n_(1))((r_(2))/(r_(1)))^(2)=(4n_(1))/(n_(1))((r)/(4r))^(2)=(1)/(4)`