A magnet is suspended in the magnetic meridian with an untwisted wire. The upper end of wire is rotated through `180^(@)` to deflect the magnet by `30^(@)` from magnetic meridian. When this magnet is replaced by another magnet, the upper end of wire is rotated through `270^(@)` to deflect the magnet `30^(@)` from magnetic meridian. The ratio of magnetic moment of magnets is

Options

A. `1:5`
B. `1:8`
C. `5:8`
D. `8:5`

Answer

C

Explanation

As `tau = MB sin theta and tau = k phi`
`therefore phi prop MB sin theta rArr phi prop M`
`rArr (phi_(1))/(phi_(2))= (M_(1))/(M_(2)) rArr (M_(1))/(M_(2)) = (150 xx (pi)/(180))/(240 xx (pi)/(180))`
`M_(1): M_(2)= 5: 8`