The magnet of vibration magnetometer is heated so as to reduce its magnetic moment by 36%. By doing this the periodic time of the magnetometer will

Options

A. Increases by 36%
B. Increases by 25%
C. Decreases by 25%
D. Decreases by 64%

Answer

B

Explanation

`T= 2pi sqrt(I/(MB))`
`T prop sqrt(I/M) rArr T_(1)/T_(2) = sqrt(M_(2)/M_(1))`
If `M = 100%`, then `M_(2) = (100 - 36)% = 64%`
`T_(1)/T_(2) = sqrt(64%/100%) = 8/10`
`T_(2) = 10/8 T_(1) rArr T_(2) = 1.25 T_(1)`