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=2pisqrt(I/(MB_(H)))implies T prop 1/sqrt(M)impliesT_(1)/T_(2)=sqrt(M_(2)/M_(1))`,
If `M_(1)=100` then `M_(2)=(100-36)=64`
So `T_(1)/T_(2)=sqrt(64/100)=8/4impliesT_(2)=10/8T_(1)=1.25 T_(1)`
So % increase in time period `=25%`