A magnet makes `40` oscillations per minute at a place having magnetic field intensity of `0.1xx10^(-5)T`. At another place, it takes 2.5 sec to complete one vibrating. The value of earth's horizontal field at that place is

Options

A. `0.25xx10^(-6)T`
B. `0.36xx10^(-6)T`
C. `0.66xx10^(-8)T`
D. `1.2xx10^(-6)T`

Answer

b

Explanation

(b) `T_(1)=(60)/(40)=1.5s and T_(2)=2.5s`
We know that, `(T_(1))/(T_(2))=sqrt((B_(2))/(B_(1))`
or `B_(2)=(T_(1)^(2))/(T_(2)^(2))xxB_(1)=((1.5)/(2.5))^(2)xx(0.1xx10^(-5))=0.36xx10^(-6)T`