A magnetic needle has magnetic moment of `6*7xx10^-2Am^2` and moment of inertial of `7*5xx10^-6kgm^2`. It perform `10` complete oscillations in `6*70s`. What is the magnitude of the magnetic field?

Explanation

The time period of oscillation is,
`T=(6.70)/(10)=0.67s`
From Eq. (5.5)
`B=(4pi^(2)g)/(m T)`
`=(4 xx (3.14)^(2) xx 7.5 xx 10^(-6))/(6.7 xx 10^(-2) xx (0.67)^(2))`
=0.01T