In Fig, the magnetic needle has magnetic moment `6.7 xx 10^(-2) Am^(2)` and moment of intertia `I = 7.5 xx 10^(-6) kg m^(2)`. It performs 10 complete oscillations is 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. `B = (4pi^(2)I)/(mT^(2))`
`= (4 xx (3.14)^(2) xx 7.5 xx 10^(-6))/(6.7 xx 10^(-2) xx (0.67)^(2))`
`= 0.01 T`