A magnetic needle has a magnetic moment of `5 xx 10^(-2) Am^(2)` and moment of inertia `8xx10^(-6)` kg `m^(2)`. It has a period of oscillation of 2 s in a magnetic field `vecB`. The magnitude of magnetic field is approximately

Options

A. `3.2 xx 10^(-4)` T
B. `1.6 xx 10^(-4)` T
C. `0.8 xx 10^(-4)` T
D. `0.4 xx 10^(-4)` T

Explanation

`(""^(***)): T = 2pisqrt(I/(MB))`
`T^(2) = (4pi^(2)I)/(MB) rArr B = (4pi^(2)I)/(T^(2)M)`
`= (4xx(3.14)^(2)xx8xx10^(-6))/(4xx5xx10^(-2)) = 15.77 xx 10^(-4) T ~~ 1.6xx10^(-3)T`
`""^(***)`None of the given options is correct.