A magnetic needle has a magnetic moment `5.0xx10^(-2)" Am^(2)` and moment of inertia of `7.8xx10^(-6)"kg m"^(2)`, it performs 12 complete oscillations in 6.0 s. What is the magnitude of magnetic field ?

Options

A. 0.0016 T
B. 0.16 T
C. 1.6 T
D. 16 T

Answer

A

Explanation

Here, `m=5.0xx10^(-2)` A `m^(2)`
T = 0.65 s, I = `8.5xx10^(-7)` Kg `m^(2)`
`B=(4pi^(2)I)/(mT^(2))=(4xx(3.14)^(2)xx8.5xx10^(-7))/(5xx10^(-2)xx(0.65)^(2))`
`" "=158.69xx10^(-5)` T = 0.0016 T