Question

A bar magnet of moment of inertia $4.9\times {10}^{-2}$ kgm${}^2$ vibrates in a magnetic field of induction $0.5\times {10}^{-4}T$. The time period of vibration is 8.8 sec. The magnetic moment of the bar magnet is :

• A. 350 Am${}^2$
• B. 490 Am${}^2$
• C. 3300 Am${}^2$
• D. 500 Am${}^2$

Answer 1

The correct option is D 500 Am${}^2$

The time period of oscillation is given by
$T=2\pi \sqrt{\frac{I}{MB}}$
$M=\frac{4{\pi }^{2}I}{B{T}^2}$

$M=500A{m}^2$