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A bar-magnet of moment of inertia $49 \times 10^{-2} \mathrm{~kg}-\mathrm{m}^2$ vibrates in a magnetic field of induction $0.5 \times 10^{-4} \mathrm{~T}$. The time period of vibration is $8.8 \mathrm{~s}$. The magnetic moment of the bar magnet is
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5000 A-m ${ }^2$
Time period of magnet is
$\begin{aligned} \quad T & =2 \pi \sqrt{\frac{I}{M H}} \\ \text { or } \quad M & =\frac{4 \pi^2 I}{T^2 H} \\ \text { or } \quad M & =\frac{4 \times(3.14)^2 \times 49 \times 10^{-2}}{(8.8)^2 \times 0.5 \times 10^{-4}} \\ \text { or } \quad M & =5000 \mathrm{~A}-\mathrm{mf}^2\end{aligned}$
$\begin{aligned} \quad T & =2 \pi \sqrt{\frac{I}{M H}} \\ \text { or } \quad M & =\frac{4 \pi^2 I}{T^2 H} \\ \text { or } \quad M & =\frac{4 \times(3.14)^2 \times 49 \times 10^{-2}}{(8.8)^2 \times 0.5 \times 10^{-4}} \\ \text { or } \quad M & =5000 \mathrm{~A}-\mathrm{mf}^2\end{aligned}$
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