In a uniform magnetic field of 0.049 T , a magnetic needle performs 20 complete oscillations in 5 seconds as shown. The moment of inertia of the needle is 9.8 10^ -6 ~kg ~m ^2. If the magnitude of magnetic moment of the needle is x 10^ -5 Am ^2, then the value of ' x ' is :
C. 1280 ^2
Time period of Oscillation, T=2 I M B aligned & 1 4 =2 9.8 10^ -6 M 0.049 \\ & 1 16 =4 ^2 9.8 10^ -6 M 49 10^ -3 \\ & M= 4 ^2 9.8 10^ -6 49 10^ -3 16 \\ & = 4 ^2 9.8 16 10^ -3 49 \\ & =12.8 ^2 10^ -3 10^ -2 10^2 \\ & =1280 ^2 10^ -5 Am ^2 \\ & aligned
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