A magnetic needle of magnetic moment 6.7 × 10⁻² Am² and moment of inertia 7.5 × 10⁻⁶ kg m² is performing simple harmonic oscillations in a magnetic field of 0.01 T. Time taken for 10 complete oscillations is :
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Question

A magnetic needle of magnetic moment 6.7 × 10⁻² Am² and moment of inertia 7.5 × 10⁻⁶ kg m² is performing simple harmonic oscillations in a magnetic field of 0.01 T. Time taken for 10 complete oscillations is :

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G1 Physics · Accepted Answer

For small oscillations of a magnetic needle, T=2π√(I/(MB)). With I=7.5×10⁻⁶ kg·m², M=6.7×10⁻² A·m² and B=0.01 T, one period is about 0.665 s; 10 oscillations take 6.65 s. Hence C.