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

1. 6.65 s
2. 8.89 s
3. 6.98 s
4. 8.76 s

Correct answer: 6.65 s

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