1) 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 A) 8.89 s B) 6.98 s C) 8.76 s D) 6.65 s Answer: Option DExplanation:Time period of oscillations is $T = 2\pi \sqrt{\frac{I}{MB}}$ $T = 2\pi \sqrt{\frac{7.5\times 10^{-6}}{6.7\times 10^{-2}\times 0.01}}$ =0.665 s Hence , time for 10 oscillations is t= 6.65 s
