Oscillations

JEE Main level, single correct, medium

192 of 194

Question 192 of 194

Bob of a simple pendulum of length ll is made of iron. The pendulum is oscillating over a horizontal coil carrying direct current. If the time period of the pendulum is T\mathrm{T} then :

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Answer: (D) T<2πlgT \lt 2 \pi \sqrt{\frac{l}{g}} and damping is larger than in air alone.

When the pendulum is oscillating over a current carrying coil, and when the direction of oscillating pendulum bob is opposite to the direction of current. Its instantaneous acceleration increases.
Hence time period T<2πℓg\mathrm{T} \lt 2 \pi \sqrt{\frac{\ell}{\mathrm{g}}} and damping is larger than in air alone due energy dissipation.

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