question_answer

Bob of a simple pendulum of length \[l\] is mode of iron. The pendulum is oscillating over a horizontal coil carrying direct current. If the time period of the pendulum is T then: [JEE ONLINE 23-04-2013]

A)        \[T=2\pi \sqrt{\frac{l}{g}}\] and damping is smaller than in air alone.

B)       \[T=2\pi \sqrt{\frac{l}{g}}\] and damping is larger than in air alone.

C)       \[T>2\pi \sqrt{\frac{l}{g}}\] and damping is smaller than in air alone.

D)       \[T<2\pi \sqrt{\frac{l}{g}}\] and damping is larger than in air alone.

Correct Answer: D

Solution :

[d] 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 and damping is larger than in air alone due energy dissipation.