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Question: Answered & Verified by Expert
A simple pendulum of length L is placed between the plates of a parallel plate capacitor having electric field  E , as shown in figure. Its bob has mass m and charge  q . The time period of the pendulum is given by:
PhysicsElectrostaticsJEE MainJEE Main 2019 (10 Apr Shift 2)
Options:
  • A 2πLg2+qEm2
  • B 2πLg+qEm 
  • C 2πLg-qEm 
  • D 2πLg2-q2E2m2
Solution:
2627 Upvotes Verified Answer
The correct answer is: 2πLg2+qEm2


Two forces will be acting on the mass m, gravity force and force by the electric field.

Thus, the effective force =  qE2+mg2
From force equation, geff=g2+qEm2
Time period of the pendulum is T=2πLgeff
=2π Lg2+qEm2

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