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Question: Answered & Verified by Expert
A charged oil drop falls with terminal velocity v0 in the absence of electric field. An electric field E keeps it stationary. The drop acquires charge 3q, it starts moving upwards with velocity v0. The initial charge on the drop is
PhysicsElectrostaticsNEET
Options:
  • A q2
  • B q
  • C 32q
  • D 2q
Solution:
1903 Upvotes Verified Answer
The correct answer is: 32q
When drop is stationary, then

q1E=6π ηr v0 or q1=6π ηr v0/E

When drop moves upwards, then

3q=6π ηrv0+v0E=2×6π ηrv0E=2q1

  q1=32q

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