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An oil drop carrying a charge q has a ma...

An oil drop carrying a charge q has a mass m kg. If is falling freely in air with terminal speed v. The electric field required to make the drop move upwards with the same speed is

A

`(mg)/q `

B

`(2mg)/q `

C

`(mgv)/q^2`

D

`(2mgv)/q`

Text Solution

Verified by Experts

The correct Answer is:
B
To move the oil drop upward with terminal velocity v
`qE =mg+6pi eta rv`
As `mg=6pi eta rv`
`:. E = (2mg)/q`
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