In Milikan's oil drop experiment, an oil drop of radius `r` and charge `q` is held in equilibrium between the plates of as charged parallell plate capacitor when the potential difference is `V`. To keep as drop of radius `2`r and with a charge `2q` in equilibrium between the plates the potential difference `V` required is

Options

A. V
B. 2V
C. 4V
D. 8V

Answer

C

Explanation

`q((V)/(d))=mg=4/3pir^(3)rhog" "...(i)`
`2q(V')/(d)=4/3pi(2r)^(3)rhog`
or `(qV')/(d)=4/3pir^(3)rhogxx4`
`(qV')/(d)=4(qV)/(d)`
`thereforeV'=4V`