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An ail drop having charge 2e is kept sta...

An ail drop having charge `2e` is kept stationary between two parallel horizontal plates `2.0 cm` apart when a potential difference of `12000` volts is applied between them. If the density of oil is `900 kg//m^(3)`, the radius of the drop will be

A

`2.0 xx10 ^(-6) m`

B

`1.7 xx10^(-6)m`

C

`1.4 xx10^(-6)m`

D

`1.1 xx10^(-6)m`

Text Solution

Verified by Experts

The correct Answer is:
B
In equilibrium `impliesqE = mg = (4/3pir^2rho)g`
`impliesq (V/d)=(4/3pir^3rho)g`
`implies 2xx1.6 xx10^(-19) xx(12000)/(0.02) =4/3 pir^3 xx900 xx10`
`implies r^3 =(2xx1.6 xx10^(-19)xx3 xx12)/(9xx2 xx10^(-2)xx4 xxpi)=16/pi xx10^(-18)`
`implies r = 1.72 xx10^(-6) m ~~ 1.7 xx10^(-6)m`
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