1.

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 beA. `2.0 xx 10^(-6) m`B. `1.7 xx 10^(-6) m`C. `1.4xx 10^(-6) m`D. `1.1 xx 10^(-6) m`

Answer» Correct Answer - B
In equilibrium `QE = mg`
`rArrQ. (V)/(d) = mg = ((4)/(3)pi r^(3) rho) g`
`rArr 2 xx 1.6 xx 10^(-19) xx (12000)/(2 xx 10^(-2)) = (4)/(3)pi r^(3) xx 900 xx 10`
`rArr r = 1.7 xx 10^(-6)m`


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