Question

In Millikan oil drop experiment, a charged drop of mass `1.8 xx 10^(-14) kg` is stationary between its plates. The distance between its plates is `0.90 cm` and potential difference is `2.0` kilo volts. The number of electrons on the drop is
A. `500`
B. `50`
C. `5`
D. `0`

Answer 1

Correct Answer - C
`QE = mg rArr Q = (mg)/(E) rArr n = (mgd)/(Ve)`
`rArr n = (1.8 xx 10^(-14) xx 10 xx 0.9 xx 10^(-2))/(2 xx 10^(3) xx 1.6 xx 10^(-19)) = 5`