In Millikan's oil drop experiment, a charged oil drop of mass `3.2xx10^(-14)kg` is held stationary between two parallel plates 6mm apart by applying a potential difference of `1200 V` between them. How many excess electrons does the oil drop carry? Take `g =10ms^(-2)`

Options

A. 7
B. 8
C. 9
D. 10

Answer

D

Explanation

According to figure. It is clear that electrical force is balanced by weight of body i.e.,
`qE=mg`
or `"ne"(V)/(r)=mg" "(becauseq="ne")`
`therefore nxx1.6xx10^(-19)xx(1200)/(6xx10^(-3))`
`=3.2xx10^(-14)xx10`
or `n=(3.2xx10^(-13)xx6xx10^(-3))/(1.6xx10^(-19)xx1200)`
`therefore n=10`