The number of electrons to be put on a spherical conductor of radius `0.1m` to produce an electric field of `0.036N//C` just above its surface is

Options

A. `3.4xx10^5`
B. `2.5xx10^5`
C. `3.7xx10^5`
D. `4.7xx10^5`

Answer

B

Explanation

`E=1/(4piepsilon_0)Q/R^2`
`rArr 0.036=9xx10^9Q/(0.1)^2`
`rArr Q=(0.036xx(0.1)^2)/(9xx10^9)=4xx10^(-14)` C
Let the number of electrons needed to create this much amount of charge be n
`rArr n=Q/e =(4xx10^(-14))/(1.6xx10^(-19))=2.5xx10^5`