Question

Two large vertical and parallel metal plates having a separation of 1cm are connected to a DC voltage source of potential difference X. A proton is released at rest midway between the two plates. It is found to move at `45^@` to the vertical JUST after release. Then X is nearly
A. (a) `1xx10^-5V`
B. (b) `1xx10^-7V`
C. (c) `1xx10^-9V`
D. (d) `1xx10^-10V`

Answer 1

Correct Answer - C
The two forces acting on the proton just after the release are shown in the figure. In this istuation `qE=mg` `[:. theta=45^@]`
`:.` `q(V/d)=mg`
`:.` `V=(mgd)/(q)=(1.67xx10^-27xx10xx10^-2)/(1.6xx10^-19)=10^-9V`