An electron falls from rest through a vertical distance h in a uniform and vertically upward directed electric field E. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical distance h. The time of fall of the electron, in comparison to the time of fall of the proton is

Options

A. 10 times greater
B. 5 times greater
C. smaller
D. Equal

Answer

C

Explanation

Given directions of electric fields , both the charged particles (electron and proton) will be experiencing electric force in the downward direction.
F=eE+mg
`a="eE"/(m+g)`
Charged particle is dropped from height h and coming down in time t
`h=1/2 "eE"/(m+g)t^2`
`l=sqrt(2h)/("eE"/(m+g))`
Everything is same for both the particles except mass. And we can see from the above result that electron will taken smaller time because its mass is less .