Question

The total flux coming out of the cylinder of radius r and height h placed in a uniform electric field is

Answer 1

answer : zero

explanation : electric flux is the $\textbf{total}$ number of electric lines of force passing through in a given area. e.g., electric flux = electric field × cross sectional area.

by this concept you may answer , electric flux = E × πr²h = πr²hE , but this is not true.

actually, The number of electric lines of force entering the cylinder is same as that leaving it.

means, electric flux through first cross sectional surface, $\phi_1=\pi r^2hE$

and electric flux through 2nd cross sectional surface, $\phi_2=-\pi r^2hE$

so, net electric flux through the closed surface {e.g., cylinder} = πr²hE -πr²hE = 0

Therefore, the net electric flux through the cylinder is zero.

[ note : - The flux associated with any type of closed surface in a uniform electric field is zero.]