An infinite line charge is at the axis of a cylinder of length $1 \,m$ and radius $7 \,cm$. If electric field at any point on the curved surface of cylinder is $250 \,NC ^{-1}$, then net electric flux through the cylinder is ............ $Nm ^2 C ^{-1}$

When the electric flux associated with closed surface becomes positive, zero or negative ?

The black shapes in the figure below are closed surfaces. The electric field lines are in red. For which case, the net flux through the surfaces is non-zero?

Total electric flux coming out of a unit positive charge put in air is

A positive charge $q$ is kept at the center of a thick shell of inner radius $R_1$ and outer radius $R_2$ which is made up of conducting material. If $\phi_1$ is flux through closed gaussian surface $S_1$ whose radius is just less than $R_1$ and $\phi_2$ is flux through closed gaussian surface $S_2$ whose radius is just greater than $R_1$ then:-

Two charges of $5 Q$ and $-2 Q$ are situated at the points $(3 a, 0)$ and $(-5 a, 0)$ respectively. The electric flux through a sphere of radius $4a$ having center at origin is