Draw electric field by negative charge.

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 ............ $Nm ^2 C ^{-1}$

A square surface of side $L$ meter in the plane of the paper is placed in a uniform electric field $E(volt/m)$ acting along the same plane at an angle $\theta$ with the horizontal side of the square as shown in figure.The electric flux linked to the surface, in units of $volt \;m $

A charge $+q$ is placed somewhere inside the cavity of a thick conducting spherical shell of inner radius $R_1$ and outer radius $R_2$. A charge $+Q$ is placed at a distance $r > R_2$ from the centre of the shell. Then the electric field in the hollow cavity

It is not convenient to use a spherical Gaussian surface to find the electric field due to an electric dipole using Gauss’s theorem because

Assertion : Four point charges $q_1,$ $q_2$, $q_3$ and $q_4$ are as shown in figure. The flux over the shown Gaussian surface depends only on charges $q_1$ and $q_2$.

Reason : Electric field at all points on Gaussian surface depends only on charges $q_1$ and $q_2$ .