$A$ metallic spherical shell has an inner radius $R_1$ and outer radius $R_2$. $A$ charge $Q$ is placed at the centre of the spherical cavity. What will be the surface charge density on the inner surface?

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 $4 a$ having its center at the origin is

$A$ charge is kept at the central point $P$ of a cylindrical region. The two edges subtend a half-angle $\theta$ at $P$, as shown in the figure. When $\theta=30^{\circ}$, then the electric flux through the curved surface of the cylinder is $\Phi$. If $\theta=60^{\circ}$, then the electric flux through the curved surface becomes $\Phi / \sqrt{n}$, where the value of $n$ is. . . . . . .

$A$ point charge '$q$' coulomb is placed at the centre of a cube of side length '$L$'. Then the electric flux linked with each face of the cube is

Draw the electric field lines for a positive point charge.

Consider the four surfaces $S_1, S_2, S_3,$ and $S_4$ enclosing the same charge $q_1$ as shown in the figure. Compare the electric flux through these surfaces.