The angle between an equipotential surface and the electric lines of force is .......$^o$.

The figure shows equipotential surfaces concentric at $O$. The magnitude of the electric field at a distance $r$ metres from $O$ is

Assertion $(A):$ $A$ spherical equipotential surface is not possible for a point charge.
Reason $(R):$ $A$ spherical equipotential surface is possible inside a spherical capacitor.

The figure shows three points $A, B$ and $C$ in a region of uniform electric field $E$. The line $A B$ is perpendicular and $B C$ is parallel to the field lines. Then,which of the following holds good? ($V_{A}, V_{B}$ and $V_{C}$ represent the electric potential at points $A, B$ and $C$,respectively)

Assertion $(A)$: In a region of constant potential,the electric field is zero and there can be no charge inside the region.
Reason $(R)$: According to Gauss's law,the charge inside the region should be zero if the electric field is zero.

Work done in moving a positive charge on an equipotential surface is