Two identical positive charges are placed at $x = -a$ and $x = a$. The correct variation of potential $V$ along the $x$-axis is given by:

$A$ small sphere of radius $r_{1}$ and charge $q_{1}$ is enclosed by a spherical shell of radius $r_{2}$ and charge $q_{2}$. Show that if $q_{1}$ is positive,charge will necessarily flow from the sphere to the shell (when the two are connected by a wire) no matter what the charge $q_{2}$ on the shell is.

The electric potential inside a conducting sphere:

$A$ solid conducting sphere with charge $Q$ is surrounded by an uncharged concentric conducting spherical shell. Let $V$ be the potential difference between the surface of the solid sphere and the outer surface of the shell. If the shell is now given a charge of $-3Q$,the new potential difference between the two surfaces is .........$V$.

Find the electric potential at the origin due to the given distribution of charges.

Four electric charges $+q, +q, -q$, and $-q$ are placed in order at the corners of a square of side $2r$. The electric potential at a point midway between the two negative charges is