If a unit positive charge is shifted from a region of low potential to a region of high potential,then the electric potential energy of the system

Two concentric hollow spheres of radii $r$ and $R$ $(R > r)$ have the same surface charge density $\sigma$. The total charge $Q$ is distributed between them. The electric potential at the common center is:

Two conducting spheres of radii $r_1$ and $r_2$ are equally charged. The ratio of their potentials is (potential of $r_1$ to potential of $r_2$):

$A$ regular hexagon of side $10 \text{ cm}$ has a charge of $1 \mu\text{C}$ at each of its vertices. The potential at the centre of the hexagon is $\left[\frac{1}{4 \pi \varepsilon_0} = 9 \times 10^9 \text{ SI unit}\right]$.

Electron volt is a unit of

Two small equal point charges of magnitude $q$ are suspended from a common point on the ceiling by insulating massless strings of equal lengths. They come to equilibrium with each string making an angle $\theta$ from the vertical. If the mass of each charge is $m$,then the electrostatic potential at the centre of the line joining them will be $\left( \frac{1}{4\pi \epsilon_0} = k \right).$