As shown in the figure, charges $+q, +q, -q$ and $-q$ are placed on the vertices of a square, each side length is $2l$. The electric potential at the mid-point '$A$' of the charges $+q$ and $+q$ is . . . . . . .

Three concentric spherical metallic shells $X$,$Y$,and $Z$ of radii $a$,$b$,and $c$ respectively $[a < b < c]$ have surface charge densities $\sigma$,$-\sigma$,and $\sigma$,respectively. The shells $X$ and $Z$ are at the same potential. If the radii of $X$ and $Y$ are $2\,cm$ and $3\,cm$,respectively,then the radius of shell $Z$ is $......\,cm$.

If the electric potential at a distance of $5 \, cm$ from the center of a charged conducting sphere of radius $10 \, cm$ is $V$,then what will be the potential at a point at a distance of $15 \, cm$ from the center?

Two unlike charges of magnitude $q$ are separated by a distance $2d$. The potential at a point midway between them is

The work done to take an electron from rest where potential is $-60\, V$ to another point where potential is $-20\, V$ is given by.....$eV$.

If on the concentric hollow spheres of radii $r$ and $R$ $(R > r)$ the charge $Q$ is distributed such that their surface charge densities are the same,then the potential at their common centre is: