If the potential of the inner shell of radius $r$ is $10\,V$ and that of the outer shell of radius $2r$ is $5\,V$, then the potential at the centre will be....$V$

If $27$ charged water droplets, each of radius $10^{-3} \,m$ and charge $10^{-12} \,C$ coalesce to form a single big spherical drop, then the potential of the big drop is (in $\,V$)

Six charges $+q, -q, +q, -q, +q$ and $-q$ are fixed at the corners of a hexagon of side $d$ as shown in the figure. The work done in bringing a charge $q_0$ to the centre of the hexagon from infinity is: ($\varepsilon_0$ = permittivity of free space)

$A$ solid conducting sphere, having a charge $Q$, is surrounded by an uncharged conducting hollow spherical shell. Let the potential difference between the surface of the solid sphere and that of the outer surface of the hollow shell be $V$. If the shell is now given a charge of $-4\, Q$, the new potential difference between the same two surfaces is......$V$.

$A$ and $C$ are concentric conducting spherical shells of radius $a$ and $c$ respectively. $A$ is surrounded by a concentric dielectric of inner radius $a$,outer radius $b$ and dielectric constant $k$. If sphere $A$ is given a charge $Q$,the potential at the outer surface of the dielectric (at radius $b$) is:

What is the electric potential at the center $O$ of a circle of radius $0.4 \ m$ with the charges arranged as shown in the figure?