The potential at a point,due to a positive charge of $100\,\mu C$ at a distance of $9\,m$,is

In the rectangle shown below,two corners have charges $q_1 = -5\,\mu C$ and $q_2 = +2.0\,\mu C$. The work done in moving a charge $q_0 = +3.0\,\mu C$ from $B$ to $A$ is ......... $J$. (Given: $1/4\pi\varepsilon_0 = 10^{10}\,N\cdot m^2/C^2$)

$A$ 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.

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

Energy of electrons can be increased by allowing them

There are two thin wire rings,each of radius $R$,whose axes coincide. The charges of the rings are $q$ and $-q$. The magnitude of potential difference between the centres of the rings separated by a distance $\sqrt{3} R$ is