Four point charges each $+q$ are placed on the circumference of a circle of diameter $2d$ in such a way that they form a square. The potential at the centre is proportional to

Derive an expression for the electric potential at a point due to a system of $N$ charges.

If a $10 \mu C$ charge exists at the centre of a square,the work done in moving a $2 \mu C$ point charge from corner $A$ to corner $B$ of a square $ABCD$ is

What is the electric potential at a distance of $9 \text{ cm}$ from a charge of $3 \text{ nC}$ (in $\text{ V}$)?

$A$ charge $(-q)$ and another charge $(+Q)$ are kept at two points $A$ and $B$ respectively. Keeping the charge $(+Q)$ fixed at $B$,the charge $(-q)$ at $A$ is moved to another point $C$ such that $ABC$ forms an equilateral triangle of side $l$. The net work done in moving the charge $(-q)$ is

In the following diagram,the work done in moving a point charge from point $P$ to points $A$,$B$,and $C$ is $W_A$,$W_B$,and $W_C$ respectively. Then: