Plot a graph showing the variation of coulomb force $\left(F\right)$ versus $\left(\frac{1}{r^2}\right)$ where $r$ is the distance between the two charges of each pair of charges: $(1\mu C, 2\mu C)$ and $(2\mu C, -3\mu C)$ Interpret the graphs obtained.

Four point charges are placed at the four corners of a square in the two ways (i) and (ii) as shown in Fig.  Will the electric field at the centre of the square, be the same or different in the two configurations and why?

Four point charges are placed at the four corners of a square in the two ways (i) and (ii) as shown in Fig. Will the electric potential, at the centre of the square, be the same or different in the two configurations and why?

Three charges$+q , +q$and $-2q$ are placed at the vertices of an equilateral triangle. What is the dipole moment of the system?

Two similar balls each having mass $m$ and charge $q$ are hung from a silk thread of length $l$. Prove that equilibrium separation,

$x={\left(\frac{q^{2}l}{2\pi {\epsilon }_{0}mg}\right)}^{1/3}$

when each thread makes a small angle $\theta$ with the vertical.