A point charge is placed at the centre of spherical Gaussian surface. How will electric flux ${\varphi }_E$ change if the sphere is replaced by a cube of same or different volume?

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.