Write the equation of electric field due to a point charge. Also name the terms in it.

A point $\mathrm{P}$ is $40 \mathrm{m}$ away from $20 \mathrm{\mu C}$ point charge and $20 \mathrm{m}$ from $4\mathrm{\mu C}$ point charge. The electric potential at point $\mathrm{P}$ is____$\mathrm{V}$.

($\mathrm{K}=9\times {10}^9{\mathrm{Nm}}^2{\mathrm{C}}^{-2}$)

The electric field lines of a positive charge is as shown in figure:

Give the sign of potential difference ${\mathrm{V}}_{\mathrm{p}}-{\mathrm{V}}_{\mathrm{q}}$.

An electric charge $Q$ is uniformly distributed around a semicircle of radius $a$. Calculate the electric potential at the centre of this semicircle.

The electric potential at the centre of two concentric half rings of radii $R_1$ and $R_2$, having same linear charge density $\lambda$ is

.

An electric dipole is placed as shown in the figure.

The electric potential (in ${10}^2 \mathrm{V}$) at point $P$ due to the dipole is (${\epsilon }_0$=permittivity of free space and $\frac{1}{4\pi {\epsilon }_0}=K$)