Plot the graph of $E$ versus $\left(\frac{1}{r}\right)$ where $E$ is electric field due to a point charge and $r$ is the distance from the charge.

Three point charges $q\text{,} -2q \text{and} -2q$ are placed at the vertices of an equilateral triangle of side $a$. Find the work done by external forces to increase their separation to $2a$?

Two electrons lying $10 \mathrm{cm}$ apart are released. What will be their speed when they are $20 \mathrm{cm}$ apart?

Determine the electrostatic potential energy of a system consisting of two charges $7\mu C \text{and} -2\mu C$ (and with no external field) placed at $\left(-9 \mathrm{cm}\text{,} 0\text{,} 0\right) \text{and} \left(9 \mathrm{cm}\text{,} 0\text{,} 0\right)$, respectively.

There are two charges $7\mu \mathrm{C} \text{and} -2\mu \mathrm{C}$ (and with no external field) placed at $\left(-9 \mathrm{cm}\text{,} 0\text{,} 0\right)$ and $(9 \mathrm{cm}\text{,} 0\text{,} 0)$, respectively. How much work is required to separate them to an infinitely large distance?

A point $P$ is located $9 \mathrm{cm}$ away from a charge of $4\times {10}^{-7} \mathrm{C}$. Obtain the value of work done in bringing a charge of $2\times {10}^{-9} \mathrm{C}$ from infinity to the point $P$. Does the answer depend on the path along which the charge is brought?

What is the difference in potentials between two points, one at $10 \mathrm{cm}$ and the other at $20 \mathrm{cm}$ distance from a charge of $-5.5\mu \mathrm{C}$?