In the given diagram,find the distance of the neutral point from the particle of charge $e$ in $cm$.

The unit of permittivity of free space ${\varepsilon _0}$ is

Two identical conducting spheres having unequal positive charges $q_1$ and $q_2$ are separated by a distance $r$. If they are made to touch each other and then separated again to the same distance $r$,the electrostatic force between the spheres in this case will be (neglect induction of charges):

Two identical balls having like charges $Q_1$ and $Q_2$ are placed at a distance $r$ apart and repel each other with a force $F$. They are brought in contact and then moved apart to a distance equal to half their initial separation. The force of repulsion between them increases $4.5$ times in comparison with the initial value. The ratio of the initial charges of the balls, $\frac{Q_1}{Q_2}$, is:

Identify the wrong statement in the following. Coulomb's law correctly describes the electric force that

Write the limitations of Coulomb's law.