Two point charges $+8q$ and $ – 2q$ are located at $x = 0$ and $x = L$ respectively. The location of a point on the $x$-axis at which the net electric field due to these two point charges is zero is

The ratio of coulomb's electrostatic force to the gravitational force between an electron and a proton separated by some distance is $2.4 \times 10^{39}$. The ratio of the proportionality constant, $K=\frac{1}{4 \pi \varepsilon_0}$ to the Gravitational constant $G$ is nearly (Given that the charge of the proton and electron each $=1.6 \times 10^{-19}\; C$, the mass of the electron $=9.11 \times 10^{-31}\; kg$, the mass of the proton $=1.67 \times 10^{-27}\,kg$ ):

Two positive charges of $20$ $coulomb$ and $Q\;coulomb$ are situated at a distance of $60\,cm$. The neutral point between them is at a distance of $20\,cm$ from the $20\,coulomb$ charge. Charge $Q$ is…..$C$

By using Coulomb’s law, define unit charge.

Why Coulomb’s law is associated with Newton’s $3^{rd}$ law ?