Six charges are placed at the corner of a regular hexagon as shown. If an electron is placed at its centre $O$, force on it will be:

Three point charges $q,-2 q$ and $2 q$ are placed on $x$-axis at a distance $x=0, x=\frac{3}{4} R$ and $x=R$ respectively from origin as shown. If $q =2 \times 10^{-6}\,C$ and $R =2\,cm$, the magnitude of net force experienced by the charge $-2 q$ is .......... $N$

In hydrogen like system the ratio of coulombian force and gravitational force between an electron and a proton is in the order of:

Write expression of Coulombian force acting between two charges kept in medium.

Three charges $+Q, q, +Q$ are placed respectively, at distance, $0, \frac d2$ and $d$ from the origin, on the $x-$ axis. If the net force experienced by $+Q$, placed at $x = 0$, is zero, then value of $q$ is

A point charge $q_1$ exerts an electric force on a second point charge $q_2$. If third charge $q_3$ is brought near, the electric force of $q_1$ exerted on $q_2$