A charge $q$ is placed at the centre of the line joining two equal charges $Q$. The system of the three charges will be in equilibrium, if $q$ is equal to

Two positively charged spheres of masses $m_1$ and $m_2$ are suspended from a common point at the ceiling by identical insulating massless strings of length $l$. Charges on the two spheres are $q_1$ and $q_2$, respectively. At equilibrium, both strings make the same angle $\theta$ with the vertical. Then

Two charges, each equal to $q$, are kept at $x = -a$ and $x = a$ on the $x-$axis. A particle of mass $m$ and charge $q_0=\frac{q}{2}$ is placed at the origin. If charge $q_0$ is given a small displacement $(y < < a)$ along the $y-$axis, the net force acting on the particle is proportional to

An infinite number of charges, each of charge $1 \,\mu C$ are placed on the $x$-axis with co-ordinates $x = 1, 2,4, 8, ….\infty$. If a charge of $1\, C$ is kept at the origin, then what is the net force acting on $1\, C$ charge….$N$

How did Coulomb find the law of value of electric force between two point charges ?