What is the force between two small charged spheres having charges of $2 \times 10^{-7} C$ and $3 \times 10^{-7} C$ placed $30 cm$ apart in air?

$A$ charge $Q$ is placed at the midpoint of the line joining two identical point charges $q$. For what value of $q$ will the system be in equilibrium?

Two similar spheres having $+q$ and $-q$ charge are kept at a certain distance $r$. $A$ force $F$ acts between them. If another similar sphere having $+q$ charge is kept in the middle of the two spheres, then it experiences a force in magnitude and direction as:

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

Two particles with charges $+3.72 \mu C$ and $+1.86 \mu C$ are at some distance apart. If $20 \%$ of the charge is transferred from the first particle to the second particle,then the electrostatic force between them is

Two balls of same mass and carrying equal charge are hung from a fixed support of length $l$. At electrostatic equilibrium,assuming that the angle made by each thread is small,the separation $x$ between the balls is proportional to