Two charges,each of $1\;C$,are at a distance of $1\;km$ apart. The force between them is:

Two spheres carrying charges $+6 \mu C$ and $+9 \mu C$ are separated by a distance $d$ and experience a force of repulsion $F$. When a charge of $-3 \mu C$ is added to both spheres and they are kept at the same distance as before,the new force of repulsion is:

Three identical charged balls,each of charge $2 \, C$,are suspended from a common point $P$ by silk threads of $2 \, m$ each (as shown in the figure). They form an equilateral triangle of side $1 \, m$. The ratio of the net electrostatic force on one charged ball to the force between any two charged balls is ...........

$A$ charge $Q$ is to be divided between two objects. The values of the charges on the objects so that the electrostatic force between them will be maximum is

If two charges of $1 \,C$ each are placed $1 \,km$ apart,then the force between them will be ........... $N$.

Three charges $4q, Q$ and $q$ are placed at positions $0, \frac{l}{2}$ and $l$ respectively along a straight line. If the resultant force on $q$ is zero,then $Q$ is equal to