$A$ point charge $A$ of $+10 \mu C$ and another point charge $B$ of $+20 \mu C$ are kept $1 \ m$ apart in free space. The electrostatic force on $A$ due to $B$ is $F_1$ and the electrostatic force on $B$ due to $A$ is $F_2$. Then:

The charges on two spheres are $+7\,\mu C$ and $-5\,\mu C$ respectively. They experience a force $F$. If each of them is given an additional charge of $-2\,\mu C$,the new force of attraction will be

Write the value of the Coulombian constant $k$ in $SI$ units.

If two particles $A$ and $B$ of charges $1.6 \times 10^{-19} \ C$ and $3.2 \times 10^{-19} \ C$ respectively are separated by a distance of $3 \ cm$ in air,then the magnitude of electrostatic force on particle $A$ due to particle $B$ is

$A$ point charge $q_1 = 4 q_0$ is placed at the origin. Another point charge $q_2 = -q_0$ is placed at $x = 12 \, cm$. The charge of a proton is $q_0$. $A$ proton is placed on the $x$-axis such that the net electrostatic force on it is zero. In this situation,the position of the proton from the origin is $.......... \, cm$.

Two spheres of radii $3 \ cm$ and $1 \ cm$ are placed at a distance of $10 \ cm$ from each other in a vacuum. If each sphere is charged to a potential of $10 \ V$,the force of repulsion between them is: