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

An electron is moving around the nucleus of a hydrogen atom in a circular orbit of radius $r$. The Coulomb force $\vec{F}$ between the two is

Two point charges of equal magnitude but opposite sign are placed at a certain distance. The force between them is $F$. If $75\%$ of the charge from one is transferred to the other,what will be the new force between them?

In a hydrogen-like system,the ratio of the Coulomb force to the gravitational force between an electron and a proton is of the order of:

$A$ 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 balls with equal charges are in a vessel with ice at $-10^{\circ} C$ at a distance of $25 \ cm$ from each other. On forming water at $0^{\circ} C$,the balls are brought nearer to $5 \ cm$ for the interaction between them to be same. If the dielectric constant of water at $0^{\circ} C$ is $80$,the dielectric constant of ice at $-10^{\circ} C$ is: