In a hydrogen atom,the distance between the electron and proton is $2.5 \times 10^{-11} \ m$. The electrical force of attraction between them will be

In a right-angled triangle $ABC$,$AB = 3 \ cm$,$BC = 4 \ cm$,and $\angle ABC = \frac{\pi}{2}$. Charges of $+15 \ e.s.u.$,$+12 \ e.s.u.$,and $-20 \ e.s.u.$ are placed at $A$,$B$,and $C$ respectively. What is the net force on the charge at $B$ in $dynes$?

Two equally charged metal spheres $A$ and $B$ repel each other with a force of $4 \times 10^{-5} \ N$. Another identical uncharged sphere $C$ is touched to $A$ and then placed at the midpoint of the line joining the spheres $A$ and $B$. The net electric force on the sphere $C$ is

Two balls with charges $+7 \ \mu C$ and $-5 \ \mu C$ attract each other with a force $F$. If $-2 \ \mu C$ charge is added to both,what will be the force between them?

For the regular pentagon system shown in the figure,find the net electrostatic force on the charge $q_0$ placed at the center.

Two small spheres each having the charge $+Q$ are suspended by insulating threads of length $L$ from a hook. This arrangement is taken into space where there is no gravitational effect. Then the angle between the two suspensions and the tension in each will be: