Two point charges placed in air separated by distance $R$ exert a force $F$ on each other. Now the space between those charges is filled with a medium of dielectric constant $K$. At distance $R_1$ between the charges, the same force is exerted as $F$. Then:

If the distance between two point charges $+Q$ and $-Q$ is doubled,what will be the magnitude of the electrostatic force between them?

Two point charges $+q_{1}$ and $+q_{2}$ are placed a finite distance '$d$' apart. It is desired to put a third charge $q_{3}$ in between these two charges so that $q_{3}$ is in equilibrium. This is

Two electric charges are arranged as shown in the figure. Where should a third charge be placed so that it remains in equilibrium?

Three charges $q$,$Q$,and $4q$ are placed in a straight line of length $l$ at points distant $0$,$\frac{l}{2}$,and $l$ respectively from one end. In order to make the net force on $q$ zero,the charge $Q$ must be equal to

Two small balls,each having a negative charge $Q$,are suspended from a fixed point by two identical insulating strings of length $L$. This entire arrangement is placed inside a satellite in a region where there is no gravity (weightless condition). The angle between the strings is ......... and the tension in each string is ......... Newtons.