Force between $A$ and $B$ is $F$. If $75\%$ charge of $A$ is transferred to $B$ then force between $A$ and $B$ is

If potential at centre of uniformaly charged ring is $V_0$ then electric field at its centre will be (assume radius $=R$ )

Four dipoles having charge $ \pm e$ are placed inside a sphere. The total flux of ${\vec E}$ coming out of the sphere is 

 An insulator plate is passed between the plates of a capacitor. The the displacement current

A solid coducting sphere having a charge $Q$ is surrounded by an uncharged concentric  conducting hollow spherical shell. Let the potential difference between the surface of the  solid sphere and that of the outer surface of the hollow shell be $V$. If the shell is now  given a charge $-3Q$, the new potential difference between the same two surface is :-........$V$

There is a square gaussian surface placed in $y-z$ plane. Its axis is along $x-$ axis and centre is at origin. Two identical charges, each $Q$, are placed at point $(a, 0, 0)$ and $(-a, 0, 0)$. Each side length of square is $2a$ then electric flux passing through the square is