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

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

A dipole having dipole moment $p$ is placed in front of a solid uncharged conducting  sphere are shown in the diagram. The net potential at point $A$ lying on the surface of the sphere is :-

The figure shows two parallel equipotential surfaces $A$ and $B$ kept a small distance $r$ apart from each other. $A$ point charge of $q$ coulomb is taken from the surface $A$ to $B$. The amount of net work done will be

A capacitor $C = 100$ $ \mu F$ is connected to three resistors each of resistance $1$ $kW$ and a battery of emf $9$ $V$. The switch $S $ has been closed for long time so as to charge the capacitor. When switch $S $ is opened, the capacitor discharges with time constant.....$ms$ 

A point charge $q$ is placed at a distance $\frac{a}{2}$ directly above the centre of a  square of side $a$ . The electric flux through the square is