When two spheres having $4 Q$ and $-2 Q$ charge are placed at a certain distance,the force acting between them is $F$. Now they are connected by a conducting wire and again separated from each other. Now they are kept at a distance half of the previous one. The force acting between them is . . . . . . .

The dimension of $\frac{1}{2} \varepsilon_0 E^2$ (where $\varepsilon_0$ is the permittivity of free space and $E$ is the electric field) is:

Which of the following processes involves the principle of electrostatic induction?

$F_g$ and $F_e$ represent the gravitational and electrostatic forces,respectively,between two electrons situated at a distance of $10 \ cm$. The ratio of $F_g/F_e$ is of the order of:

The Van de Graaff generator is not based on

Two identical charged spheres suspended from a common point by two massless strings of lengths $l$ are initially at a distance $d$ $(d << l)$ apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result,the spheres approach each other with a velocity $v$. Then $v$ varies as a function of the distance $x$ between the spheres,as: