Two equal positive charges each of value 'q' are placed at points A and B, where $AB = 3x$. A third charge $-3q$ is placed at point C at a distance $x$ from A on AB. The potential energy of the system is nearly ($\epsilon_0$ = permittivity of free space)

A particle of mass 'm' and charge 'q', initially at rest, is accelerated by a uniform electric field 'E' through a distance 'D' and is then allowed to approach a fixed static charge 'Q' of the same sign. The distance of the closest approach of the charge q is
[ $\epsilon_0$ = permittivity of free space ]

'$n$' small spherical drops of the same size which are charged to 'V' volt each coalesce to form a single big drop. The potential of a big drop is

Two electric dipoles of moment $P$ and $8P$ are placed in opposite directions on a line at a distance of $24$ cm. The electric field will be zero at the point between the dipoles whose distance from the dipole of moment $P$ will be $x_1$. When $8P$ is replaced by $27P$ keeping all other quantities the same, the distance $x_1$ now becomes $x_2$. The difference $|x_2 - x_1|$ is ( All the distances are measured from the centers of the dipole.)