An uniformly charged thin spherical shell of radius 'R' has uniform surface charge density '$\sigma$'. It is made of two hemispherical identical shells held together by pressing them with force 'F' as shown. F is proportional to
[$\epsilon_0$ = permittivity of free space]

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