The capacitance of a spherical capacitor is $100 \ pF$. If the spacing between the two spheres is $1 \ cm$,then the radius of the inner sphere of the capacitor is: (in $cm$)

The capacitance (in $F$) of a spherical conductor with a radius of $1\, m$ is:

Earth is assumed to be a charged conducting sphere having volume $V$ and surface area $A$. The capacitance of the earth in free space is ($\epsilon_0=$ permittivity of free space).

$A$ spherical capacitor consists of two concentric spherical conductors,held in position by suitable insulating supports. Show that the capacitance of a spherical capacitor is given by $C = \frac{4 \pi \varepsilon_{0} r_{1} r_{2}}{r_{1} - r_{2}}$,where $r_{1}$ and $r_{2}$ are the radii of outer and inner spheres,respectively.

The unit of electric permittivity is

$64$ small drops of water having same charge and same radius are combined to form one big drop. The ratio of capacitance of the big drop to the small drop is . . . . . . .