The respective radii of the two spheres of a spherical condenser are $12 \; cm$ and $9 \; cm$. The dielectric constant of the medium between them is $6$. The capacity of the condenser will be

$64$ 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 . . . . . . .

The unit of electric permittivity is

$A$ solid conducting sphere of radius $R_1$ is surrounded by a hollow conducting sphere of radius $R_2$. The capacitance of this assembly is proportional to ........

$A$ spherical capacitor has an outer sphere of radius $5 \text{ cm}$ and an inner sphere of radius $2 \text{ cm}$. When the inner sphere is earthed,its capacity is $C_1$,and when the outer sphere is earthed,its capacity is $C_2$. Then $\frac{C_1}{C_2}$ is

The 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).