The unit of electric permittivity is

The capacitance of a spherical condenser is $1\,\mu F$. If the spacing between the two spheres is $1\,mm$,then the radius of the outer sphere is

The electric field between the two spheres of a charged spherical capacitor:

$A$ cylindrical capacitor has two co-axial cylinders of length $15 \; cm$ and radii $1.5 \; cm$ and $1.4 \; cm$. The outer cylinder is earthed and the inner cylinder is given a charge of $3.5 \; \mu C$. Determine the capacitance of the system and the potential of the inner cylinder. Neglect end effects (i.e.,bending of field lines at the ends).

$A$ capacitor of unknown capacitance $C$ is connected across a battery of $V$ volt. The charge stored in it becomes $Q$ coulomb. When the potential across the capacitor is reduced by $V^{\prime}$ volt,the charge stored in it becomes $Q^{\prime}$ coulomb. The capacitance $C$ is:

Two spherical conductors $A$ and $B$ of radii $a$ and $b$ $(b > a)$ are placed in air concentrically. $B$ is given a charge $+Q$ and $A$ is grounded. The equivalent capacitance of this system is: