A parallel plate capacitor having a plate separation of $2 \mathrm{mm}$ is charged by connecting it to a $300 \mathrm{V}$ supply. The energy density is

$A$and $C$are concentric conducting spherical shells of radius $a$and $c$, respectively. $A$is surrounded by a concentric-dielectric medium of inner radius $a,$outer radius $b$and dielectric constant $k.$If the sphere $A$is given a charge $Q,$the potential at the outer surface of the dielectric is

Two metallic bodies separated by a distance $20 \mathrm{cm}$ are given equal and opposite charges of magnitude $0.88 \mathrm{\mu C}$ . The component of the electric field along the line $\mathrm{AB}$, between the plates, varies as to $E_x=3x^2+0.4 \mathrm{N} {\mathrm{C}}^{-1}$, where $x$ (in meters) is the distance from one body towards the other body as shown.

If each capacitor is of capacity $C$, find the capacitance between $A$ and $B$.

Four condensers are joined as shown in the adjoining figure. The capacity of each is $8 \mathrm{\mu F}$. The equivalent capacity between the points $A$ and $B$ will be