Two parallel plates of area $A$ are separated by two different dielectric as shown in figure, Fig.$4.106$ . The net capacitance is

 A parallel plate capacitor with air as the dielectric has capacitance $C$ A slab of dielectric constant $K$ and having the same thickness as the separation between the plates is introduced so as to fill one-fourth of the capacitor as shown in figure. The new capacitance will be

Each capacitor shown in is$2\mu \mathrm{F}$. Then the equivalent capacitance between points $A$ and $B$ is

The work done is placing a charge of $8\times {10}^{-18}$ coulomb on a condenser of capacity $100\mu \mathrm{F}$ is