What are polar molecules, Explain?

Explain the behaviour of dielectrics in an external field.

The capacity of a parallel plate capacitor with air is $18 \mathrm{pF}$ When a dielectric material is inserted in the space between the plates, its capacity becomes $108 \mathrm{pF}$.Calculate the permittivity of the material. What is the material?(${\mathrm{\epsilon }}_0=8.854\times {10}^{-12}{\mathrm{C}}^2{\mathrm{N}}^{-1}{\mathrm{m}}^{-2}$)

What is a capacitor? You know that the capacity of a parallel plate condenser is $C=\frac{{\epsilon }_0 A}{d}$. What will be its new capacitance $C\text{'}$ of the capacitor if a material of dielectric $K$ is inserted between the plates? Calculate the capacitance of the capacitor shown below.