What is polarisation?

(N/A) Polarisation is the process in which the positive and negative charges of a non-polar molecule or atom are displaced in opposite directions by an external electric field.
When a dielectric material is placed in an external electric field $E_0$, the centers of positive and negative charges are shifted.
This results in the formation of induced dipole moments within the material.
The net dipole moment per unit volume is known as the polarisation density or simply polarisation, denoted by $P$.
Mathematically, $P = \chi_e E$, where $\chi_e$ is the electric susceptibility of the dielectric material.