Let us derive the relation between polarization vector (P), displacement (D) and electric field (E):
In the last article of polarization, we have discussed about the effect on dielectric placed in an external electric field E0 and there will be electric field due to polarized charges, this field is called electric field due to polarization (Ep). (You can see the figure in that article).
Rewrite equation (1) of that article, that is:
E = E0 – Ep (1)
Polarization vector, P = P is equal to the bound charge per unit area or equal to the surface density of bound charges (because surface charge density is charge per unit area),