n being the number of molecules per unit volume i.e. 
is the dipole moment per unit volume. Let us now consider a dielectric material having polarization and compute the potential at an external point O due to an elementary dipole dv'.
Fig 2.16:
Potential at an External Point due to an Elementary Dipole dv'.
With reference to the figure 2.16, we can write: 
..........................................(2.60)
Therefore,
........................................(2.61)
........(2.62)
where x,y,z represent the coordinates of the external point O and x',y',z' are the coordinates of the source point.
From the expression of R, we can verify that
.............................................(2.63)