Polar Dielectric in uniform electric field

There are permanent dipoles present in polar dielectric which are randomly aligned in such a way that there is permanent dipole moment Pp. [see fig a]

 
When a dipole is present in an uniform electric field the dipole tries to align itself in the direction of electric field.

Because of this all dipoles in a polar dielectric are partially aligned in the direction of field. This partial alignment is responsible for the induced dipole moment Pi.[see fig b].                 
Therefore, the electric dipole moment is increasing.   

P =  Pp + Pi

The electric dipole moment of a polar dielectric increases
a) by increasing the applied E.
b) by decreasing the temperature