Polar Dielectric in Uniform Electric Field

 i) There are permanent dipoles present in Polar Dielectric which are randomly aligned in such a way that there exists permanent dipole moment  Pp.

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

iii) Because of this all dipoles in polar dielectric are partially aligned in the direction of the field. This partial alignment is responsible for the induced dipole moment Pi.

Therefore the electric dipole moment is increasing.

P = Pp + Pi

iv) The electric dipole moment of a polar dielectric increases

      a) by increasing the applied electric field

      b) by decreasing the temperature 

What are Hydrogen Bonds?

This bond may be considered as a special type of dipole bond, but it is one that is considerably stronger. It occurs between molecules in which one end is a hydrogen atom. When a hydrogen atom is covalent bonded  to a relatively large atom such as Nitrogen, Oxygen or Fluorine a powerful permanent dipole is set up.

This is because the electron cloud tends to become concentrated around that part of molecule containing the Nitrogen, Oxygen and Fluorine Nucleus, thus leaving the positively charged Hydrogen Nucleus relatively unprotected.  

Consequently a strong permanent dipole is created that can bond to other similar dipoles with a force near that involved in the ionic bond.

 A good example of Hydrogen bond is water molecule.