State Huygens' principle of diffraction of light.

Explanation

Hygen's principle is besed on the following assumptions:
(i) Each point on the given or primary wavefront acts as a source of secondary wavelets, sending out distrubance in all directions in a similar manner as the original source of light does.
(ii) The new position of the wavelength at any instant is the envelope of the secondary wavelets at that instant.