Wave Optics

Huygens principle

• Every point on a given wave front (called the primary wave front) acts as a fresh source of new disturbances, called secondary wavelets.

• The surface touching these secondary wavelets tangentially in the forward direction at any instant, gives the new wave front at that instant. This is called secondary wave front.

• Using Huygen's principle we can prove the laws of reflection and and laws of refraction.

Doppler's effect of Light 

• Change in frequency of light when there is relative motion between the source of light and the observer.

• The fractional change in the frequency is found by $\frac{∆\nu }{\nu }= -\frac{v_{rad}}{c}$
   where v_rad  is radial velocity that is relative velocity of source with respect to the observer along the line …