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
where vrad is radial velocity that is relative velocity of source with respect to the observer along the line …
To view the complete topic, please