when refraction does not cause when incident ray is normal to a interface

Asked by firdoustantray98 | 2nd Mar, 2021, 06:52: PM

Expert Answer:

Cause of refraction is explained by considering light as plane wave. When a wave starts from source it is spherical in shape .
After travelling long distance , if we consider part of spherical wave, it becomes plane wave.
 
When plane wave makes oblique incidence as shown in left side figure all parts of wavel front are not moving in same medium.
As shown in figure,  point A of wavefront reaches refracting medium earlier than point B . Hence point A will move in
refracting medium with slow speed , whereas point B will move faster from B to D .
This makes the wavefront to turn and refraction takes place.
 
In normal incidence ,  as shown in right side figure , all parts of wavefront reaches the refracting medium simultaneously.
Hence all parts of wavefront has same speed at any instant in refracting medium .
Hence there is no turning effect and hence no deviation or refraction

Answered by Thiyagarajan K | 2nd Mar, 2021, 09:52: PM