Question

if angle of incident increases angle of deviation decreases but after a certain value of angle of incident the angle of deviation increases what is that specific value of angle of incident called does this angle same for light of all collour

Answer 1

I think it's called critical angle.....

Answer 2

Between the two media, the critical angle is the angle of incidence for which the angle of refraction is 90 degree Celsius which is a optically denser medium.

When the angle of refraction is 90°C, then the angle of incidence is equal to the critical angle. The angle at which the beam enters the object is called the angle of incidence.

Here the deviation angle first increases with increasing incidence angle and then decreases.