Question

what is critical angle? who it is related with refractive index?​

Answer 1

It refers to incident angle which when project to a denser surface produces an refraction angle of 90 degrees

Ic = Critical angle = sin ^-1 (n21)

where n21 = refractive index of denser medium / refractive index of rarer medium

Answer 2

The critical angle is that angle at which, if a ray is incident while passing from a denser to a rarer medium, the angle of refraction is. ⇒ sin ⁡ i c r sin ⁡ 90 o = 1 μ where, is the critical angle, and, is the refractive index for a ray passing from the rarer to the denser medium.