4) What is the critical angle for a light ray traveling in water with a refractive index of 1.33 that is incident on the Surface of water above which air is with a refractive index of 1.00?

The critical angle for a light ray traveling 36.9°

Explanation:

The critical angle for a light ray traveling is calculated by

apply Brewster angle tanθ = nb / na

where, nb is refractive index of surface

            na is the refractive index of water

tan θ = 1.00 / 1.33

tan θ = 0.7519

θ = 36.9°

Therefore, the critical angle for a light ray traveling 36.9°