Light is traveling in a particular optical medium probably s

Light is traveling in a particular optical medium (probably some type of plastic) and is incident on an interface with air.

When the incident angle is exactly equal to the critical angle, what is the angle of refraction?   ^o
The critical angle is measured to be 38.9^o. Calculate the refractive index of this medium. (THREE SIGNIFICANT FIGURES)

Solution

When the angle of incidence in water reaches a certain critical value, the refracted ray lies along the boundary, having an angle of refraction of 90-degrees. This angle of incidence is known as the critical angle; it is the largest angle of incidence for which refraction can still occur. For any angle of incidence greater than the critical angle, light will undergo total internal reflection.

Now sine(_crit) = n_r/n_i

   sin38.9 = 1/n_i

     n_i = 1/ sin38.9 = 1.592