Question

The critical angle for an air-glass interface is 41.8 degrees. Which of the following situations would result in total internal reflection? (a) Light incident in air at an angle of 25 degrees (b) Light incident in air at an angle of 55 degrees (c) Light incident in glass at an angle of 25 degrees (d) Light incident in glass at an angle of 55 degrees

(What I have tried to figure this out is that air has n = 1.0 and glass has n = 1.5 but have no idea how to determine where the 41.8 degrees goes and how to figure out how to get the answer)

Answer 1

The answer is option d.

Reason:

{refraction formula}

now clearly the refractive index of the glass will be 1.5.

if the light comes at angle greater than it will be reflected internally. See the second picture. Since the only option is option d where light appears at an angle 55 degrees it will be reflected internally since the critical angle is 41.8 degrees. Otherwise if it had been incident on the glass air interface at a smaller angle it would have been refracted and have gone to air.