Physics quiz question: diamond-air interface total internal reflection?

Physics 205B Quiz 1, spring semester 2018
Cuesta College, San Luis Obispo, CA

Light with an incident angle of 44.8° in diamond strikes the interface between diamond (index of refraction[*] 2.418) and air (index of refraction 1.000). (Drawing is not to scale.) As measured from the normal, the angle of the transmitted ray in air is __________ 44.8°.
(A) less than.
(B) equal to.
(C) greater than.
(D) (There is no transmitted ray in air.)

[*] physics.info/refraction/.

Correct answer (highlight to unhide): (D)

The critical angle for light incident on a diamond-air interface is given by:

θ_c = sin^–1(n₂/n₁) = sin^–1(1.000/2.418) = 24.43°.

Since the incident ray in diamond has an angle greater than the critical angle, it is totally internally reflected back into diamond, and thus there is no transmitted ray in air.)

Student responses
Sections 30882, 30883
Exam code: quiz01AM0l
(A) : 2 students
(B) : 0 students
(C) : 8 students
(D) : 25 students

Success level: 71%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.45