Physics quiz question: speed of light in melted butter

Physics 205B Quiz 1, spring semester 2014
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Question 23.7

Light in air (index of refraction 1.000) passes into melted butter (index of refraction[*] of 1.45) with an incident angle of 60.0°. (Drawing is not to scale.) The speed of light in melted butter is __________ the speed it has in air.
(A) slower than.
(B) the same as.
(C) faster than.
(D) (Not enough information is given.)

[*] physics.info/refraction/.

Correct answer (highlight to unhide): (A)

The relationships between the index of refraction and speed of light in a given medium are:

n_air = c/v_air,
n_{melted butter} = c/v_{melted butter}.

Since the index of refraction for air is 1.000, the speed of light in air essentially nearly identical to that in vacuum, c. Since the index of refraction for melted butter is greater than that of air, then the speed of light through melted butter must be slower than that in air.
Sections 30882, 30883
Exam code: quiz01ksB4
(A) : 41 students
(B) : 0 students
(C) : 0 students
(D) : 0 students

Success level: 100%
Discrimination index (Aubrecht & Aubrecht, 1983): 0