Physics quiz question: frequency of light, given wavelength

Physics 205B Quiz 1, Spring Semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 22.13

Light has a wavelength of 600 nm as it travels through air. What is the frequency of this light?
(A) 2.0e-15 Hz.
(B) 180 Hz.
(C) 1.7e6 Hz.
(D) 5.0e14 Hz

Correct answer: (D)

The dependent parameter lambda = v/f, where the independent parameters v and f correspond to the speed the frequency, respectively. Thus f = v/lambda = (3.00e8 m/s)/(600e-9 m) = 5.0e14 s^-1, or Hz. (The speed of light in vacuum was provided, as well as the index of refraction for air n_air = 1.000.) Response (A) is lambda/v, response (B) is c*lambda, and response (C) is 1/lambda.

Student responses
Section 31988
(A) : 2 students
(B) : 0 students
(C) : 2 students
(D) : 9 students

Success level: 69%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.75