Physics quiz question: increasing frequency of wave source

Physics 205A Quiz 6, fall semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Multiple-Choice Questions 11.5, 11.6

A periodic wave has a frequency and wavelength of 125 Hz and 0.60 m, respectively. If the frequency of the wave source is increased, the __________ would increase.
(A) wave speed.
(B) wavelength.
(C) (Both of the above choices.)
(D) (Neither of above choices.)

Correct answer: (D)

Wave speed v depends on the properties of the medium. Frequency f depends on the properties of the source. These two parameters can be varied independently of each other.

The wavelength λ is the parameter dependent on both of the independent parameters:

λ = v/f,

such that increasing the frequency f of a wave source will not affect the wave speed v, but will cause the wavelength λ to decrease.

Response (A) is incorrectly interpreting the mathematically correct statement:

v = λ·f,

to mean that the wave speed v depends on wavelength λ and frequency f.

Sections 70854, 70855
Exam code: quiz06w4VE
(A) : 26 students
(B) : 4 students
(C) : 0 students
(D) : 23 students

Success level: 43%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.46