Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 12.1
Students were asked the following clicker question (Classroom Performance System, einstruction.com) in the middle of their learning cycle:
Sound wave source frequency f = 1,500 Hz.
Sound wave speed v = 340 m/s (STP)
If the temperature of the air were to increase, the wavelength of the sound wave in air would:
(A) increase.
(B) remain constant.
(C) decrease.
(D) (I'm lost, and don't know how to answer this.)
Sections 30880, 30881
(A) : 25 students
(B) : 5 students
(C) : 4 students
(D) : 0 students
This question was asked again after displaying the tallied results with the lack of consensus, with the following results. No comments were made by the instructor, in order to see if students were going to be able to discuss and determine the correct answer among themselves.
Sections 30880, 30881
(A) : 31 students
(B) : 1 student
(C) : 0 students
(D) : 0 students
Correct answer: (A)
The speed v of sound waves in air at a temperature T (in Kelvin) is:
v = v_0*sqrt(T/T_0),
where v_0 and T_0 are the speed of sound waves in air at an absolute temperature T_0.
The wavelength of a wave is given by:
lambda = v*T = v/f,
where T and f are the period and frequency of the wave, respectively; both are set by the source, which is presumed to be unchanged by the increase in air temperature. Thus increasing the temperature of the air would increase the speed of sound waves, which would result in longer wavelengths.
Pre- to post- peer-interaction gains:
pre-interaction correct = 74%
post-interaction correct = 97%
Hake, or normalized gain
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