## 20141117

Physics 205A, fall semester 2014
Cuesta College, San Luis Obispo, CA

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing a presentation on sound.

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"The frequency of a sound wave is set by the source as it vibrates the air in front of it. The speed of a sound wave in air depends approximately on the square root of the absolute temperature."

"Wavelength is dependent on two independent factors, velocity and frequency. The fundamental frequency in pipes depends on velocity and length."

"In some regions of sound waves there are compressions and rarefactions. Compressions are where molecules are tight together causing a higher pressure, and rarefactions are where molecules are spread out and have a lower pressure."

"Transverse waves on materials do not make sound waves by themselves but do cause them by exciting the air around them."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"How there can be a standing sound wave. Nor do I understand the formulas that go with it."

"I'm going to wait for the lecture to figure out what I know and what I don't."

"The difference between the independent and dependent parameters."

"What I don't quite understand is what we are learning."

For sound waves, what does the T for sound wave speeds stand for, and what is its SI (Système International) unit?
"Absolute temperature, measured in K (kelvins)."

"T is the period of the wave. The inverse of T, called the frequency, is measured in Hertz."

For sound waves in air, classify each of these parameters are being "independent" (able to be changed without affecting other independent parameters), or "dependent" (will be changed when independent values are changed).
(Only correct responses shown.)
Amplitude A: independent [63%]
Wave velocity v: independent [55%]
Frequency f: independent [60%]
Wavelength λ: dependent [73%]

For sound waves in a tube, classify each of these parameters are being "independent" (able to be changed without affecting other independent parameters), or "dependent" (will be changed when independent values are changed).
(Only correct responses shown.)
Sound wave velocity v: independent [45%]
Tube length L: independent [50%]
Fundamental frequency f1: dependent [62%]
Frequency f of sound "blown" into tube: independent [50%]

Select the standing sound waves that would resonate in the tubes below.
(Only correct responses shown.)
Tube open at both ends: all multiples of f1 [57%]
Tube open at one end, and closed at the other end: only odd multiples of f1 [65%]
Tube closed at both ends: all multiples of f1 [53%]

What musical instrument(s) do you play? List none, or as many as applicable. #justasking
"None." [15 responses]

"Guitar." [10 responses]

"Piano." [10 responses]

"Singing." [3 responses]

"Flute." [2 responses]

"Saxophone."

"Violin/viola." [3 responses]

"Ukulele."

"Tuba."

"French horn."

"Banjo."

"Clarinet."

"Didgeridoo."

"Tumbak and jembek."

"Trumpet." [2 responses]

"Trombone." [2 responses]

"Drums/percussion." [3 responses]

"Bass/bass guitar." [3 responses]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Why do resonant frequencies of asymmetrical pipes only occur in odd multiples?" (Because they have mismatched ends--one open, one closed--so all possible symmetric standing waves, which are the even multiples of the fundamental frequency, are not allowed, and only odd multiples are allowed.)

"What musical instrument(s) do you play?" (Piano, ukulele, and in grade school, the most played instrument in 20th century.)