Online reading assignment: standing waves

Physics 205A, fall semester 2017
Cuesta College, San Luis Obispo, CA

Students have a bi-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 waves.


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.

"Wavelength is dependent on speed and frequency. Fundamental frequency is dependent on wave speed and length. Changing the independent variables changes the dependent variables."

"Again, this is some very nice review of what I learned in high school physics. The concept of waves, periods, and frequency all make sense to me. As well as the way in which they are applied in both physics problems and everyday life."

"The speed, frequency, and amplitude of a wave are independent and can be changed without affecting each other, but wavelength is affected by speed and frequency. Natural frequency is when resonance occurs and if the string is vibrated twice the frequency, the string creates a second harmonic, a third for three and so on."

"Guitar or bass strings that are thicker resonate at a lower fundamentals frequency than thinner strings. This is because of the relationship of mass per length. A thicker string would have more mass meaning that the frequency would have to be lower if the mass was higher."

"Strings of finite length, when disturbed with a period in their fundamental frequency, experience a property called resonance. Different string thicknesses have different fundamental frequencies, which explains how plucking guitar strings makes different sounds. Fundamental frequencies are also affected by string length."

"If a string were to be plucked, it would oscillate at its fundamental frequency. If a string were periodically disturbed at the same fundamental frequency, then it would undergo resonance instead. Then if a string were oscillated at twice the fundamental frequency, then it would result in a pattern that creates a node in the center which is where we get the 'standing' in standing waves."

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.

"I'm still a little confused when the wave string speed equation and when to use the independent parameters equation when simply determining what is and isn't changing."

"I had some trouble with 'standing waves.' Could you go over this?"

"More elaboration on resonance."

"Nothing."

"I did not find anything confusing."

(Assuming that their tensions are approximately equal), the __________ strings have a slower wave speed.

thicker.	*********************************** [35]
thinner.	** [2]
(There is a tie.)	*** [3]
(Unsure/lost/guessing/help!)	** [2]

After these same-length guitar strings are plucked (assuming that their tensions are approximately equal), the __________ strings vibrate at a lower fundamental frequency.

thicker.	**************************** [28]
thinner.	**** [4]
(There is a tie.)	****** [6]
(Unsure/lost/guessing/help!)	**** [4]

After the bass string is plucked, sliding a finger down to decrease its length would __________ the speed of waves along the string.

decrease.	******* [7]
not change.	**************** [16]
increase.	***************** [17]
(Unsure/lost/guessing/help!)	** [2]

After the bass string is plucked, sliding a finger down to decrease its length would __________ the fundamental frequency of the string.

decrease.	************ [12]
not change.	******** [8]
increase.	***** [20]
(Unsure/lost/guessing/help!)	** [2]

For standing waves on a string, 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.)

Wave speed v: independent [50%]
String length L: independent. [62%]
Fundamental frequency f₁: dependent. [55%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"This reading was very confusing to me."

"Can you explain how string thickness affects speed? I am looking at the formula for a (standing wave) string fixed on both ends and I don't see the math."

"It's cool how these things relate to music."

"I now understand wave parameters better due to the examples we did in class. That was helpful."

"Haven't had as much time as I'd like to review last Wednesday's lecture, but wanted to mention that I am appreciative of the format of this course. Despite how fast-paced it is, I feel the previews of the blog and the repetition involved with the sample questions (initial exposure before the lecture, seeing them worked out during lecture, and trying them again in the post-lecture) is very helpful in cementing understanding. These are the sort of study techniques that are often advised, but I have usually dismissed them as overkill. Being required to follow through has been very conducive to my understanding of this material."

"I have nothing interesting to say :/" (Sometimes that's just the way it is.)

"Do you play an instrument? (In grade school, we learned how to play the most played instrument ever in history.)