## 20191202

### Online reading assignment: standing waves

Physics 205A, fall semester 2019
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 standing 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.
"Thick strings have lower fundamental frequencies than thinner strings when they are plucked."

"I understand that the fundamental frequency of a string depends on the wave speed v (which depends on its tension and thickness), and length L. The frequencies that this string will resonate at are then merely integer multiples of the fundamental frequency."

"What I understand is some of the standing waves stuff. I know the equation for getting the fundamental frequency of something. I also understand which things are independent and dependent parameters."

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 feel like this is more in depth of the previous waves section, this feels similar and not difficult, just more of it."

"Putting all the different parts together, and not mixing up the independent and dependent parameters."

"I'm having trouble understanding resonance and how nodes are created."

"The difference between node and antinode wasnt as clear to me. Will need some more clarification in class."

(Assuming that their tensions are approximately equal), the __________ strings have a slower wave speed.
 thicker. ************************************** [38] thinner. *** [3] (There is a tie.) ** [2] (Unsure/lost/guessing/help!) * [1]

After these same-length guitar strings are plucked (assuming that their tensions are approximately equal), the __________ strings vibrate at a lower fundamental frequency.
 thicker. ************************************ [36] thinner. ** [2] (There is a tie.) *** [3] (Unsure/lost/guessing/help!) *** [3]

After the bass string is plucked, sliding a finger down to decrease its length would __________ the speed of waves along the string.
 decrease. ****************** [18] not change. ******** [8] increase. ***************** [17] (Unsure/lost/guessing/help!) * [1]

After the bass string is plucked, sliding a finger down to decrease its length would __________ the fundamental frequency of the string.
 decrease. *********** [11] not change. ********* [9] increase. ********************** [22] (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 [59%]
String length L: independent. [43%]
Fundamental frequency f1: dependent. [50%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"May we focus on the fundamental frequencies? I did not understand the equation."

"Go over deez."

"Is there a particular reason we left waves and then came back to them later?" (We lost a Monday due to Veteran's Day, so we'll pick it up here just before you do the standing waves lab later today. Also this stuff is not on Quiz 6 or on Quiz 7, but you'll see it on the Final Exam.)

"How was your Thanksgiving?" (Eh, it was okay. The day after Thanksgiving went much better.)

"I'm full from the turkey."