## 20180214

### Online reading assignment: interference

Physics 205B, spring semester 2018
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 presentations on interference.

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.
"When two light waves arrive the same point they combine. they can reinforce each other during constructive interference, or cancel each other through destructive interference."

"With constructive interference the waves are in sync and reinforce each other and with destructive interference the waves cancel each other out. There are also different types of source phases and path length differences that can affect whether a wave is constructive or destructive."

"I understand that when sound waves troughs and crests line up (move in unison) there is constructive interference. On the other hand, when the troughs and crests don't line up (out of unison) there is destructive interference."

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 found distinguishing between in phase and out of phase sources slightly confusing. I'm not entirely sure whether a wave is considered to be constructive or destructive when the sources are out of phase. I just need some examples and I think I'll be able to figure it out."

"I don't understand the source phase and path length differences."

"I don't understand how to determine the path length differences."

"I have a good understanding of this material. Maybe some in-class examples of constructive and destructive interference would be helpful."

"I didn't find anything really confusing this lesson."

Classify the various interfering wave examples. (Only correct responses shown.)
1: in phase sources [92%]; whole wavelength path difference [96%]; constructive [92%]
2: in phase sources [63%]; half wavelength path difference [96%]; destructive [92%]
3: in phase sources [83%]; whole wavelength path difference [83%]; constructive [92%]
4: out of phase sources [83%]; whole wavelength path difference [67%]; destructive [88%]
5: out of phase sources [42%]; half wavelength path difference [63%]; constructive [83%]
6: out of phase sources [92%]; whole wavelength path difference [42%]; destructive [88%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Are you enjoying the Olympics?" (Only while watching Mrs. P-dog's cousin compete in slopestyle and big air snowboarding.)

I think I got these diagrams...but sometimes I think I understand something and it later turns out that I'm entirely wrong."

"Lab due next Monday?" (No school next Monday. So, they're due next next Monday.)