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.
"The principle of linear superposition, states that the resultant disturbance is the sum of the disturbances from the individual waves, which can be constructive or destructive interference."
"Two waves combine when they arrive at the same point. They reinforce each other during constructive interference or cancel each other through destructive interference."
"If two waves constructively interfere, their crests and troughs line up creating a bigger wave. In contrast, if two waves destructively interfere, the crests and troughs are contrary and they cancel out each other. Also whether two waves are constructive or destructive not only depends on the source phases of the waves, but also on the path length difference."
"I like how visual this lecture was. It seemed much easier to comprehend seeing the waves and the differences in their peaks and troughs which then made it easier to understand that when they align they are constructive and when they do not they are destructive."
"In phase sources result in constructive interference and out of phase sources result in destructive interference. For two in phase sources, if one wave travels a whole wavelength longer than the other, then constructive interference occurs; if instead one wave is a half wavelength longer than the other, then destructive interference occurs. Out of phase sources have an opposite result."
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.
"The mathematical equations regarding the conditions; I would like those to be explained in-depth."
"The equations are confusing. Applying things to the diagrams needs more elaboration."
"This section is pretty straightforward."
"No questions today but I think I am going to like this section."
"I think I understand this section but I feel like I'm missing something."
1: in phase sources [85%]; whole wavelength path difference [62%]; constructive [91%]
2: in phase sources [35%]; half wavelength path difference [74%]; destructive [85%]
3: in phase sources [76%]; whole wavelength path difference [71%]; constructive [85%]
4: out of phase sources [79%]; whole wavelength path difference [38%]; destructive [85%]
5: out of phase sources [35%]; half wavelength path difference [71%]; constructive [79%]
6: out of phase sources [82%]; whole wavelength path difference [62%]; destructive [88%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I need to better understand the source phase and path length differences. I will go over the presentation preview to better understand when a wave is considered to be constructive or destructive when the sources are out of phase."
"Okay, it was going smoothly up until the in phase and out of phase questions."
"I am not so sure about in phase vs out of phase sources so some clarification on that would be helpful."
"I'm a little confused on constructive/destructive differences. How can waves be in phase when one travels one-half of a wavelength longer than the other? I think I've only half got this concept down." ("In phase" or "out of phase" refers to how the two waves start off in relation to each other; either they both start off making crests (or troughs) together, so these two sources are said to be "in phase" with each other (regardless of how their waves travel after that); or one source makes a crest while the other source makes a trough (or vice versa), so these two sources are said to be "out of phase" with each other (regardless of how their waves travel after that).)
"I love the double-slit experiment! To me it's where what we think we know about the universe really starts to lose footing!" (We'll get there next week. #toosoon.)
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