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.
"I understand that if two sound speakers are wired the same, then they will be in phase which results in constructive interference and the sound will be louder. If they are not wired the same, then they will be out of phase which results in destructive interference and a more quiet sound."
"If two waves are in phase and have a whole length difference, they will produce constructive interference. If the waves are out of phase or have a half wavelength difference, destructive interference is produced."
"The principle of linear superposition states that the resultant disturbance is the sum of the disturbances from the individual waves. I also understand that interference alters the brightness of light and loudness of sound."
"This paragraph from the presentation helped me understand the basics: 'Here we have two speakers, which are our sources of two sound waves. Since they are plugged into the same frequency source, they will generate sound waves of the same frequency f (which is depends only on the source), same speed v (which depends only on the medium), and thus the same wavelength λ (which depends on both f and v). If the speakers are wired the same way--red and black wires to red and black plugs--then they will oscillate in phase, with both speaker cones moving forward and backwards in unison.'"
"I understood the in-phase and out-of-phase part, and how to tell the difference. I also understood what is constructive and destructive."
"The way two wave sources are emitted determines whether the resulting wave will be constructive or deconstructive. In-phase waves have the same velocity, wavelength, and frequency, also in-phase waves are traveling in the same direction and can form a constructive of bigger resulting wave. Out-Phase waves do not align crest to trough and they do not have the same velocity, frequency or wavelength and the resulting wave is smaller or no wave."
"My primary take-away from this set of slides is the difference between constructive interference (music playing from the neighbor's stereo), and destructive interference (silence, or quieted volume). When the crests and troughs of the two wavelengths line up, constructive interference occurs; however, if those wavelengths are not aligned, destructive interference takes place."
"There was not much that I understood from this presentation."
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 need a little more detail about when the interfering wave examples have a whole wavelength path length difference or half-wavelength path length difference."
"Completely grasping the constructive/destructive conditions flowchart."
"I found the flowchart of constructive/destructive conditions to be overwhelming especially because I don't fully understand the solid lines vs. the dashed lines. I could also use a bit of clarification on what path difference is."
"I would like a little more understand on phase differences. As well as how path length difference works."
"At first, the path length difference was confusing to understand because I did not comprehend the equations. However, after seeing some visual examples, I now understand and can observe whether a wave will be constructive or destructive."
"The difference between constructive and destructive seemed confusing. Its relationship with waves was easier to understand with the diagrams."
"I found a lot confusing with these concepts. I don't understand the difference between constructive and destructive waves. I also don't how changing the distance makes the two so different. I am also confused what they are considered when the waves are in unison, but the distance is changed."
"How does this work for radio waves? Please give examples of constructive, destructive and non-coherent sources. The book only uses visible light as an example."
"This isn't very confusing to me."
1: in phase sources [91%]; whole wavelength path difference [74%]; constructive [97%]
2: in phase sources [14%]; half wavelength path difference [86%]; destructive [89%]
3: in phase sources [86%]; whole wavelength path difference [77%]; constructive [89%]
4: out of phase sources [86%]; whole wavelength path difference [40%]; destructive [94%]
5: out of phase sources [23%]; half wavelength path difference [49%]; constructive [86%]
6: out of phase sources [89%]; whole wavelength path difference [54%]; destructive [97%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Finally lenses are over. I don't wear glasses so it was a difficult set of chapters." (I'm not so sure that this topic was any easier for student who do wear corrective optics.)
"When you change the volume on a stereo how is more sound produced? Are more sound waves generated?" (Well, "more" in the sense that the speaker cone moves in and out with a larger range of motion (larger amplitude), so more air is pushed in and out, and a greater range of pressure fluctuations result.)
"What does m stand for in the constructive/destructive conditions equation?" (Any whole positive/negative number (0, ±1, ±2, etc.).)
"Why in the world could I not find anything about path length differences?"
"May we review situation #5 specifically?"
"I just need a brief discussion about these ideas and I think I will be good on this topic."
"The wave interference problems don't seem too difficult, just need some practice."
"In that case given the two sources had the same total length and each crest and trough matched, I assumed there would be no length difference; yet, that was not an option?" (A case where there is no path length difference is the covered under the case of having a path length difference of a whole (number) of wavelengths, in this case the whole number would be zero.)
"If two sound waves are not exactly a half-wavelength off from each other, would there still be destructive interference?" (Yes, but they would not completely cancel each other out. The resulting loudness would be quieter than a single wave, but not completely quiet.)
"Will we be using noise-canceling headphones?" (That is a great application of destructive interference, but no. You can always purchase a set for yourself, though.)
"I was confused about coherent and non-coherent light sources of light. What makes a laser coherent compared to light bulbs which are incoherent?" (Basically, the light from a laser has a constant amplitude, single wavelength that starts off with a definite phase, while light from an incandescent bulb is a range of different wavelengths that can vary in amplitude and phase. It's a bit more complicated than that, but for our purposes we'll start from this working definition.)
No comments:
Post a Comment