20130226

Online reading assignment: double-slit interference

Physics 205B, spring semester 2013
Cuesta College, San Luis Obispo, CA

Students have a 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 double-slit interference.

Selected/edited responses are given below.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"I found Thomas Young's experiment very interesting. I liked this experiment, because it reminds me of one done on electrons, and how those act. I know that this is kind of unrelated, but it is based on how the electrons behave when shot through two slits just like the light experiment."

"I thought it was really neat how Thomas Young was the first person to be able to measure the wavelength of light by using a double slit experiment."

"I found that maxima is the location were two sources interfere constructively, and minima is the same definition, but where destructive interference occurs."

"Nothing because I don't understand how this information applies to anything."

"The idea of light waves canceling is weird, but I like that. I like the real world example of water waves."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I was having trouble understanding why the light that comes out of the two slits starts in phase but ends up being out of phase."

"I don't think Young's experiment could be written any more confusingly than in the book."

"Where those waves from the double slit are constructive or destructive as theta increases."

"How ∆l = d·sinθ."

"This section doesn't seem too hard to grasp."

"I am confused on all of this. Could use some explanation in class not solely inclusive of problem-solving."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I don't understand for waves from a double-slit how the rays converge to one point. Why are they not constantly parallel from the beginning?" (They can't be parallel if they are to eventually meet at the same location. But if that location is very far away, and the space between the two slits is relatively small, then the two rays can be said to be approximately parallel.)

"Sometimes the animated slides can be more confusing then if they weren't animated. they may be a bit to fast to read and comprehend before the animation changes." (Well, it's a compromise between being too slow, and waiting a long time to see what happens, and being too fast, and not being able to see each step. At least the animations loop continuously.)

"I got a little off-topic and side-tracked while reading when I came across the image of a cross-section of a CD. Not very much of it made sense. Could we possibly go over this in class briefly? Just interested in how it really works with the 'pits' in the reflective layer." (The bumpy concave/convex "pits" scatter laser light in all directions, while the flat "land" portions will reflect laser light back to the detector for a standard CD-ROM. The length and spacing of the both the "land" and "pit" portions that encode binary data.)

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