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 diffraction.
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 when you decrease the size of W, then the theta or spread increases, and visa versa, increasing W would lead to a more narrow spread, which helps with telescopes. I also understand how waves can bend around the edges of the slit, not just shining directly through."
"Diffraction is the bending of light waves around obstacles or edges of an opening. As light moves through a slit, it will result in an angle that will vary depending on the size of the opening. As the W (width) of the slit increases in size, the angle of light expelled decreases. As W decreases, the angle will increase."
"Diffraction is the bending of waves around obstacles. I also understand that the degree of bending in light is much less than in sound."
"The diffraction minima is given by W·sinθ = m·λ where W is the width of a single slit, θ is the angle of the spread from the center, and λ is wavelength of light."
"Diffraction is how light is perceived and bends through a slit. What is important is how large the wave length is and what the angle it is exiting from the slit at compared to the 'normal.' As the slit increase, the minima angle decreases and vice versa. When talking about telescopes, they use a large width so the angle must be small to resolve details of far-away objects."
"Essentially, decreasing slit width W causes an increase in the 'spread' of the half-angle θ. Conversely, increasing slit width would produce the opposite effect onto the spread of θ."
"The slit width and analogies were perfect. The example in the ocean with the waves is both a pun and a great example! "
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 dark fringes for single-slit diffraction was confusing to me."
"I guess I didn't really understand what a slit is."
"I am confused about how to find the minima angle. I am also unsure of where it comes in and if it is only with destructive interference."
"I was confused about the midpoint of a central bright fringe. I did not understand what that had to do with the destructive interference. "
"What is the difference between spread angle and diffraction minima?"
"I am slightly confused as to what effects the relationship of slit width and spread of theta cause. Looking at the telescope example, I believe I understand the idea that a larger slit with produces a smaller theta causing less spread and a more refined image."
"I'm not understanding the diffraction of light through the telescope, and the hair laser example."
"Not much really. A few examples and minor explanation should get me up to speed."
"I didn't find anything confusing about this topic. "
"Honestly just haven't got to this yet."
Match the single slit parameter with its symbol. (Only correct responses shown.)
Width of a single slit: W [94%]
Wavelength of light passing through the slit: λ [97%]
Direction, as measured from the centerline: θ [97%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"May you explain the textbook diagrams in class? The textbook's diagrams and graphs made the concept more difficult."
"Light without diffraction would pass straight through a narrow slit without spreading out?"
"By making the slit width larger and larger does there reach a point where making the slit larger would result in an inconsequential reduction in the spread of the diffracted waves?" (Yes. If the slit were large, then diffraction (the "wrapping around the edge effect") would be less noticeable, and the light would not seem to spread out much, so the beam would have the same size/shape as the slit. If the slit were very small, then the "edge effect" would be more noticeable, and the light will spread out more such that the beam would "fan out.")
"What is the m referring to in the equation sinθ=m·λ/W), as explained by the textbook? Will there ever be a time when m will be more than 1?" (Yes, in order to find the fainter dark fringes off to the side of the "spread angle" (where m = 1), but we'll only concentrate on the light contained within the m = 1 "spread angle," because that's where most of the spread-out light is concentrated after passing through the slit.)
"I was curious as to what happens when two slits are close to each other. Can they have constructive interference?" (Yes, provide that each slit is small enough that light will spread out (diffract) so they will overlap with each other, and then can interfere with each other.)
"I am glad you're my professor. My other class I felt so lost the whole time but this semester I don't."
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