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.
"Diffraction is the bending of waves around obstacles or the edges of an opening. Huygens' principle states every point on a wave front acts as a source of tiny wavelets that move forward with the same speed as the wave; the wave front at a later instant is the surface that is tangent to the wavelets. Dark fringes for single slit diffraction sinθ = m⋅((wavelength λ)/(width of slit W)) where m = 1, 2, 3, ..."
"Through a smaller diameter aperture, light detracts and spreads more, resulting in a less resolved image. A larger diameter aperture, light diffracts and spreads less, resulting in a more defined image."
"Light passing through one slit will have diffraction in which the waves spread out past the slit. The wider the slit, the smaller angle of diffraction, and the smaller the slit, the bigger angle. Single-slit wave diffraction can be demonstrated using three variables: the slit width (W), the spread angle (θ), and the wavelength (%lambda;). The diffraction minima equation relates the width and the spread angle to the wavelength, accounting for the initial hose example."
"I understand the concept that if the width, W, is wider, the half-angle will be smaller, and if the W is smaller, then the half-angle will be wider. The analogy of the graden hose is very helpful."
That the single slit width W has an inverse relationship with the spread angle. As width increases, spread angle decreases, and vice versa."
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 understood why a smaller value for width caused more diffraction because width is in the denominator, however I don't quite understand how the light bends around objects like a slit."
"This reading didn't present much I didn't understand. The concept seems relatively straightforward."
"I was just a little confused about the equations mentioned and how to use them and what they're used for."
"Why would the θ of diffraction get bigger as W gets smaller?"
"What I don't understand is why the spread angle gets smaller when the width gets larger. It seems to me like it would be the other way around."
"I got a bit lost in the how increasing/decreasing the width making the spread angle decrease/increase. It just seems sort of backwards to what I thought it would be."
"I don't understand the difference between angle spread and diffraction minima."
"The equations and diagrams seemed a bit confusing. Examples and equation walkthroughs in class would be helpful."
"I didn't understand the difference between the central bright fringe and the dark fringes. I also need to better understand how to find the central bright fringe (the dark fringe is the formula presented in the book and online lecture)."
Match the single slit parameter with its symbol. (Only correct responses shown.)
Width of a single slit: W [90%]
Wavelength of light passing through the slit: λ [90%]
Direction, as measured from the centerline: θ [90%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I enjoyed this reading."
"Excited to do excellently on the quiz tomorrow!"
"I found Huygens' principle confusing with its terminology of wavelets. What is a wavelet and how does it pertain to diffraction?" (In class we'll apply Huygen's principle and wavelets to explain how diffraction is analogous to how waves "wrap around corners.")
"I was kind of confused at the end of the presentation when the lab was briefly explained and states that shining a laser at a single hair is like waves traveling through a single slit... I guess I would need more explanation to figure out how that is exactly." (We'll discuss in class how waves will "wrap around" each edge of an opening and spread out, but also waves can "wrap around" each edge of an obstacle, and then cross over each other as they spread out.)
"More of a general math question: what is the physical significance of using the sine of an angle and, specifically, how is it applied for single-slit wave diffraction?" (We'll see how that sine appears when we discuss double-slit interference in much more detail in lab and in lecture.)
"Is this class going to talk about the dark matter?" (No, but we do get to talk about dark matter in my other Astronomy 210 lecture.)
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