## 20180221

Physics 205B, spring semester 2018
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 presentation 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 spread of light from a single slit. A smaller W (slit width) results in a larger spread angle. This spread angle is the destructive region which is the boundary of most of the diffracted wave energy."

"I understand the idea behind waves spreading after traveling through a single slit. The smaller the slit, the larger the half angle of the spread will be. Also the formula is based on the half angle."

"I understand that when the width of a slit gets smaller the 'spread' increases. And when the width of a slit gets bigger the 'spread' decreases."

"Honestly all I understood was the terminology."

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.
"Most of the presentation seemed fairly clear and to the point. I could possibly use some more clarifications on what exactly the minima angle represents and the difference between the half-angle and the minima angle."

"When reading from the book I didn't really quite get the difference between the central bright fringe and the dark fringes. I don't really understand how to find the central bright fringe whereas the dark fringe is just the formula presented in the book and online lecture."

"What the relationship between the first minima and spread angle?"

"Although I understood the relationship between W and θ, I dont know how to actually calculate that. I am sure we will go over this later."

"The laser hair screen slide was the only part of this lecture slide that was confusing, I just would need to see another example and I will probably be ok."

Match the single slit parameter with its symbol. (Only correct responses shown.)
Width of a single slit: W [97%]
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.
"I'm scared of how easy this lesson was." (Hmmm.)

"Would these calculations help when deciding where to put a harbor?" (Or designing a sound system. Or a telescope. Or anything to do with minimizing (or maximizing) the spread of water, sound, light, or any other types of waves.)

"Why do we reference a half-angle instead of the angle showed? How does squinting play a part in how well we can see?"

"Lab reports due Monday?" (Yes. Like every Monday now, for the rest of the semester.)

"To get the bonus turn-in credit for the lab reports, we have until the end of the first 10 minutes of class on next Monday? Or should we give it to you this Wednesday? (Either is fine.)

"I miss the old classroom." (I do, too; but Physics 205B usually gets put into 2401 instead of 2402, and you do not want to be in 2401 (the biology forum).)

"I honestly just raced through this because I'm in Utah trying to shovel snow, put chains on and make it back into town." (Let's see if you made it back.)

"Hey, how has your holiday weekend break? (Eh. Got a lot of things done, but still need to grade your lab reports. I'll get to them this weekend.)