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 presentations Feynman diagrams (Phillip "Flip" Tanedo, Cornell University/USLHC Collaboration) and quantum electrodynamics (QED) (Christopher "Bot" Skilbeck, cronodon.com).
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.
"The lines with arrows are matter particles. The wiggly line is a force particle which mediates electromagnetic interactions: it is the photon."
"Mostly just the basics of a Feynman diagram. The x-axis represents time and the y-axis represents direction. A straight line with a right-facing arrow is an electron, and straight line with a left-facing arrow is a positron, and a squiggly line is a photon. You can connect the straight lines as long as they also connect to a squiggly line, and all the pieces in a diagram have to be connected in some way, and there can't be any excess curves."
"Squiggles..."
"I'm fairly lost at this point."
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.
"What I found confusing about this reading was trying to apply the chemistry to these diagrams that we are reading about. I can understand how these diagrams help explain decay sequences of particles. But I am just really trying to figure how I can draw one of these things for an actual reaction/decay. Also, I am starting to study for our midterm this upcoming Friday and I am still catching up with all of the magnetic stuff we've been talking about in class so I just really can't focus on this stuff, yet."
"I don't quite get all the rules for how to read the diagrams. More explanation on that would be great."
"Basically everything except the basics of the Feynman diagrams. I was horribly deceived into thinking that I would actually understand this stuff by the sentence near the beginning of the first post: "Particle physics: fun for the whole family.' Yeah right."
"I do not understand what 'annihilated by positron' is."
"What are we going to be applying this in class for? It's scary to ponder."
When reading Feynman diagrams, time runs from:
bottom to top. * [1] top to bottom. [0] left to right. ******************************** [32] right to left. * [1] (Unsure/guessing/lost/help!) *** [3]
Describe how the path of an electron and the path of a positron are drawn differently on a Feynman diagram. (Note that both paths have the same "e" labels.)
"The path of an electron is drawn with its arrow pointing to the right, while the path of a positron is drawn with its arrow pointing to the left."
"I thought it was labeled e+ and e- for positron and electron respectively, but it would appear it can be labeled depending on the arrows as well."
"Not sure."
Describe what will happen if an electron meets a positron.
"They annihilate each other and produce energy?"
"They will annihilate each other and produce a photon."
"Boom! There goes the gamma ray."
absorbing a photon. * [1] emitting a photon. ******************************** [32] annihilated by a positron. ** [2] (Unsure/guessing/lost/help!) ** [2]
absorbing a photon. ***** [5] emitting a photon. ****** [6] annihilated by a positron. ************************ [24] (Unsure/guessing/lost/help!) ** [2]
absorbing a photon. ************************** [26] emitting a photon. ****** [6] annihilated by a positron. ** [2] (Unsure/guessing/lost/help!) *** [3]
"Two elections do not form a photon. An electron can only emit a photon and then keep going."
"It says that two electrons come together to produce a photon which is (I hope) impossible."
"It violates rule number 2: 'You must have exactly one arrow going into the vertex and exactly one arrow coming out.'"
"I'm not really sure."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I only understood about 50% of the reading. Is that bad?"
"Seriously, can school be over?!?"
"I am freaking out a bit for the exam. Some of the material looks like from forever ago(?) and I have a calculus exam just before the physics exam. Trying not to have a panic attack."
"If we could just work on some review for the midterm, that'd be tight."
"Review pleassseeeee!"
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