Online reading assignment: Feynman diagram vertices

Physics 205B, spring semester 2018
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).

The Big Bang Theory (Pilot)
Warner Bros. Television (2007)
bigbangtheory.wikia.com/wiki/User_blog:Sheldon_Cooper_PhD/Pilot

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.

"Feynman diagrams are used to describe the interactions between electrons and positrons. The interactions of electrons and positrons can resulting in absorbing a photon, emitting a photon, or a electron being annihilated by a positron."

"Lines in these diagrams represent particles. Every particle has to meet at an intersection that is called an interaction. You can't have a vertex with only squiggly lines (photons) with no particle lines flowing into or out from it."

"Feynman diagrams are how we can visualize particle physics, specifically the interactions of electrons, positrons, and photons. We read the diagrams left-to-right, as they are a representation of what happens over a certain amount of time."

"The Feynman diagrams are meant to indicate the path that the particles take through space. We interpret the x-axis as the direction of time and the y-axis as the space direction."

"A left-to-right arrow is an electron, the opposite is a positron and a wiggly line is a photon. the rest is very vague and I need more explanations on various cases and what they mean."

"Positrons point to the left, electrons point to the right. Gamma (squiggly line) are photons. A Feynman diagram should only contain connected pieces, and any diagram with arrows going into a gamma needs arrows coming out or else it isn't an accurate diagram."

"Honestly, there wasn't much I understood."

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.

"Everything. I don't get Feynman diagrams."

"Why do we use Feynman diagrams? They just seem like squiggles a 3 year-old could draw, why is there not another way to represent these forces interacting?"

"Is an electron moving in the opposite direction a positron? What actually is a positron?"

"All good so far."

"Specifically how the diagrams are to be used."

"I don't think I would really be able to interpret them on my own. It would be helpful to do this in class."

"This is all pretty trippy. I want to learn more about what diagrams are possible and which are not."

When reading Feynman diagrams, time runs from:

bottom to top.	[0]
top to bottom.	** [2]
left to right.	******************* [19]
right to left.	* [1]
(Unsure/guessing/lost/help!)	**** [4]

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.)

"Electrons point right and positrons point to the left."

"A position is indicated as e+ therefore, the electron will always be drawn traveling from right to left. Meanwhile, an electron is indicated by an e- and will always be drawn traveling left to right. This way, when they are being read, we can see that the arrows are point in the direction of the flow of electron charge."

"Positrons (antimatter) point to the left, electrons point to the right."

Describe what will happen if an electron meets a positron.

"Annihilation will happen."

"They will cancel each other out and create pure energy."

"They make a big bang!"

"It becomes something else (the other symbol thing)?"

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	*** [3]
emitting a photon.	******************* [19]
annihilated by a positron.	* [1]
(Unsure/guessing/lost/help!)	*** [3]

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	*** [3]
emitting a photon.	***** [5]
annihilated by a positron.	************** [14]
(Unsure/guessing/lost/help!)	**** [4]

The above (valid) Feynman diagram depicts an electron:

absorbing a photon.	***************** [17]
emitting a photon.	* [1]
annihilated by a positron.	**** [4]
(Unsure/guessing/lost/help!)	**** [4]

Explain why the above Feynman diagram is invalid.

"Two arrows are going into the vertex. One needs to be going out."

"The two electrons cannot intersect at the same point how this one is depicted."

"The two electrons cannot crash like that."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"What are all these squiggles and arrows about?"

"A very basic lecture on what every symbol is called and what happens when they mix would be of great benefit."

"My mind is blown.:

Astronomy current events question: Mars Express software upgrade

Astronomy 210L, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

News release, "Mars Express 2.0" (April 11, 2018)
esa.int/Our_Activities/Operations/Mars_Express_v2.0

The European Space Agency's Mars Express spacecraft will undergo a software upgrade to:
(A) reformat memory.
(B) increase photo resolution.
(C) conserve battery power.
(D) fully extend its solar panels.
(E) reduce gyroscope wear.

Correct answer: (E)

Student responses
Sections 30679, 30680
(A) : 4 students
(B) : 6 students
(C) : 4 students
(D) : 1 student
(E) : 19 students

Astronomy current events question: CubeSat ASTERIA test

Astronomy 210L, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Calla Cofield, "Astrophysics CubeSat Demonstrates Big Potential in a Small Package" (April 12, 2018)
jpl.nasa.gov/news/news.php?feature=7097

The Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) satellite recently proved low-cost spacecraft can steadily monitor a star's brightness to search for:
(A) solar flares.
(B) parallax.
(C) repeating nova explosions.
(D) Doppler shifts.
(E) orbiting exoplanets.

Correct answer: (E)

Student responses
Sections 30679, 30680
(A) : 4 students
(B) : 2 students
(C) : 4 students
(D) : 0 students
(E) : 24 students

Astronomy current events question: "Ultima Thule"

Astronomy 210L, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Tricia Talbert, "New Horizons Chooses Nickname for 'Ultimate' Flyby Target" (March 13, 2018)
nasa.gov/feature/new-horizons-chooses-nickname-for-ultimate-flyby-target

NASA's New Horizons spacecraft will visit (486958) 2014 MU₆₉, nicknamed "Ultima Thule," which means:
(A) "Eternal Twilight."
(B) "Final Destination."
(C) "King Thule's Last Voyage."
(D) "Beyond the Northernmost Island."
(E) "Ancient Forest of Darkness."

Correct answer: (B)

Student responses
Sections 30679, 30680
(A) : 4 students
(B) : 7 students
(C) : 3 students
(D) : 20 students
(E) : 0 students

Online reading assignment: radioactive decay modes

Physics 205B, spring semester 2018
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 radioactive decay modes.


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 atomic number represents the total amount of protons. The nucleon number represents the combined number of protons and neutrons. The number of neutrons can be determined by having the nucleon number minus the atomic number."

"The different decays all achieve stability through different means. Some expel particles while other transform particles into other ones."

"The key to stability is being able to keep the protons in the nucleus together. Alpha decay is how a nucleus with excess protons achieves a more stable configuration. Beta-minus decay is how a nucleus with excess neutrons achieves a more stable configuration. Beta-plus decay is how a nucleus that is neutron deficient achieves a more stable configuration. Gamma decay is how a nucleus achieves a more stable configuration, but not because it has too many protons, or the wrong ratio of protons to neutrons."

"For all atomic nuclei the key to stability is being able to keep the protons in the nucleus together. Also, having a certain number of neutrons in the nucleus will decrease the proton-proton repulsion."

"For all atomic nuclei, to have stability they have to keep the protons in the nucleus together, in spite of them all repelling each other. They need to have the proper ratio of neutrons, approximately equal to or slightly greater than the number of protons. More than 83 protons would automatically make the nucleus unstable."

"Stability conditions. A nucleus with more than 83 protons will always be unstable. Neutrons help to balance out proton to proton repulsion so it's necessary to have more neutrons than protons in a nucleus in order to be stabilized. The different decay processes we are learning about are used by nuclei to help them reach stable conditions depending on what makes them unstable to begin with."

"Radioactive decay occurs in four ways. If a nucleus has more than 83 protons, it will emit He to decrease p and n equally (alpha particles). If protons are significantly less than neutrons, neutrons will be converted to protons, releasing antineutrinos and electrons (Β^– particles). If protons are more numerous than neutrons, protons will be converted to neutrons, releasing positrons (Β⁺ particles) and neutrinos. Nuclei become excited after decay and will release photons to 'calm down' (gamma particles)."

"This is pretty basic chemistry stuff, it doesn't seem to be a problem."

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 different types of decay--from a problem-solving perspective it would just be nice to see some different examples going through how to sort each type of decay."

"Most of this was a good refresher on decay and specifically all of the types of it that I learned in the tail-end of my general chemistry series last year."

"I don't understand the difference between a nucleus that is stable or unstable."

"Electron capture and the 'swallowing' thing. And also a bit of gamma decay."

"I like radioactive decay."

"I am having a harder time with gamma (γ) decay. I will do more research to clarify the topic but for right now I'm not grasping it."

"I feel like electron capture was passed over too quickly, I don't really understand what happens."

"What is a neutrino and can it be positive or negative?"

"Outside of confusing the different decay processes this is thankfully review from other classes. "

Explain what a "nucleon number" is, and/or describe how to calculate it for a nucleus.

"It is the total number of protons and neutrons inside the atomic nucleus."

"The nucleon number is the total number of nucleons (protons and electrons), such that the number of neutrons is the difference between the nucleon number and atomic number."

"Not there yet."

Identify the processes that increase, decrease, or do not change the number of protons in the nucleus.
(Only correct responses shown.)

α decay: decrease. [77%]
β– decay: increase. [77%]
β+ decay: decrease. [77%]
electron capture: decrease. [38%]
γ decay: does not change. [69%]

Identify the processes that increase, decrease, or do not change the number of neutrons in the nucleus.
(Only correct responses shown.)

α decay: decrease. [69%]
β– decay: decrease. [65%]
β+ decay: increase. [65%]
electron capture: increase. [19%]
γ decay: does not change. [65%]

Identify the processes that change a proton to a neutron, or change a neutron to a proton in the nucleus.
(Only correct responses shown.)

α decay: no p/n conversion. [62%]
β– decay: n → p. [73%]
β+ decay: p → n. [69%]
electron capture: p → n. [35%]
γ decay: no p/n conversion. [69%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Quiz 6 is going to be awful...I have such a hard time with the right-hand rules and flux laws."

"This seems like it is going to be the most interesting section to date!"

"I think I'll like this chapter a lot better than the previous ones!"

"Could we go over electron capture?"

Online reading assignment: radioactive decay rates

Physics 205B, spring semester 2018
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 radioactive decay rates.


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.

"Exponential and half life decay are both covered well in general chemistry so it's somewhat of a review. But the M&Ms® example is still helpful."

"I understood the introduction to radioactive decay and half-lives. I feel like most of this is from previous biology and chemistry classes."

"Thankfully, this presentation was a bit of a refresher from my other physical science classes. Radioactive dating helps us determine how long the radioactive substance has been around, assuming that there are no daughter atoms to begin with."

"I understand that older substances have more daughter atoms in them. Different elements have different half-lives."

"When there are more daughter atoms the sample is older. The daughter are released when the sample that is being melted, which will then determine the age of the material/sample."

"Radioactive decay can be used to determine the age of an unknown material. This is done using half-lives to measure the time these radioactive materials decay in the unknown material."

"Gaseous daughter atoms can be compared to the amount of radioactive atoms left in a sample to determine how long ago the sample started. After a molten sample solidifies, it will start anew with having radioactive atoms with no daughter atoms."

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 actually feel okay with this stuff thanks to chemistry and other classes I've taken that have dealt with radioactive decay. Going through the slides one more time will help me understand things more."

"There wasn't anything too confusing from the presentation preview. I have learned about radioactive decay in other classes before."

"I don't understand the equation for half-life decay, or radioactive dating."

"I would like to go over problems to get more familiar with the equations."

"I'm confused with the section on radioactive dating, or carbon dating. How exactly is the age of something determined?"

"I don't understand the process to calculate the half life of a material or why melting an object affects its half-life."

"How is the clock reset when matter is solidified after melting if gaseous daughter particles escape?"

"I am struggling with the melting and solidification ages."

"At the moment I am not sure what I find confusing. Most of the lecture made sense to me as far as I am concerned."

State the SI units for activity (radioactive decays per time).

"Decays/s."

"s^–1."

"Bq, or becquerel."

"Curies?"

"Lambda?"

"Not sure."

For a radioactive decay process, the time constant τ ("average lifetime") is __________ half-life T_1/2.

less than.	** [2]
equal to.	***** [6]
greater than.	******************* [19]
(Unsure/guessing/lost/help!)	** [2]

Two samples are each comprised of 800 unstable atoms that will undergo radioactive decay. The remainder of one sample is 200 inert, stable atoms not involved in a radioactive decay process. The remainder of the other sample is 200 daughter atoms of the radioactive decay process.
(Only correct responses shown.)

Sample with more activity (decays/time): (there is a tie). [24%]
Sample with older solidification age: radioactive sample with daughter atoms. [45%]

Describe what changes in a sample when it melted and then solidified that resets its solidification age as determined by radioactive dating.

"Daughter atoms are released and are compared to the radioactive atoms that are left in the sample. Melting it resets its solidification age."

"Since daughter atoms (which are used to date the substance) are gaseous, when the substance is melted they are released. Therefore, they are no longer in the substance effectively resetting the age of the substance."

"There are technically no radioactive atoms or daughter atoms in the sample anymore, so it can reset its solidification age."

"Gaseous daughter atoms are released. This tells us how long ago the sample started with radioactive atoms with no daughter atoms."

"When a substance is liquified the once solidified daughter atoms are released into the air. When the substance is allowed to cool back into a solid the daughter atoms to not solidify back into the original state. This makes its a less reliable in radioactive dating."

"Not sure."

"Hmm..."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I really still think I need help with Lenz's law and Faraday's law."

"The semester after spring break is harder than I thought. But I think I will be able to catch up for the final."

"I need to play Half-Life again."

"I'm excited to eat M&Ms®!!!" (Wait for it--we'll get to do this in the last lab.)

Astronomy current events question: Fast-Evolving Luminous Transient (FELT) explosions

Astronomy 210L, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Ray Villard, Armin Rest, "Kepler Solves Mystery of Fast and Furious Explosions" (March 26, 2018)
http://hubblesite.org/news_release/news/2018-18

NASA's Kepler space telescope's observations of Fast-Evolving Luminous Transient (FELT) explosions may be explained by stars that expel __________ before becoming supernovae.
(A) antimatter.
(B) gas and dust.
(C) dark matter.
(D) neutrinos.
(E) x-ray pulses.

Correct answer: (B)

Student responses
Sections 30679, 30680
(A) : 3 students
(B) : 20 students
(C) : 4 students
(D) : 6 students
(E) : 6 students

Astronomy current events question: volcanic interactions with Mar's oceans?

Astronomy 210L, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Robert Sanders, "Mars' Oceans Formed Early, Possibly Aided by Massive Volcanic Eruptions" (March 20, 2018)
eps.berkeley.edu/news/mars’-oceans-formed-early-possibly-aided-massive-volcanic-eruptions

Researchers propose that Mars' oceans formed much earlier and shallower than previously thought, due to:
(A) volcanic activity.
(B) comet bombardment.
(C) global cooling.
(D) perchlorate rains.
(E) global sandstorms.

Correct answer: (A)

Student responses
Sections 30679, 30680
(A) : 29 students
(B) : 6 students
(C) : 2 students
(D) : 1 student
(E) : 1 student

Astronomy current events question: life in Venus' dark clouds?

Astronomy 210L, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Terry Devitt, "Is There Life Adrift in the Clouds of Venus?" (March 30, 2018)
news.wisc.edu/is-there-life-adrift-in-the-clouds-of-venus/

Researchers propose that dark patches in Venus' atmosphere could be caused by __________ in its clouds.
(A) hydrocarbon hurricanes.
(B) black lightning.
(C) floating microbial life.
(D) sulfuric acid rain.
(E) volcanic outgassing.

Correct answer: (C)

Student responses
Sections 30679, 30680
(A) : 0 students
(B) : 0 students
(C) : 26 students
(D) : 6 students
(E) : 7 students

Astronomy quiz question: star cluster with medium-mass protostars

Astronomy 210 Quiz 6, spring semester 2018
Cuesta College, San Luis Obispo, CA

A star cluster with medium-mass protostars would also have __________ at the same time.
(A) massive main sequence stars.
(B) red dwarfs.
(C) white dwarfs.
(D) giants.

Correct answer (highlight to unhide): (A)

All stars in a star cluster are born at the same time, but undergo stellar evolution at different rates depending on their masses. Medium-mass stars start out as protostars, then reach their main sequence stage, and subsequently become giants, planetary nebulae, and then white dwarfs. So a star cluster with medium-mass protostars cannot have giants nor white dwarfs at the same time, as these are stages that follow the protostar stage of a medium-mass star.

A red dwarf is a low-mass star that has evolved from its protostar stage to its main sequence stage; this takes much longer for a medium-mass star to evolve from its protostar stage to its main sequence lifetime. So a star cluster with medium-mass main sequence stars cannot have red dwarfs at the same time.

A massive star will evolve from its protostar stage to its main sequence stage at a rate much rapidly than medium-mass stars. Thus it is plausible that a star cluster with medium-mass protostars can have massive main sequence stars at the same time.

Section 30676
Exam code: quiz06s0ho
(A) : 17 students
(B) : 5 students
(C) : 10 students
(D) : 10 students

Success level: 44% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.55

Astronomy quiz question: star cluster with medium-mass main sequence stars

Astronomy 210 Quiz 6, spring semester 2018
Cuesta College, San Luis Obispo, CA

A star cluster with medium-mass main sequence stars would also have __________ at the same time.
(A) red dwarfs.
(B) supergiants.
(C) white dwarfs.
(D) giants.

Correct answer (highlight to unhide): (B)

All stars in a star cluster are born at the same time, but undergo stellar evolution at different rates depending on their masses. Medium-mass stars start out as protostars, then reach their main sequence stage, and subsequently become giants, planetary nebulae, and then white dwarfs. So a star cluster with medium-mass main sequence stars cannot have giants nor white dwarfs at the same time, as these are stages that follow the main sequence lifetime of a medium-mass star.

A red dwarf is a low-mass star that has evolved from its protostar stage to its main sequence stage; this takes much longer for a medium-mass star to evolve from its protostar stage to its main sequence lifetime. So a star cluster with medium-mass main sequence stars cannot have red dwarfs at the same time.

A supergiant is a massive star that has evolved from its protostar stage to its main sequence stage, and subsequently used up all of its core hydrogen exit its main sequence stage. Since massive stars evolve much more rapidly than medium-mass stars, then it is plausible that a star cluster with medium-mass main sequence stars can have supergiants at the same time.

Section 30674
Exam code: quiz06nG4s
(A) : 8 students
(B) : 5 students
(C) : 4 students
(D) : 6 students

Success level: 28% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.43

Astronomy quiz archive: stellar evolution

Astronomy 210 Quiz 6, spring semester 2018
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz06nG4s


Section 30674

0- 8.0 :
8.5-16.0 :	**** [low = 11.0]
16.5-24.0 :	***
24.5-32.0 :	******** [mean = 27.3 +/- 8.9]
32.5-40.0 :	******** [high = 40.0]

Section 30676, version 1
Exam code: quiz06s0ho


Section 30676

0- 8.0 :	**** [low = 7.5]
8.5-16.0 :	******
16.5-24.0 :	*********** [mean = 23.8 +/- 9.4]
24.5-32.0 :	***********
32.5-40.0 :	********** [high = 40.0]

Online reading assignment: the Milky Way (SLO campus)

Astronomy 210, spring semester 2018
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 the Milky Way's shape, size and composition and spiral arm structure and formation.


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.

"It's pretty crazy to think we don't know what our galaxy looks like for sure."

"That we are able to observe that our galaxy has a disk shape even though we cannot get a real image of what it is like from an outside point of view."

"The fact that the entire galaxy is not made up of stars. and that the stars we do see is only apart of the milky way galaxy."

"The spiral arms--I think galaxies are so unique and colorful, learning more about the shapes interests me."

"How we are able to perceive our position in the Milk Way by observing star clusters above and below us."

"Dark matter--that we're able to observe galaxies and deduce their gravitational patterns without really understanding where it comes from or being able to quantify those characteristics."

"The description of dark matter was both interesting and confusing, because why does dark matter effect nothing on the outside of the halo? Why does it occur in a perfect sphere if there are multiple sources?"

"The analogy where we looked at dark matter in the terms of a criminal at large. It really makes sense to have its existence put in terms of this situation. I really liked the phrase 'though the case may never be definitively solved, doesn't mean that this person (dark matter) doesn't exist.' Why is this interesting to me personally? I think any time information that is confusing to me can be put into some type of cool analogy I am set."

"Dark matter, despite the fact that we do not know much about it."

"Dark matter is really interesting. I think just for the simple fact that we don't fully understand it, I am intrigued by it."

"Dark matter, because I didn't know it made up the majority of the Milky Way."

"Density waves interest me but also very much confuse me!? I really like the fact it helps make our beautiful galaxy even more so. I also think it's badass that our galaxy gets its spiral arms from swallowing others!"

"Density waves and how they are caused! Gravitational interactions from the collision of thin disk galaxies (with no spiral arms) pulling in dwarf galaxies causing 'ripples' that form density waves."

"I have no doubt that there were many things that would have been interesting."

"All of it."

"All I know is that I want PimpStar Rims on my car. It would be so cool.

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.

"I'm confused about all the information that we can find in the H-R diagram. I can't keep track of it."

"The section on globular clusters and cepheid variables is super-confusing. I don't really understand how those things work at all, honestly."

"Dark matter, because it's cool and strange."

"Dark Matter. How the heck does that stuff work?"

"Dark matter...all I know is that there is not much to learn since not much is known of it in the first place."

"How is the spinning of the Milky Way related to the way light-up rims spin on car tires?"

"How Milky Way spiral arms can grow back such as the legs of sea stars."

"Density waves! What kind of time frame are we talking about with these stars living and dying? How solid is the evidence we have and how can we improve from what we have already? What's the next evolution is solidfying or discovering more solid information about of true shape and size?"

"Nothing."

"I know everything so I'm not confused at all."

"Everything is slightly confusing for me until P-dog breaks it down for us in class."

In your experience, how much of the "Milky Way" (the band of faint stars across the celestial sphere) have you been able to see in the night sky?

As much as can be seen with the naked eye.	*************** [15]
Not very much.	********** [10]
Barely seen it.	****** [6]
(Never been able to see it.)	**** [4]
(Unsure/guessing/lost/help!)	*** [3]

Using the most powerful light-gathering optical telescopes in the darkest skies, __________ of the stars in our entire galaxy can be observed from Earth.

1%.	********** [10]
5%.	**** [4]
10%.	**************** [16]
50%.	* [1]
100%.	[0]
(Unsure/guessing/lost/help!)	******* [7]

If you did not have access to a mirror while camping, what could you do to find out whether or not you're having a bad hair day?

"Find still water."

"I would look at my reflection from a metal spoon."

"A camera! Take a picture and see how it looks!"

"Know that I'm gonna have one regardless."

"Only leave the tent at night so nobody can tell."

"Assume it's bad and put a hat on."

"I'd leave it, lol it's just camping. I don't think the birds, bears, and deer are going to care too much over a few fly away hairs."

"Ask a friend/fellow camper to describe to you the state of your hair to you."

"You could feel with your hands to see if any hair is going in any crazy directions."

"Use my shadow."

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.

"They hook up lights to your rims that light up with your car."

"The images are created using a strobe modulation technique. LED lights are timed to light up at certain points in a full rotation so that, to the naked eye, a still image is created with multiple flashing images."

"As the wheel is spinning the individual lights are programmed to blink at a certain time and gives the viewer an image. If the wheels were not spinning and the lights still blinked the same you wouldn't see an image."

"The lights that flash are timed and synced up to the speed that the wheel goes in order to light up at the correct time making really cool patterns and light combos on the face of the wheel."

"It has to do with lag and certain timing of when lights need to flash or not flash."

"Persistence of vision: flickering lights plus motion/movement."

"Voodoo."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

I liked the spinning light-up rims analogy."

"What do the light-up wheels have to do with us learning about the Milky Way?"

"Do you have PimpStar Rims on your car?" (I have them on my bicycle.)

"Do you think we will ever be able to really understand dark matter? (Probably, hopefully it's a graduate student that makes that discovery, he/she will get full credit and a Nobel Prize.)

"Can you get fired for __________ inside a classroom?" (The first of astronomy class is you do not talk about astronomy class. #siristhisatest)

"I have two exams before tomorrow's quiz, so other than quiz prep, I haven't had much time to focus on the new material. I'll get to read tomorrow!"

Do we (the students) have to always ask a question or make a comment for every weekly survey in order to get credit?" (No, this last section is optional. However, if you leave a lot of the sections above blank, then you can make up for that by leaving something substantial here.)

Is our final cumulative? (Yes, but selectively cumulative, not "everything cumulative." You'll be given a definitive list of things on a study guide, and if something's not on that list, then it's not on the final exam.)

"Hello?" (Yo.)

"No comment." (You just did.)

"I have been watching a lot of slime videos and all of the galaxy pictures look like slime I could make."

Online reading assignment: flux laws & devices

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 presentations on flux laws and devices.


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 am beginning to understand generators better now, and better understand how moving a magnet creates energy than when I did the last reading assignment."

"The magnetic flux Φ_B is the product of the magnetic field magnitude B and the area A. The maximum magnetic flux occurs if the magnetic field is perpendicular to the surface."

"Magnetic flux is an area multiplied by a magnetic field. Faraday's law says that an induced emf occurs in a wire loop when the magnetic flux through it changes."

"Magnetic flux Φ_B is the product of the magnetic field magnitude B and the area A. Units of T·m² or webers."

"Induced current opposes Φ_B change."

"Induced emf, which is produced by changing magnetic flux."

"The slide-rail generator and Faraday's law. The faster the rod moves, the more area there is, thus more emf is produced. In addition, if magnetic flux is constant, an emf can not be produced."

"Faraday's law states that an induced emf in a wire loop occurs while the magnetic flux through it changes. If flux is constant there is no emf. Induced current always opposes the magnetic flux. Differing primary and secondary coil turns allow emf to be stepped up or down."

"How transformers work to step up or down the voltage from the primary loop to the secondary loop."

"I'm not sure I really understand any of this lesson."

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 slide-rail generator--how the force generated on charges through the rod makes the ends charged."

"I'd like clarification on what magnetic flux is, I'm still confused by it after reading the examples."

"How magnetic flux works with the induced current."

"How and when to apply Lenz's law."

"I am confused in the situational uses of these equations. More in-class assistance and instruction would be helpful."

"I found the section on transformers pretty confusing. Also the step-down vs. step-up stuff didn't make a lot of sense to me."

"A little bit of everything is confusing. I just need to make the connections between the different piece...Lenz's law is not yet understood."

"I definitely need a lot of explaining on this stuff I cannot grasp the concepts from just reading the lectures online."

"What is Lenz's law? I don't know what is used for and what context it is useful. Really some explanation for me here would go a long way."

"How to incorporate RHR3 to Lenz's law."

"I'm pretty confused about most of this lesson."

State/describe the symbol used for magnetic flux, and give its SI units.

"Magnetic flux Φ_B is the product of the magnetic field magnitude B and the area A. Units of T·m² or webers."

The symbol looks like a circle with a vertical line through it and it is the product of a magnetic field and an area."

For each situation involving magnetic flux and a wire loop, determine whether or not there would be an induced current in the loop.
(Only correct responses shown.)

Constant zero magnetic flux: no induced current in loop [87%]
Constant non-zero magnetic flux: no induced current in loop. [39%]
Magnetic flux increasing in strength: induced current in loop. [83%]
Magnetic flux decreasing in strength: induced current in loop. [52%]

For an ideal transformer that "steps-down" voltage from its primary coils at 120 V to its secondary coils at 2.1 V, determine what happens to the current and to the power from its primary coils to its secondary coils.
(Only correct responses shown.)

Current: stepped-up (increases). [30%]
Power: no change. [39%]

For an ideal transformer that "steps-up" voltage from its primary coils at 1.5 V to its secondary coils at 220 V, determine what happens to the current and to the power from its primary coils to its secondary coils.
(Only correct responses shown.)

Current: stepped-down (decreases). [30%]
Power: no change. [35%]

Explain why a transformer that has the same number of primary coils and number of secondary coils would not be useful.

"There would be no change in emf as the ratio of N₂ to N₁ would be 1."

"The transformer would not be able to regulate voltage to step it up or down. The primary coil and secondary coil turns cannot be the same amount."

"The whole point is that they have a different number of turns in order for voltages to be stepped up or down."

"Because nothing is being transformed."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Following this pace is getting hard."

"Please go over these examples I am very lost on this subject!"

"Help..."

Online reading assignment: the Milky Way (NC campus)

Astronomy 210, spring semester 2018
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 the Milky Way's shape, size and composition and spiral arm structure and formation.


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 enjoyed learning about the Milky Way. I thought it was interesting to see how large it is compared to everything else, which blows my mind."

"The Milky Way, considering I can see it at my house, so learning about it will be interesting."

"That even though we are in the Milky Way, we can still tell what size and shape it is by using different methods."

"The fog model because it explains why we can only see part of our Milky Way and not the whole thing, and it is one of the easier models to understand."

"That all the stars in our galaxy are actually in their own orbit, they're not static in their position in space. As Earth moves around the sun, the sun is moving in its own orbit around the Milky Way."

"Dark matter."

"The formation theroies, because they started to give me a sort of eye-opening experience as to crazy is was that the Milky Way Galaxy had been created and how everything had fallen into place to create the galaxy, let alone create life on Earth."

"Okay, this is going to sound dumb, but since we have been studying spiral and elliptical galaxies, it just hit me hard that we are in a spiral one. We are in between the Sagittarius and Perseus Arms! Like I knew the Milky Way was spiral, but I now I'm looking at it and it's crazy that life exists in these things."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.

"Without being able to see the entire Milky Way, how are we able to ascertain its shape and look?"

"Globular clusters--it's weird how they can determine how far we are from the center of the Milky Way."

"Dark matter is confusing, because what is it?"

"The density waves were a little confusing for me, and also the radio wave/far-IR maps of the Milky Way."

"I found the spiral arms and spurs to be confusing, what are they made of? Just living and dying stars?"

"How stars form inside of the spiral arms. It says that they form inside gas, but where does the gas come from? Does it come from stars that have died?"

"That spiral arms are just an illusion? Density waves? Why does it have to be like this?"

In your experience, how much of the "Milky Way" (the band of faint stars across the celestial sphere) have you been able to see in the night sky?

As much as can be seen with the naked eye.	*** [3]
Not very much.	******* [7]
Barely seen it.	** [2]
(Never been able to see it.)	***** [5]
(Unsure/guessing/lost/help!)	[0]

Using the most powerful light-gathering optical telescopes in the darkest skies, __________ of the stars in our entire galaxy can be observed from Earth.

1%.	**** [4]
5%.	[0]
10%.	******* [7]
50%.	** [2]
100%.	[0]
(Unsure/guessing/lost/help!)	**** [4]

If you did not have access to a mirror while camping, what could you do to find out whether or not you're having a bad hair day?

"Use my phone camera."

"Use your phone, you don't even have to turn it on--if you get it in the right light you can see your reflection."

"Use the back of a metal spoon or any shiny metal object if you camp that way."

"Fill a pot or bucket with water, set it on the ground and let the water get still, then look!"

"Reflection off a car window."

"Look at the reflection in a river or body of water."

"The facial expressions of the people I am with."

"Ask a fellow camper. Or don't bother, since we are camping, odds are that other campers are having just as much of a bad hair day as me."

"Just touch your hair."

"Look at your shadow to see an outline of your hair to see if its frizzy or not."

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.

"The wheels have built in LEDs that flash or strobe at a certain speed, matching the speed of the wheel, to create the illusion of a still image."

"They are basically led lights hooked up to your rims and use wifi to display whatever image you choose to show while your wheels are spinning."

"A strip of lights cause the illusion of the entire wheel to light up when moving--you know, technology."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I love camping...in a trailer."

"Can we, as a class, go camping for our final and look at the stars all night with telescopes?" (I feel that I can't trust you enough yet to tell me if I were having a bad hair day while camping.)

"Would you ever get PimpStar Rims?" (I already have something like that on my bicycle tires.)

"Will there be any extra credit opportunities for this semester?" (At least one more, next week.)

"Do you like Star Wars?" (#happybeeps)

Physics quiz archive: circuits (2)

Physics 205B Quiz 5, spring semester 2018
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz05z0m6



Sections 30882, 30883 results

0- 6 :
7-12 :	***** [low = 9]
13-18 :	*************** [mean = 18.4 +/- 4.4]
19-24 :	******************* [high = 24]
25-30 :

Online reading assignment: generators

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 presentations on generators.


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.

"A single-pass generator cannot indefinitely continue to slide the rod along the rails to generate a constant motional emf and current."

"More common generators have a coil that rotates between the north pole and south pole of an external magnet. This also generates a motional emf that can be measured with a voltmeter, or made to generate current, but the values of the motional emf (and current) will fluctuate over each cycle of rotation, or even change direction."

"A Faraday disk is an example of a continuous generator, while motional emf are examples of single-pass generators."

"Motional emf is generated when a metal rod is moved through a magnetic field. The way to calculate motional emf is via multiplying the length of the rod by the speed of the rod by the magnetic field through which it is going through."

"Motional emf arises because a magnetic force acts on the charges in a conductor that is moving through a magnetic field."

"Single-pass generators can only be used once before having to be reset. Hoop-drag and rail generators are two types of single-pass generators."

"There are different kinds of generators. Some need to be reset (single-pass) before they can be used again, while some generators are continuous and can keep providing current and emf."

"There are many different types of generators that work in different ways. We are still using the right-hand rules for these generators."

"Single-pass generators can only be used once before having to reset them. In a uniform magnetic B field, electrons in a metal rod experience a downwards pointing force, and as long as the rod is made to move through the field, its bottom will be negative and the top positive. Therefore, moving this rod in a B field makes it a battery. Continuous generators do not need to be reset to provide emf and current. An example of this is a Faraday disk, where the north and south pole lie between the external magnet. All you do is crank it to generate emf. Rotating coils are also commonly used."

"How to use the right-hand rule when applying it to generators and all kinds of magnetic fields."

"Learned more on how to use my hands to solve problems."

"I understand that I don't know how generators work."

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 would like to learn more on the motional emf."

"How to determine the direction of magnetic force for a rod that is being rotated from one end."

"Still not really intuitively understanding how generators work and what the 'resetting' is about. I get the idea of having to 'move the snowboard back up the rail,' but I don't really understand what is meant by resetting in a generator, especially for the rotating rod (Faraday disk)."

"More explanation on how to use the right-hand rules for the generators would be helpful."

"It is hard for me to use the right-hand rule to determine where the forces are going with a rod moving through magnetic fields for single-pass generator diagrams."

"The motional emf animation, and how the variables relate as well as the units."

A metal rod moves to the right along a magnetic field that points into the page. The direction of the magnetic force on (fictitious) positive charges in the rod is:

up ↑.	*************** [15]
down ↓.	******** [8]
left ←.	*** [3]
right →.	* [1]
into the page ⊗.	[0]
out of the page ⊙.	*** [3]
(No direction, as this quantity is zero.)	[0]
(Unsure/guessing/lost/help!)	** [2]

A metal rod pivoted at one end rotates counterclockwise in a magnetic field that points out of the page. The direction of the magnetic force on (fictitious) positive charges in the rod is:

in towards the center of rotation.	***** [5]
out away from the center of rotation	******************* [19]
into the page ⊗.	*** [3]
out of the page ⊙.	** [2]
(No direction, as this quantity is zero.)	[0]
(Unsure/guessing/lost/help!)	*** [3]

Explain what a generator is supposed to "generate."

"Generators generate a motional emf."

"Emf and current."

"Generates a current and motional emf, eventually creating power."

"Electric potential energy."

"Electricity?"

Explain the meaning of "motional" in the term "motional emf."

"That the emf is created through motion."

"Energy is created via movement of a metal rod through a magnetic field."

"It means something is constantly moving to produce the emf."

"The motion of the bar is what creates the emf, thus 'motional emf.'"

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"This is all becoming pretty foreign to me, any worksheets and practice in class will definitely benefit me!"

"what are the benefits of making a single-pass generator over a continuous generator?" (Single-pass generators are not very practical (as you must stop producing electricity in order to "reset" the system), but are much easier to understand conceptually. More practical, continuous generators (that don't have to, or automatically "reset" by returning to their starting point) are a bit more difficult to understand.)

"Aren't you still technically putting in some energy for the system to reset a continuous generator, just as in the single-pass generator?" (You actually put energy into all generators (they just convert your kinetic energy into electric potential energy), but you wouldn't have an abrupt break trying to reset a continuous generator (and can generate electricity uninterrupted), compared to a single-pass generator like a slide-rail generator, where you would have to pick up the rod at the end of a (finite) set of rails, pick it up to put it back to the beginning (or you would need to stop the rod, and start sliding it backwards along the rails.)

"I'm excited that we are learning useful stuff for the zombie apocalypse." (I'm excited, too.)