20180517

Astronomy final exam question: comparing temperatures and sizes of main-sequence stars

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

An astronomy question on an online discussion board[*] was asked and answered:
Srr: Is it possible for two main-sequence stars to have different temperatures and different sizes but the same luminosity?
Rgr: No, because more massive main-sequence stars are hotter and larger than the lesser massive main-sequence stars, they cannot have the same luminosity.
Discuss why this answer is correct for main-sequence stars, and how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.

[*] answers.yahoo.com/question/index?qid=20110511035317AAeHphE.

Solution and grading rubric:
  • p:
    Correct. Discusses how the Stefan-Boltzmann law and/or H-R diagram shows that along the main-sequence, the more-massive stars will be located in the hotter, larger, brighter upper left-hand corner, while the less-massive stars will be located in the cooler, smaller, dimmer lower right-hand corner, so they cannot have the same luminosity.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. May have compared two stars in general, rather than explicitly comparing two stars on the main-sequence line.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30676
Exam code: finalSuB1
p: 24 students
r: 7 students
t: 4 students
v: 1 student
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 0707):

Another sample "p" response (from student 0219):

Astronomy final exam question: comparing temperatures and luminosities of main-sequence stars

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

An astronomy question on an online discussion board[*] was asked and answered:
NiH: Can a large size main-sequence star have a hotter temperature and brighter luminosity than a smaller size main-sequence star?
Bes: Yes, it could be possible that a large size main-sequence star can have a hotter temperature and brighter luminosity in comparison to a smaller size main-sequence star that has a cooler temperature and dimmer luminosity.
Discuss why this answer is correct for main-sequence stars, and how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.

[*] answers.yahoo.com/question/index?qid=20101127053013AACmzKM.

Solution and grading rubric:
  • p:
    Correct. Discusses how the Stefan-Boltzmann law and/or H-R diagram shows that along the main-sequence, the larger stars will be located in the hotter, brighter upper left-hand corner, while the smaller stars will be located in the cooler, dimmer lower right-hand corner.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. May have compared two stars in general, rather than explicitly comparing two stars on the main-sequence line.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30674
Exam code: finaln3sT
p: 9 students
r: 9 students
t: 1 student
v: 0 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 2123):

Astronomy final exam question: type II supernovae in star cluster with white dwarfs?

Astronomy 210 Final Exam, spring semester 2017
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:
Pdg: Can there be type II supernovae explosions seen in a star cluster that also has white dwarfs at the same time? Would it have to be a really old or young star cluster?
spota: Yes, if the star cluster is old enough to contain white dwarf stars it will still be young enough to have hydrogen-burning massive stars that can undergo type II supernova explosions.
Discuss why this answer is incorrect, and how you know this. Explain using the properties of mass and stellar lifetimes, evolution of stars, and star cluster ages.

[*] answers.yahoo.com/question/index?qid=20171117015031AAqCPQo.

Solution and grading rubric:
  • p:
    Correct. Understands that star cluster cannot have type II supernovae explosions at the same time as having white dwarfs:
    1. medium-mass stars become white dwarfs well after the end of their main-sequence lifetimes (approximately 10 billion years); and
    2. massive stars will explode as type II supernovae after the end of their main-sequence lifetimes (less than a million years); such that
    3. a star cluster with white dwarfs, will not have any supergiants remaining that can explode as type II supernovae; or a star cluster with supergiants exploding as type II supernovae will have medium-mass stars that have not yet reached the end of their main-sequence lifetimes.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Garbled discussion of properties and evolution of stars. May discuss type Ia supernovae or lookback time.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution of stars.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30674
Exam code: finaln3sT
p: 6 students
r: 3 students
t: 5 students
v: 4 students
x: 1 student
y: 0 students
z: 1 student

Section 30676
Exam code: finalSuB1
p: 13 students
r: 6 students
t: 6 students
v: 6 students
x: 3 student
y: 1 student
z: 1 student

A sample "p" response (from student 1777):

A sample "p" response (from student 1217), discussing the house party model of determining star cluster ages:

A sample "y" response (from student 7237):

Astronomy final exam question: metals breaking down in stars?

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

An astronomy question on an online discussion board[*] was asked and answered:
Alexis: Why are metals more abundant in newer stars than older stars?
tdloo: Because the metals haven't had time to break apart yet in newer stars.
Discuss why this answer is incorrect, and how you know this. Explain using the properties of mass and stellar lifetimes, and evolution of stars.

[*] answers.yahoo.com/question/index?qid=20130409190107AA1Ej3v.

Solution and grading rubric:
  • p:
    Correct. Discusses why the answer is incorrect by discussing at least one of the following arguments:
    1. metals are produced in the cores of massive stars (and medium-mass supergiants) by fusion, which entails the combination of atoms, rather than in breaking them apart; or that
    2. metals are typically produced in the cores of previous generation ("old") massive stars, which explode as type II supernovae to scatter these metals that get incorporated into the next generation of "new" stars, such that metals are more abundant in newer stars than older stars.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Garbled discussion of properties and evolution of stars, such as breaking down of metals; masses and evolution rates.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution of stars.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Section 30674
Exam code: finaln3sT
p: 16 students
r: 0 students
t: 1 student
v: 1 student
x: 1 student
y: 0 students
z: 1 student

Section 30676
Exam code: finalSuB1
p: 19 students
r: 1 student
t: 2 students
v: 12 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 5069):

20180516

Online reading assignment question: advice to future students

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. The following question was asked after the last lecture, but prior to the final exam.

Tell a student who is about to take this course next semester what he/she needs to know or to do in order to succeed in this course. (Graded for completion.)
"Do your readings and show up everyday to class because it helps so much more than thinking you can just read the book and be good."

"Show up to class and study for every quiz, it takes a lot of the stress out of the class and makes it very enjoyable."

"Be curious and ask questions."

"Don't forget that the quizzes are due before each class at midnight! And if you're taking astronomy lab, too, it's easy to forget about those assignments as well."

"Make sure you use the starwheel the right way, read the chapters, study your notes and do EVERY online reading asssignment."

"ASK QUESTIONS AND PUT IN EFFORT! This class is so engaging. You'll learn so much. Do your homework, and come to class. It is all worth it. If you put the effort in you will pass this class easily. P-dog is the best."

"Study StUdY STUDY! Get a group of people from your class and study for all quizzes/exams/midterms, anything! It will help you out a lot and don't slack off."

"Always do the homework assignments, they are super-easy and pay attention in class. This is a great course and you will have a lot of fun."

"In order to succeed in this course you need to do the readings, and the homework is important and reviewing the presentations."

"DO THE READING ASSIGNMENTS. ATTEND EVERY LECTURE. BE AMAZED BY SPACE."

"In order to succeed in this class I urge everyone to look at the quiz study guides and make sure to do the online reading assignments."

"Don't procrastinate, go to class, and do the readings! They help immensely with following along in class."

"In order to succeed, I would recommend that you go to all the class sessions, do not forget a single online reading assignment, do all of the extra credit, and try your best not to procrastinate!"

"Preview then presentation slides online so you can be the more confident while being in class or with in-class activities."

"Read the chapter before class and keep your quizzes."

"If one is going to be enrolled in astronomy with Dr. Len, the most important thing to know in order to succeed is to follow @Patrick_M_Len on Twitter. He also posts everything on blogs, from former test questions with correct answers, along with the reading assignments and basically everything related to the course. And being aware of the blogs and what is posted there might help. Former midterm questions are good study guides and Dr. Len shows examples of students answers and grading rubric really shows how he grades and what he looks for."

"Please please PLEASE do the reading assignments and come to class."

"They need to be able to show up to class to get the points that are handed out. It really isn't that hard yet to just do the work that is asked of you."

"Study and listen during lectures."

"Do the homework."

"Read, read, read, and study...by reading."

"Don't get behind on the reading and ask a lot of questions."

"Keep up with reading, get as many points as possible."

"Come to class, do your reading, study for quizzes!"

"Take lots and lots of notes and seriously read the book. Plus make sure you draw the drawings P-dog does in class, they help."

20180509

Astronomy quiz question: spiral arm composition

Astronomy 210 Quiz 7, spring semester 2018
Cuesta College, San Luis Obispo, CA

The spiral arms of a galaxy are primarily composed of:
(A) dark matter.
(B) massive stars.
(C) globular clusters.
(D) type Ia and type II supernovae.

Correct answer (highlight to unhide): (B)

Massive main-sequence stars, which are the brightest and shortest-lived stars, form and die within a short time, essentially traveling the width of a spiral arm. Dark matter and globular clusters are mainly found in the halo of a galaxy, above and below the disk.

Section 30674
Exam code: quiz07nen4
(A) : 2 students
(B) : 8 students
(C) : 9 students
(D) : 2 students
(No responses: 1 student)

Success level: 41% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.86

Section 30676
Exam code: quiz07SumM
(A) : 3 students
(B) : 16 students
(C) : 17 students
(D) : 2 students

Success level: 46% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.48

Astronomy quiz question: red dwarf metallicity

Astronomy 210 Quiz 7, spring semester 2018
Cuesta College, San Luis Obispo, CA

The amount of metals in the outer layers of metal-poor red dwarf will __________ over time.
(A) increase.
(B) remain constant.
(C) decrease.
(D) (A red dwarf cannot be metal-poor.)

Correct answer (highlight to unhide): (B)

Medium-mass and massive stars produce metals (elements heavier than hydrogen and helium) in their cores during their giant/supergiant phases, up through type Ia/II supernovae explosions. Along with their unused hydrogen, these metals are then scattered into the interstellar medium, which are then incorporated into later generations of stars. However, a red dwarf (low-mass star) will only be able to fuse hydrogen to helium, and does not produce more metals.

Section 30674
Exam code: quiz07nen4
(A) : 8 students
(B) : 10 students
(C) : 3 students
(D) : 1 student

Success level: 49% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.38

Section 30676
Exam code: quiz07SumM
(A) : 14 students
(B) : 9 students
(C) : 12 students
(D) : 3 students

Success level: 27% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33

Astronomy quiz archive: Milky Way, nucleosynthesis, cosmology

Astronomy 210 Quiz 7, spring semester 2018
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz07nen4


Section 30674
0- 8.0 :  
8.5-16.0 :   ******** [low = 9.5]
16.5-24.0 :   **** [mean = 22.5 +/- 9.1]
24.5-32.0 :   *******
32.5-40.0 :   *** [high = 40.0]


Section 30676, version 1
Exam code: quiz07SumM


Section 30676
0- 8.0 :   ** [low = 7.5]
8.5-16.0 :   ***********
16.5-24.0 :   ************ [mean = 21.5 +/- 8.0]
24.5-32.0 :   ********
32.5-40.0 :   ***** [high = 40.0]

Online reading assignment: origin of life, are we alone? (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 origin of life, a "Here Is Today" timeline, LEGO® washing tips and the extraterrestrial hypothesis.

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.
"The age of this world; I think that it's interesting Earth has been through many stages."

"That chemical evolution is not considered being alive even though it should be. It is creating something or changing something which makes it seem alive."

"Your pictures are cool because it helps me to visualize what we are learning about and I like that."

"The timeline of Earth, and when life starting appearing, because it is really mind-blowing to see it on a timeline."

"Learning about carbon molecule chains was really interesting. The fact that all the information needed to survive and reproduce is stored on those simple chains is sort of mind-boggling."

"Possible life on other planets because I believe it's kinda scary."

"Origin of life on Earth. Its interesting because it has brought much debate from the science and religious societies."

"The definition of life is interesting. Thinking about life in the way that it does versus what it is."

"I find the history of life on Earth very interesting and the fact that we are such a small part of our history as a planet, yet we will probably be the ones to destroy it, very sad."

"I'm super-interested in the idea of intelligent life throughout our universe, such as traveling between the stars, it's crazy that the fastest human device launched will take about 90,000 years to travel to the nearest star."

"There is an equation for finding the number of communicative civilizations in our galaxy."

"I really enjoyed learning about the Drake equation because though there is no way of using it currently, it is interesting to hear that there is an active search of other advanced life and that it is thought of as a serious possibility."

"I definitely thought that the Drake equation was very interesting. I did not know that it was possible to even form such an equation, yet here it is! I love it."

"I've always found extraterrestrial life interesting and think that it would completely change our lives and culture if we actually were able to converse or communicate with what's out there."

"That this is our last lecture."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I don't understand the timeline you inserted. Like why? What does it mean?"

"I didn't really understand the process in which Julia Child went through to describe the how life on Earth begun."

"I am so CONFUSED of how we haven't been around for that long."

"Traveling between stars because of how long it seems to take to get to each one."

"Carbon molecule chains. 'In order to do things that livings things do, and more importantly, to make sure that a future generation is able to continue doing these things requires a lot of instructions to be stored.' MIND BLOWN."

"I was confused on the chemical evolution portion of this assignment. I thought it was really hard to grasp the idea of things naturally joining together in the fact of adapting to certain area's around Earth. Thus, evolution."

"How the chemistry works with molecules, this is confusing because I need it to be explained since for me chemistry is hard."

"The Drake equation was really confusing for me. I don't know how exactly all those variables are expressed or how they constrain the probability of life in a real sense."

"As usual, the thing I find the most interesting is the same thing that confuses me the most. I do not know what makes up the Drake equation, or how someone even came up with it."

"Everything confused me."

"Nothing really."

Briefly describe a difference between life and non-living things.
"Living things breathe and can reproduce, while non-living things cannot."

"Living things are organisms that are made up of atoms and cells that allow life to move and talk and feel. Inanimate and non-living objects cannot do this."

"A living thing has to be able to adapt in the environment but dose not have to if it is non-living."

"Living things can adapt themselves and their surroundings to accommodate survival, non-living things may last for centuries, but could eventually fade away."

"Life is the ability for cells to grow, develop, manipulate its environment, and have future generations while non-living things have no live cells."

"Living things can evolve and adapt whereas non-living things cannot. One way to tell whether or not something is non-living is to play the song 'Hey Ya!' by OutKast. If the thing does not dance or sing along to the song, it is non-living."

"Living things are alive, non-living things are not."

Rank the time it takes for each of the following to have occurred on Earth.
(Only correct responses shown.)
Time after the formation of Earth for single-cell life to arise: about 1 billion years [13%]
Time for the first types of simple single-cell life to evolve into fishlike creatures: about 3 billion years [4%]
Time for fishlike creatures to evolve into more complex land-based animals today: about 0.5 billion years [38%]

How important is it to you to know whether or not there may be life elsewhere other than on Earth?
Unimportant.  * [1]
Of little importance.  **** [4]
Somewhat important.  **** [4]
Important.  ****** [6]
Very important.  ********* [9]

Briefly explain your answer regarding the importance of knowing whether there may be life elsewhere other than on Earth.
"I feel like Earth is the only place where people can actually survive. It would interesting to know what new discoveries scientists would make but it's not like it would benefit me in anyway. You know what I mean."

"I just want to verify that there are other living organisms in the universe, even if this is as simple as a single-celled organism. Only because that organism can evolve just like we did."

"Because it'd be cool to know of other life forms and see how they live and see if their lifestyle is better than ours."

"Life elsewhere scares me. You don't know if they're gonna be friendly or not."

"I think that there's no way that we are the only living things in this universe, or anywhere other than Earth. It's interesting to think about what it may be, it's (probably) not little green aliens in a flying saucer, but who knows?"

"I think it is important because I don't think that we are alone. Knowing if there is life on other planets could help us answer a lot of questions that we have about our galaxy and may help us with things we are trying to research and fix."

"Other life forms could possibly inform us about how our universe was created, or how life itself has turned into what we know today. finding other organisms would be a huge development in human existence."

"Knowing that there is life elsewhere doesn't change my daily life here."

"I struggled between selecting 'somewhat important' and 'important.' I think that life elsewhere could potentially help but I'm not sure to what extent."

"We are wired for discovery and the fascination of being able to prove life elsewhere is something humans will strive to learn."

"My own personal reason would be existence and the meaning of it. I sometimes go down the rabbit hole of intense thought surrounding this. If we found out that there was life elsewhere I believe it would provide some comfort to me knowing that we aren't in this alone. Not necessarily that there's a purpose to all this but it might create more meaning to our own existence."

"There is no way that we are the only living beings in the universe. I want to know what else is out there."

"It would be very important to know if there was life on other planets or further in the universe. This mostly is because of the natural feeling we get as humans wanting to know more and more in life and where people and living being exist at."

"I love aliens, I love X-Files, and everyone needs to know that life beyond Earth life is important and cool and amazing. The truth is out there."

Which type of star would be least likely to have a planet that could support life?
Although not totally unimportant, right now it does not affect the way I live.
Massive.  ******** [8]
Medium-mass.  ****** [6]
Low-mass (red dwarf).  ***** [5]
(Unsure/guessing/lost/help!)  ****** [6]

Briefly explain your answer to the previous question (type of star least likely to have a planet that could support life).
"Massive stars, because they have a very short life span so they wouldn't be very likely for life to exist on a planet around them."

"It would take about a billion years or so for life to develop elsewhere and massive star wouldn't live that long."

"Because a massive star dies too quickly."

"Massive stars would have the lowest chance of hosting life because they would offer the shortest window of time for life to form because of its shorter main sequence lifetime."

"A low mass star would more than likely not be able to generate enough heat to create life on a terrestrial planet."

"Medium-mass stars would most likely have a planet with complex lifeforms because they wouldn't die as quickly as massive stars, and not be as dim as low-mass stars."

"I don't think any of the stars would have life."

"Wouldn't all of them be unable to have complex forms of life? Since that would be my answer, and it is not even an option, I am wrong and confused lol."

"I guessed."

Describe what the Drake equation is used for.
"A serious look at the possibility of life elsewhere in the Milky Way."

"It is a equation used to figure out now many extraterrestrial intelligent civilizations are out there that we can communicate with in the Milky Way."

"I have no idea."

In your opinion, how plausible is it that the Chilbolton message is a reply from extraterrestrials?
Implausible.  *** [3]
Not very plausible.  ************ [12]
Somewhat plausible.  ****** [6]
Very plausible.  * [1]
(Unsure/guessing/lost/help!)  ** [2]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Do you believe in extraterrestrial life?" (Eh, maybe. We won't really know unless we keeping looking, though.)

"How long do you think it will take most people to do the final exam? (About the same amount of time as a midterm, anywhere from 15-80 minutes, although you are allotted 120 minutes to take the final.)

"Do you think it's plausible that the Chilbolton message is a reply?" (Yes, it's a reply from the radio astronomers who work next door to that field. #mischiefmanaged)

"I'm really enjoying this class." (Now that it's nearly over?)

Physics quiz archive: radioactive decay, Feynman diagrams

Physics 205B Quiz 7, spring semester 2018
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz07N4ci



Sections 30882, 30883 results
0- 6 :   ***** [low = 3]
7-12 :   ******
13-18 :   ******** [mean = 16.2 +/- 7.7]
19-24 :   ********
25-30 :   **** [high = 30]

Online reading assignment question: advice to future students

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. The following question was asked after the last lecture, but prior to the final exam.

Tell a student who is about to take this course next year what he/she needs to know or to do in order to succeed in this course. (Graded for completion.)
"Don't miss a class."

"Don't do the homework at the last minute, and try to understand the material before coming to class. Do the problems and take good notes."

"Honestly, to succeed in this course you need to participate. Come to class, learn as much as you can and don't worry so much about how you're doing in the class or what your exact grade is."

"P-dog's class is helpful in that way because you have enough cushion to where you can actually try to learn the material and you can fail a quiz or two and learn from your mistakes for the midterm. Also, go to office hours if you don't get it, P-dog is pretty chill and no one is ever in there so you can just bombard him with physics questions and he'll show you how to start a fire with steel wool and a battery."

"To succeed in this course, make sure you read, attend all of classes, and make sure your schedule is not too busy."

"It is a good idea to stay on top of the homework and be sure to show up to class! They are very very helpful when it comes to anything that didn't make sense in the homework. Take both semesters with P-Dog! You won't regret it. He is awesome and truly wants you do to well and succeed in all ways possible!"

"The practice problems and homework problems are the best way to learn the material."

"If you read the presentations carefully before class, you will come in to the lecture with a fairly solid understanding of the concepts that are going to be presented. Anything that is not clear in the presentations should be able to be cleared up by the textbook, which is a great supplemental resource."

"I found that going to the class tutor weekly really helped me! "

"I would say you need to be pretty comfortable and disciplined enough to learn the material on your own through the online presentations. I know for myself personally reading something on my own isn't the best way that I learn. I'm more of a student that benefits from professors explaining the topic and going through practice problems. But it is nice to have the material ahead of lecture to prepare yourself for in-class working time."

"Do all the homework and attend all class sessions and you should have a good start! "

"You have to keep up with learning the equations and going over the in-class notes. It's really easy to get lost, especially since we have online presentations. Don't be afraid to bother the embedded tutor during their hours if you have questions!"

"Make sure to do all of the homework and keep up with all the pre-/post-labs. Do the practice problems that are posted before the quizzes and exams. "

"As long as you make sure to study for the two midterms and do (most) of the homework there is no reason you shouldn't get an 'A' in this class."

"Be consistent and diligent with the homework, and GO TO CLASS. Take as many notes as you can and review them. P-dog draws a lot of cartoons that make the material a lot easier to understand."

"Creating my own notes prior to each lecture made everything much more helpful. In the lecture, you will go over problems and you can add these to your notes. Prior to every test, remake those notes with your more current knowledge on the subject and cues that P-dog likes to see in sample student answers. Reviewing the problems he puts on the blogs is extremely important. Not only do you see REAL exam and quiz questions, but you will also see past student answers, their grades, and a description of what each answer needed to be correct. P-daawwwwg can teach this stuff to a third-grader so don't be afraid to ask plenty of questions in class!"

"Study the problems given in homework and class examples."

"Do the homework and post-/pre-labs and everything should be fine."

"Read the presentations before going to class! Even if it is super-confusing, it will be less confusing in class."

"Do all the reading assignments and homework. Don't procrastinate. Ask questions!"

"Take your time when studying the material before lecture if you can. It helps! If you still feel uncertain about things: doing the practice problems provided and making sure you include all the information required makes a huge difference."

"Make sure you don't miss any lectures, that's where I got most of my clarification on confusing topics and where I learned how to complete midterm problems. If you understand the concepts the rest isn't too bad."

"I think it depends of study style but for someone with a slow pace and/or with a different native language; read the blog and take notes, do all the exercises from the course website, take the worksheets seriously, ask the questions that you have to the professor and/or the tutor."

20180508

Online reading assignment: origin of life, are we alone? (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 origin of life, a "Here Is Today" timeline, LEGO® washing tips and the extraterrestrial hypothesis.


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 liked the LEGO®-washing link. I thought it was an interesting way to describe how molecules can form just by being around each other in the right conditions."

"The 'Here is Today' timeline was supercool and interesting to learn a bit about, though still a little confusing."

"Being able to actually see the 'Here is Today' timeline for the things that have taken place to create and maintain life on this planet, and looking just how long from the creation of the planet it took to develop humans."

"The Drake equation, and how it could predict how much life is out in the universe."

"The pessimistic view on the Drake equation because I believe there has to be life out there somewhere in our galaxy. I didn't clearly understand every part of the equation, but from what I deciphered, there has to be life."

"Nothing interested me."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"The Drake equation is a little confusing for me because it’s just hard to put everything together in my opinion and know every detail of it."

"The Drake equation, because how is that a provable equation, even just using statistics? Our sample population of just us is incredibly small."

"The chemistry stuff was confusing because I hate chemistry."

"The crop circles because I don't believe there are aliens doing that. But, they are so well drawn and made for no one to notice doesn't make much sense."

"I was hella confused about everything!"

Briefly describe a difference between life and non-living things.
"We can act on our own with our own thoughts."

"A difference between living and non-living things is the idea that one takes an environment to live within and adapts to the environment to live within."

"Living things are alive and need certain resources (like energy) to stay alive. Non-living things don't, and are dead without needing much."

"Livings things grow and change. Non-living things stay the same or deteriorate over time."

"Living things can reproduce."

"Life is a living thing that should manipulate its environment, adapt to its environment, and store information/instructions (encode). Non-living things would do anything else not listed above."

"One difference is reproduction, where something that is alive is able to reproduce and pass along its genetic material while a non-living thing cannot."

"Life is long chain of molecules, while anything below that, such as a single molecule of molecular chemistry, is not considered life. Life can also be defined as one cell."

Rank the time it takes for each of the following to have occurred on Earth.
(Only correct responses shown.)
Time after the formation of Earth for single-cell life to arise: about 1 billion years [31%]
Time for the first types of simple single-cell life to evolve into fishlike creatures: about 3 billion years [39%]
Time for fishlike creatures to evolve into more complex land-based animals today: about 0.5 billion years [46%]

How important is it to you to know whether or not there may be life elsewhere other than on Earth?
Unimportant.  [0]
Of little importance.  * [1]
Somewhat important.  **** [4]
Important.  ***** [5]
Very important.  *** [3]

Briefly explain your answer regarding the importance of knowing whether there may be life elsewhere other than on Earth.
"That way we can live on a new Earth since ours is most likely going to hell."

"I think it's important to know if life can be possible somewhere else because we surely are killing this planet."

"Earth will eventually die so we need to find a new place to live for future generations long into the future."

"Because if we are alone in the entire universe, that would be truly frightening knowing that we could be the last of life."

"The importance in being able in understanding there there may be life elsewhere opens up so many more ideas about how life is created and can give Earth a better idea on how the universe works or how to sustain the planet better."

"I need to know if there's aliens, are there other lifeforms studying in our galaxy or another galaxy wondering if we exist?"

"It's important for us to know what else is out there and learn about other living things that we are not familiar with. Life is life, and we should know or want to know about other living things."

"I feel like it is important because You would want to know if there is something you are missing or something that may potentially kill you in the future. Its kind of like a scary horror movie."

"It would give a lot of information about the start of life. It would allow us to further explore conditions required for life to start, and how probable it is for it occur in different conditions."

"I would like to know because it could answer more questions about the universe and the other life's take on religion and how it all came to be. Also I love Star Wars and the thought of technologically advanced societies."

"I would like tangible proof that life does exist out there in my lifetime."

"I think it would be really fascinating to find out but it isn't like my life depends on it. "

Which type of star would be least likely to have a planet that could support life?
Massive.  *********** [11]
Medium-mass.  [0]
Low-mass (red dwarf).  * [1]
(Unsure/guessing/lost/help!)  * [1]

Briefly explain your answer to the previous question (type of star least likely to have a planet that could support life).
"It would take a long time to create life in a planet, so the bigger the star, the shorter the lifetime, giving the planet less time to form life within that solar system or planet."

"It took life a long time to form on Earth and since a massive star has the shortest life time, life might not have enough time to form."

"Based on life on Earth, a massive star would be too short-lived for life to form on a planet."

"I don't know."

Describe what the Drake equation is used for.
"The Drake equation multiplies a number of factors that reflect more and more restrictive conditions for an advanced technological civilization to arise to calculate the number of these civilizations just in our galaxy, the Milky Way."

"I dunno."

In your opinion, how plausible is it that the Chilbolton message is a reply from extraterrestrials?
Implausible.  ** [2]
Not very plausible.  ****** [6]
Somewhat plausible.  ** [2]
Very plausible.  * [1]
(Unsure/guessing/lost/help!)  ** [2]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I really liked how you posted the 'Here is Today' timeline on just how long it took to actually create life on Earth from the time it was created and how long it took to create the human race in regards to how long we have had life on this planet. It really helped to be able to put a lot of the ideas into action."

"Do you believe in aliens? (The weird green big-headed things.)" (Nah, not so much. I don't think we're going to be able to even imagine what an alien life form might look like, much less one that somewhat resembles us.)

"So like you explained last class--our final will be optional in the sense that whatever grade we have without taking the final, it will stay as is? It won't bring my grade down right? It will stay the same if I don't take it?" (Yes, yes, and yes.)

"Living things can take in oxygen and breathe, like plants and humans. A pillow can't breathe because it's not alive." (A pillow can also be used to make you not alive.)

"What will you be doing this summer?" (I always wanted to travel to here, but this summer Mrs. P-dog wants to go on a road trip to here instead, and that's okay with me if we get to visit here, here, here, and here on the way there.)

20180507

Online reading assignment: QED, strong, weak interactions

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 Feynman family poses by the famous camper"
Ralph Leighton
symmetrymagazine.org/article/may-2014/saving-the-feynman-van

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.
"We use lines and intersections to draw diagrams that represent particle interactions."

"I am beginning to better understand Feynman diagrams. I understand how time goes and what line is what."

"The decay processes are specific to what each electron is doing. They can all interact with each other in different ways with each process."

"A positively charged proton exchanges photons with a negatively charged electron, producing the Coulomb force of electrostatic attraction. The strong force holds the nucleus together."

"Feynman diagrams are drawings that depict the interactions of electrically charged particles and the virtual proton or photon particles that can be generated. In addition, all of these diagrams must have a particle moving in, a particle being moved out, and a photon being generated or else the electrical particle interaction is not possible."

"If energy is borrow a little amount will last a long time, but a large amount will last a short period of time. As well as the concept of photons, particles, and anti particles."

"In quantum mechanics, forces are attracted by exchanging virtual particles. Virtual means they are measurable by momentum, not mass. The force carriers for nuclear forces are pions. Protons and neutrons are baryons, a type of hadron. Pions are bosons with zero spin."

"I spent most of today reading my chemistry book for a quiz that thankfully is covering the different decay types and electron capture."

"I am really understanding Feynman diagrams. They are quite interesting now."

"The drawing of Feynman diagrams is making more sense now."

"I understand how to draw the diagrams but knowing exactly what they mean is still a little confusing."

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 reading was pretty heavy material. I anticipate lecture informing us on what we need to know."

"More time spent will clear up a lot of things I think, but right now I am very confused about all the different types of interactions and am looking forward to hearing about them in lecture."

"I'm not sure why we have to use Feynman diagrams to describe these sub-atomic reactions, why not write them out as a chemical reaction like the nuclear decay processes?"

"How to tell if something is positively or negatively charged on a Feynman diagram."

"I think I'm alright for now."

"Still confused with the Feynman diagrams, some of the Greek letters confuse me."

"Just need a general overview in class, this material is a lot and a bit dense for sure."

"I am confused when I try to interpret the diagrams. I understand the ABC (always balance charges) and CBA (cancellation by annihilation) rules along with the validity of each (1 line in/out, 1 squiggly). I do not understand how to interpret the diagram themselves. I do also understand that time moves left-to-right. Everything, so sorry."

The above (valid) Feynman diagram depicts an electron exerting a (repulsive) electric force on another electron. The charge of the "virtual" photon (γ) exchanged between them is:
negative.  **** [4]
zero.  ********* [9]
positive.  ******** [8]
(Unsure/guessing/lost/help!)  *** [3]

The above (valid) Feynman diagram depicts two nucleons exerting (attractive) forces on each other. The charge of the pion (π) exchanged between them is:
negative.  ******** [8]
zero.  *** [3]
positive.  ********** [10]
(Unsure/guessing/lost/help!)  *** [3]

The above (valid) Feynman diagram depicts weak force interaction between a proton and a electron. The charge of the "intermediate vector boson" (W) exchanged between them is:
negative.  ** [2]
zero.  ********** [10]
positive.  ******* [7]
(Unsure/guessing/lost/help!)  ***** [5]

The (valid) Feynman diagram in the previous question above depicts a(n) __________ decay process.
α.  * [1]
β+.  ********* [9]
β–.  ***** [5]
electron capture.  **** [4]
γ.  * [1]
(Unsure/guessing/lost/help!)  **** [4]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"For antimatter, do paths always travel reversed (right-to-left) with respect to time?" (Yes, that's the convention we're using with these Feynman diagrams, although antimatter doesn't literally go backwards in time.)

"I really want to understand every single lessons that we did (even though I do okay in general) before learning new contents... It really bothers me to be so slow to understand the concepts."

"Please go over examples above."

20180505

Physics midterm question: decreasing capacitor charge

Physics 205B Midterm 2, spring semester 2018
Cuesta College, San Luis Obispo, CA

An electron is placed between the plates of a charged capacitor connected to an ideal 9.0 V emf source. Discuss whether the electron should move to the left or to the right between these plates in order to increase its electric potential energy. Explain your reasoning by using the properties of capacitors, charge, electric potential, and energy.

Solution and grading rubric:
  • p:
    Correct. Discusses why the charge stored in the capacitor will decrease because:
    1. the capacitance of the capacitor is constant, as it has been already constructed and thus its plate area and separation distance remain unchanged; and
    2. as the applied voltage ΔV decreases, because the capacitance remains constant, then the charge stored must also decrease.
  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Discusses (2), but assumes and does not explain (1) why capacitance is constant.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete. Assumes and does not explain why capacitance is constant, and somehow argues from C = QV how Q is inversely related to ΔV; or discusses how decreasing ΔV causes a decreasing Q because EPE decreases (from EPE = (1/2)⋅Q⋅ΔV), but does not discuss why EPE is expected to decrease (from EPE = (1/2)⋅C(⋅ΔV)2, where capacitance is constant).
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some attempt at applying properties of capacitors, charge, electric potential, and energy.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at systematically applying properties of capacitors, charge, electric potential, and energy.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 30882, 30883
Exam code: midterm02iFtW
p: 14 students
r: 8 students
t: 9 students
v: 2 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 4632):


Another sample "p" response (from student 3693):

Physics midterm question: comparing ammeter readings

Physics 205B Midterm, spring semester 2018
Cuesta College, San Luis Obispo, CA

Two separate circuits have an ideal 6.0 emf source connected to three resistors and an ammeter. Discuss which circuit will have a higher ammeter reading (or if there is a tie), and why. Explain your reasoning using Kirchhoff's rules, Ohm's law, and properties of ammeters.

Solution and grading rubric:
  • p:
    Correct. Discusses/demonstrates how the ammeter in circuit (a) will have a higher reading than in circuit (b) because:

    1. the equivalent resistance of circuit (a) is greater than the equivalent resistance of circuit (b), either by calculating their respective equivalent resistances:

      1. Req = [(1/2.0 Ω) + 1/(1.0 Ω + 1.0 Ω)]−1 = 1.0 Ω,

      2. Req = [(1/1.0 Ω) + 1/(1.0 Ω + 2.0 Ω)]−1 = 0.75 Ω; and

    2. since both circuits have the same emf of 6.0 V, then from Ohm's law, the current in circuit (a) (and its ammeter reading) will be lower than the current in circuit (b):

      1. Ⓐ = Icircuit = ΔVeq/Req = (6.0 V)/(1.0 Ω) = 6.0 A,

      2. Ⓐ = Icircuit = ΔVeq/Req = (6.0 V)/(0.75 Ω) = 8.0 A.

    (May also have recognized that the equivalent resistance of a parallel resistor system must be lower than the lowest single-resistor parallel branch (thus lower than the upper bound of 2.0 Ω for circuit (a), but lower than the upper bound of 1.0 Ω for circuit (b)); and then since the same emf is applied for both circuits (a)-(b), the the circuit with the lower equivalent resistance must have the higher ammeter reading.)

  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete.

    1. Typically garbles equivalent resistance calculations, for example:

      Req = [(1/2.0 Ω) + (1/1.0 Ω) + (1/1.0 Ω)]−1, or

      Req = 2.0 Ω + [(1/1.0 Ω) + (1/1.0 Ω)]−1, etc.,

      but still recognizes that both circuits have the same emf of 6.0 V, then applies Ohm's law to determine which circuit has more current consistent with their equivalent resistance calculations; or

    2. correctly or nearly correctly determines equivalent resistances, but does not clearly carry result into Ohm's law to determine which circuit has more current.

  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some attempt at applying properties of Kirchhoff's rules, Ohm's law, and properties of ammeters.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at systematically applying Kirchhoff's rules, Ohm's law, and properties of ammeters.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 30882, 30883
Exam code: midterm02iFtW
p: 14 students
r: 0 students
t: 16 students
v: 0 students
x: 4 students
y: 0 students
z: 0 students

A sample "p" response (from student 4444):

Another sample "p" response (from student 7744):

Physics midterm question: changing terminal voltage of real battery

Physics 205B Midterm 2, spring 2018
Cuesta College, San Luis Obispo, CA

A real battery with an emf of 6.0 V and internal resistance r is connected to a resistor R, and a voltmeter. An additional R resistor is then wired in series to this circuit. Discuss why the voltmeter will have a higher reading for the two-resistor circuit. (Assume that the internal resistance r of the battery remains constant.) Show your work and explain your reasoning using Kirchhoff's rules, Ohm's law, and properties of voltmeters.

Solution and grading rubric:
  • p:
    Correct. Discusses/demonstrates how voltmeter in case (b) will have a higher reading because:
    1. in both cases, the voltmeter will read the terminal voltage difference across the battery, where the battery's emf ε and internal resistance r are constant:

      Ⓥ = +ε − Icircuitr;

    2. and in circuit (a) more current will flow compared to circuit (b), as circuit (a) has less equivalent resistance than circuit (b):

      1. Icircuit = ΔVeq/Req,

        Icircuit = (6.0 V)/(r + R);

      2. Icircuit = ΔVeq/Req,

        Icircuit = (6.0 V)/(r + R + R);

    3. such that the voltmeter reading in circuit (a) will have a greater reading than in circuit (b):

      1. Ⓥ = +ε − Icircuitr = +6.0 V − (6.0 V)⋅(r/(r + R)),

        Ⓥ = (6.0 V)⋅(1 − (r/(r + R)));

      2. Ⓥ = +ε − Icircuitr = +6.0 V − (6.0 V)⋅(r/(r + R + R)),

        Ⓥ = (6.0 V)⋅(1 − (r/(r + 2⋅R))).

  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Two of points (1)-(3) complete and correct.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete. Has only one of (1)-(3) complete and correct.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some attempt at applying properties of Kirchhoff's rules, Ohm's law, and properties of voltmeters. Typically has current unchanged when additional R resistor is added, or argues that current increases, but Req = 2⋅R instead of r + 2⋅R for circuit (b).
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at systematically applying Kirchhoff's rules, Ohm's law, and properties of voltmeters.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.

Grading distribution:
Sections 30882, 30883
Exam code: midterm02iFtW
p: 6 students
r: 6 students
t: 9 students
v: 7 students
x: 6 students
y: 0 students
z: 0 students

A sample "p" response (from student 7164):

Physics midterm question: loop entering, leaving magnetic field

Physics 205B Midterm 2, spring semester 2018
Cuesta College, San Luis Obispo, CA

Within a certain region (shown in gray) there is an external uniform magnetic field, and the magnetic field is zero everywhere outside of this region. A square metal loop of resistance R moves with constant velocity as it enters, then exits this magnetic field region. Discuss why the induced current flows in one direction around the loop as it enters the magnetic field region, then flows in the other direction around the loop as it exits the magnetic field region. Explain your reasoning using the properties of magnetic fields, forces, motional emf, Faraday's law and Lenz's law.


Solution and grading rubric:
  • p:
    Correct. Explains how the induced current flows in one direction around the loop and in the other direction around the loop as it (a) enters and (b) exits the external magnetic field by using:
    1. RHR1, where the velocity direction of the loop (downwards) and external magnetic field direction (pointing into the page) result in a force on the fictitious positive charges to the right in both cases (a)-(b), but only in the horizontal portion of the loop that is inside the magnetic field, thus resulting in an induced current that is counterclockwise in (a) and clockwise in (b); or
    2. Faraday's law and Lenz's law, where moving the loop downwards would increase the magnetic flux going into the page through the loop in (a), and decreasing the magnetic flux going into the page through the loop in (b); and from Lenz's law, these changes in the magnetic flux through the loop will be "fought" by an induced current that must be flowing counterclockwise in (a), and clockwise in (b).
  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Directions of induced current are clockwise in (a), and counterclockwise in (b), but otherwise still systematically applies RHR1 or Faraday's law and Lenz's law.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some attempt at applying properties of magnetic fields, forces, motional emf, Faraday's law and Lenz's law.
  • x:
    Implementation of ideas, but credit given for effort rather than merit. No clear attempt at systematically applying properties of magnetic fields, forces, motional emf, Faraday's law and Lenz's law.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 30882, 30883
Exam code: midterm02iFtW
p: 12 students
r: 12 students
t: 1 student
v: 5 students
x: 4 students
y: 0 students
z: 0 students

A sample "p" response (from student 1712):

Another sample "p" response (from student 1929):