Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz06eL3k
Sections 30882, 30883 results
| 0- 6 : | * [low = 6] |
| 7-12 : | ***** |
| 13-18 : | ********************* [mean = 17.0 +/- 5.1] |
| 19-24 : | ********** |
| 25-30 : | * [high = 27] |
20160430
Physics quiz archive: magnetism, induction
Physics 205B Quiz 6, spring semester 2016
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz06eL3k
Sections 30882, 30883 results
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz06eL3k
Sections 30882, 30883 results
20160429
Online reading assignment: radioactive decay modes
Physics 205B, spring semester 2016
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.
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.
Explain what a "nucleon number" is, and/or describe how to calculate it for a nucleus.
Identify the processes that increase, decrease, or do not change the number of protons in the nucleus.
(Only correct responses shown.)
Identify the processes that increase, decrease, or do not change the number of neutrons in the nucleus.
(Only correct responses shown.)
Identify the processes that change a proton to a neutron, or change a neutron to a proton in the nucleus.
(Only correct responses shown.)
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
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.
"Protons and neutrons make up the nucleus. Greater than 83 protons, more protons than neutrons, or excess neutrons create instability. This can be stabalized in a few ways: alpha, beta minus, beta plus, and gamma decay."
"Contrails in a cloud chamber, produced by natural background radioactive decay particles passing through cold, alcohol-saturated air. Radioactive particles from natural background decays zing around all the time, whether or not the air just so happens to be cold and alcohol-saturated."
"We cannot count radio active atoms we can only count how many decayed atoms there are. Atoms decay randomly but we are able to give each isotope a half-life based on the number of daughters it produces during a period of time."
"The neutrons in the nucleus of an atom help to mitigate the repulsion forces the protons exert on themselves and helps keep the nucleus intact (strong force). A nucleus of an atom is stable only when the number of protons is slightly lower than or equal to the number of neutrons; if these conditions are not met, then the atom will undergo some sort of decay to stabilize the nucleus."
"What I was able to gather from the reading is that the 'backbone' of an atomic nuclei are the neutrons within the nucleus. As I learned in chemistry last semester (physics has made me question how much I can rely on what I learned) the number of protons in an atom is equal to the amount of neutrons (I say this reluctantly now). So even while protons repel from each other, the neutrons within the nucleus sort of balance out this repulsion so that the atomic nuclei itself can remain whole. Until there are 83 protons in which the amount of repulsion within the nuclei despite the amount of neutrons will subsequently result in an unstable nucleus. I know I'm talking about stuff that doesn't directly regard physics, however, I've been trying to dive into the chemistry we have been talking about because I'm realizing now that my chemistry class was even more basic than I had originally thought."
"What keeps together the nucleus in an atom is the attraction between the protons and the neutrons and the ratio of them is important (because neutrons turn into protons and vice versa WHAAAT!). When there are more than 83 protons than normal then alpha radiation occurs. When there are more protons in the ratio then beta minus occurs while a bunch more neutrons in the ratio causes beta plus radiation. After a nucleus returns from an excited state they still may have to much energy which they may release through gamma radiation."
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.
"It makes sense, but HOW. Magic repulsion and stickiness?"
"This presentation went very well. I really thought this presentation helped a lot, it even helped me understand whats going on in chemistry better thanks!"
"I am confused on how the electron capture is calculated. I don't know how to determine the number of protons or neutrons in the electron capture."
"What I found confusing about the reading is how the heck does a proton turn into a neutron and vice versa! More importantly how the heck is a neutron 'intrinsically' unstable!!! Physics is making me question the very little amount of things I know about chemistry."
"I'm mostly confused about the strong force that nucleons exert on each other that sticks them together. If a neutron has no charge...how can they possibly be attracted to anything? Or is this just something that isn't quite understood yet?"
"Nothing. I've got this chemistry on lock!"
Explain what a "nucleon number" is, and/or describe how to calculate it for a nucleus.
"The nucleon number denotes the total number of nucleons (protons and electrons), such that the number of neutrons is the difference between the nucleon number and atomic number."
"The total number of protons and neutrons. Z + N = A."
Identify the processes that increase, decrease, or do not change the number of protons in the nucleus.
(Only correct responses shown.)
α decay: decrease. [80%]
β– decay: increase. [74%]
β+ decay: decrease. [66%]
electron capture: decrease. [34%]
γ decay: does not change. [71%]
Identify the processes that increase, decrease, or do not change the number of neutrons in the nucleus.
(Only correct responses shown.)
α decay: decrease. [77%]
β– decay: decrease. [69%]
β+ decay: increase. [71%]
electron capture: increase. [26%]
γ decay: does not change. [74%]
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. [77%]
β– decay: n → p. [77%]
β+ decay: p → n. [74%]
electron capture: p → n. [29%]
γ decay: no p/n conversion. [80%]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"This stuff is basically alchemy. That's so awesome!"
"This antimatter electron twin stuff is freaky. Somebody should have Antman jump into a positron annihalating an electron and see which universe he ends up in."
"I need to start showing up to class again. I'm losing patience with this semester. Thank God we have three weeks left."
20160425
Online reading assignment: radioactive decay rates
Physics 205B, spring semester 2016
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.
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.
State the SI units for activity (radioactive decays per time).
For a radioactive decay process, the time constant τ ("average lifetime") is __________ half-life T1/2.
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.)
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
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.
"The 'activity' is the number of atoms that decay during a time interval. Half-life is the time it take for one-half of a sample to decay. The decay constant is the likelihood that a particular atom will decay in certain time interval. Finally, the time constant is the average lifespan of an atom in a sample."
"I understand quite a bit about half-life and radioactive decay. I've taken chemistry courses about the purposes behind radioactive dating and how to use the half life equations. That's essentially all it is, is understanding how to use the half life equations in certain situations to solve the problems. But i guess that's all what physics is. It is knowing which equation to use for each particular situation."
"Not much."
"I thought it was really interesting to find out how the older a substance is, the more daughter atoms it has. Also finding the age of the material was really interesting. It all has to do with the daughter atoms, something I didn't even know existed."
"Not sure what I do know."
"That radioactivity is a relation of atoms the are stablizing slowly or rapidly and give off energy as a result. I get that different elements will have different half-lives."
"Decay is exponential."
"In order to determine the rate at which radioactive nuclei disintegrate within an object is like taking me back to stats class; you basically have to collect data for a given amount of time until one can come up with a relative decay/activity rate that he/she is confident in. After this collection of data has been made then one can come up with a relative decay/activity constant which they can later reference."
"Radioactive decay counts the number of disintegrations per half-life. Each half life theoretically activates one-half of an isotope."
"In this case, R0 is the initial rate of decays per second at t = 0. We can use a Wolfram Mathematica template with our M&M™ data to find an expression for the decay constant λ, which for a statistically large sample is the probability that a given single M&M™ will decay in a given time interval. "
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 such as exponential and activity? I have no idea what is going on with the equations or constants. Help!"
"Nothing really confuses me in this section."
"What does e stand for in the decay equation?"
"I'm so lost I don't know what to ask"
"I feel I just need to reread the chapter a couple of more times, and I will really get it. It wasn't that difficult when I really sat down to it. All I need to do is practice more."
"I actually understand this stuff because of chemistry. :) Yay!"
"I thought that everything with the half life seemed pretty straight forward. Im still really confused by all of the hand rules and fields and stuff so I'm really trying to wrap my mind around that first before the quiz/midterm."
State the SI units for activity (radioactive decays per time).
"R(t)."
"Curies?"
"Lambda?"
"It is decays/sec."
"The SI unit for radioactivity is the becquerel (Bq)."
"The becquerel (Bq), one of which is one disintegration per second."
For a radioactive decay process, the time constant τ ("average lifetime") is __________ half-life T1/2.
less than. *** [3] equal to. ******** [8] greater than. ********************** [22] (Unsure/guessing/lost/help!) **** [4]
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: adioactive sample with daughter atoms. [57%]
"The radioactivity is what changes here."
"Can't say I know =/"
"Not sure sounds cool."
"Gaseous daughter atoms are trapped within a sample over time. When this sample is melted, then these gaseous daughter atoms are released and are compared to it's original non-daughter atom state. By melting the object, you are transforming the daughter atoms into a gaseous state and releasing them from the object they are trapped in. Once resolidified, there will not be any daughter atoms within the object."
"After a molten sample solidifies, it will start of again having radioactive atoms with no daughter atoms. So, melting a sample 'resets' its solidification age."
"When it is melted then solidified then the gaseous daughters are released. Because of this it resets the solidification age."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I assume it's no coincidence that this class and my chemistry class are almost always covering the same topic at the same time?" (But physics class will make it more fun.)
"Radioactive decay? I think I recall covering this in chemistry class. But that was ages ago."
"Honestly , I'm just ready for school to be over. I am so done with life!"
"When a sample is melted to restart the timer is that melting the daughter element/compound? Will the daughter atoms always be released in a gaseous form? If not, then would you not be able to date the material?" (Typically, the daughter elements are either helium or radon gas, which would bubble out and be released from the sample before it cools and hardens. These gases do not naturally occur inside of rocks unless they were produced by radioactive decays, so they can be used for radioactive dating. Other elements used for radioactive dating that aren't gaseous must specifically be daughter elements that would not naturally occur inside of a sample.)
"I understand we may get to eat some M&M™s in class? Other than that I am lost."
"I have a problem with eating M&M™s since I do not like chocolate." (#wut)
"I was really confused on what the solidification age of a substance tells us? I don't really get it." (It tells you how long it has been since that sample cooled and hardened. Geologists always want to know how long a sample has been solidified, as it reveals when a volcano last erupted, etc.)
"How did physicists/chemists before us determined the half-life of specific substances? I understand that they can collect data and perform a decay rate test, but how accurate are all of the tests done across the board?" (You don't even need to know how many radioactive atoms you have in your sample, you just need to record how the decay rate changes over time to find out the half-life of that atom. We'll do this with M&M™s, where we don't know their half-life, but we'll observe how they "decay" over time to do an exponential curve-fit to empirically find out the decay constant and their half-life. The larger your sample, the more accurate your half-life will be)
"Currently traveling at 36 m/s so I'm unable to complete this assignment at the moment." (80 mph? #wut)
20160423
Astronomy current events question: mass of galaxy NGC 1600's supermassive black hole
Astronomy 210L, spring semester 2016
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!)
(A) supernova explosions.
(B) passing gravitational waves.
(C) satellite dwarf galaxies.
(D) its spiral arms.
(E) velocities of stars near it.
Correct answer: (E)
Student responses
Sections 30678, 30679, 30680
(A) : 2 students
(B) : 6 students
(C) : 5 students
(D) : 6 students
(E) : 22 students
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 , "Behemoth Black Hole Found in an Unlikely Place" (April 6, 2016)The mass of the supermassive black hole in galaxy NGC 1600 was estimated by analyzing its gravitational effect on:
nasa.gov/feature/goddard/2016/behemoth-black-hole-found-in-an-unlikely-place
(A) supernova explosions.
(B) passing gravitational waves.
(C) satellite dwarf galaxies.
(D) its spiral arms.
(E) velocities of stars near it.
Correct answer: (E)
Student responses
Sections 30678, 30679, 30680
(A) : 2 students
(B) : 6 students
(C) : 5 students
(D) : 6 students
(E) : 22 students
Astronomy current events question: gaps in TW Hydrae's protoplanetary disk
Astronomy 210L, spring semester 2016
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!)
(A) the formation of planets.
(B) supernova shockwaves.
(C) due to gravitational waves.
(D) intermittent stellar winds.
(E) a passing black hole.
Correct answer: (A)
Student responses
Sections 30678, 30679, 30680
(A) : 28 students
(B) : 4 students
(C) : 5 students
(D) : 2 students
(E) : 1 student
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!)
Valeria Foncea , Charles E. Blue, Richard Hook, and Masaaki Hiramatsu , "ALMA's Best Image of a Protoplanetary Disk" (March 30, 2016)The Atacama Large Millimeter/submillimeter Array's images of rings and gaps in the disk surrounding the sun-like star TW Hydrae may be:
http://www.almaobservatory.org/en/press-room/press-releases/937-almas-best-image-yet-of-a-protoplanetary-disk
(A) the formation of planets.
(B) supernova shockwaves.
(C) due to gravitational waves.
(D) intermittent stellar winds.
(E) a passing black hole.
Correct answer: (A)
Student responses
Sections 30678, 30679, 30680
(A) : 28 students
(B) : 4 students
(C) : 5 students
(D) : 2 students
(E) : 1 student
Astronomy current events question: triple-star system planet KELT-4Ab
Astronomy 210L, spring semester 2016
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!)
(A) dimming of star brightnesses.
(B) gravitational waves.
(C) short radio wavelengths.
(D) coronal mass ejections.
(E) intermittent stellar winds.
Correct answer: (A)
Student responses
Sections 30678, 30679, 30680
(A) : 21 students
(B) : 5 students
(C) : 3 students
(D) : 9 students
(E) : 3 students
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!)
Brian Wallheimer, "Astrophysicists Find Triple Star System with 'Hot Jupiter'" (April 7, 2016)Preliminary observations of __________ by the Kilodegree Extremely Little Telescope led to the discovery of planet KELT-4Ab in a three-star system.
news.nd.edu/news/65993-astrophysicists-find-triple-star-system-with-hot-jupiter/
(A) dimming of star brightnesses.
(B) gravitational waves.
(C) short radio wavelengths.
(D) coronal mass ejections.
(E) intermittent stellar winds.
Correct answer: (A)
Student responses
Sections 30678, 30679, 30680
(A) : 21 students
(B) : 5 students
(C) : 3 students
(D) : 9 students
(E) : 3 students
Physics quiz question: percent decrease in radioactivity
Physics 205B Quiz 7, Spring Semester 2011
Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 29.33(c)
Consider fluoride-18, (which is injected into patients undergoing a positron emission tomography (PET) scan), which decays via β+ decay with a half-life of 110 minutes. What is the percent decrease in activity for a sample of during a PET scan, which takes 30 minutes?
(A) 0.91%.
(B) 1.3%.
(C) 17%.
(D) 24%.
Correct answer: (C)
The activity of a sample is given by:
R = R_0*(1/2)^(t/T),
where T is the half-life. Solving for the activity at t = 30 minutes, assuming that R_0 will be normalized to 1:
(R/R_0) = (1/2)^(t/T) = (1/2)^(30 minutes/110 minutes) = 0.8278,
So the percent decrease in 30 minutes will be 1 - 0.8278 = 0.1722, or 17%.
Response (A) is 1/T; response (B) is the time constant tau = 1/(T*ln(2)); response (D) is 1 - exp^(-30/110), presumably confusing T with tau in the exponential decay formula.
Section 30882
Exam code: quiz07t0LO
(A) : 0 students
(B) : 0 students
(C) : 6 students
(D) : 2 students
"Success level": 75%
Discrimination index (Aubrecht & Aubrecht, 1983): -0.50
Compare to an older version of this question from Fall 2010.
Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 29.33(c)
Consider fluoride-18, (which is injected into patients undergoing a positron emission tomography (PET) scan), which decays via β+ decay with a half-life of 110 minutes. What is the percent decrease in activity for a sample of during a PET scan, which takes 30 minutes?
(A) 0.91%.
(B) 1.3%.
(C) 17%.
(D) 24%.
Correct answer: (C)
The activity of a sample is given by:
R = R_0*(1/2)^(t/T),
where T is the half-life. Solving for the activity at t = 30 minutes, assuming that R_0 will be normalized to 1:
(R/R_0) = (1/2)^(t/T) = (1/2)^(30 minutes/110 minutes) = 0.8278,
So the percent decrease in 30 minutes will be 1 - 0.8278 = 0.1722, or 17%.
Response (A) is 1/T; response (B) is the time constant tau = 1/(T*ln(2)); response (D) is 1 - exp^(-30/110), presumably confusing T with tau in the exponential decay formula.
Section 30882
Exam code: quiz07t0LO
(A) : 0 students
(B) : 0 students
(C) : 6 students
(D) : 2 students
"Success level": 75%
Discrimination index (Aubrecht & Aubrecht, 1983): -0.50
Compare to an older version of this question from Fall 2010.
20160422
Online reading assignment: flux laws & devices
Physics 205B, spring semester 2016
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.
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.
State/describe the symbol used for magnetic flux, and give its SI units.
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.)
(Only correct responses shown.)
(Only correct responses shown.)
Explain why a transformer that has the same number of primary coils and number of secondary coils would not be useful.
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
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.
"For an ideal transformer, power in = power out."
"We are using two magnetic flux laws to analyze generators: Faraday's and Lenz's."
"A current is induced through a wire loop when the magnetic flux through it is changing (as described by Faraday's law). The current induced in the loop will be in the direction that creates a magnetic field opposing the change in magnetic flux (Kind of like how an object resists a change in motion). A transformer is made of a primary coil and a secondary coil; by rapidly changing the current in the primary coil the magnetic flux through the secondary coil is constantly changing which induces an emf on it."
"I do understand how to apply Faraday's law and the magnetic flux maybe."
"Faraday's law is a statement that an induced emf ε occurs in a wire loop while the magnetic flux ΦB through it changes, whether the magnetic field gets stronger or weaker, or by changing the orientation of the surface such that more or fewer magnetic field lines go 'through' the surface. If the magnetic flux ΦB is constant or unchanging, then there is no induced emf in the wire loop."
"When there is a changing magnetic flux there is a emf. That is Faraday's law. The more coils the more emf."
"I understand the concept behind the sliding rail generator. As the rod moves it creates an induced emf and the faster it moves the greater the emf but when it is stationary no emf is produced."
"For any imaginary or actual area A in the presence of a (uniform magnitude and direction) magnetic field B, the magnetic flux ΦB is the product of the magnetic field magnitude B and the area A. The perpendicular symbol "⊥" denotes that the maximum value for magnetic flux ΦB occurs if the magnetic field lines are perpendicular to the surface and ΦB would be zero if the magnetic field is parallel to the surface (as no magnetic field lines would actually go "through" the surface)."
"Magnetic flux is determined by the magnetic field and area and this value is greatest when magnetic field is perpendicular to surface. There is no induced emf when a magnetic flux is constant or unchanging, and the amount of emf depends on the number of coil turns."
"Magnetic flux is the product of the magnetic field and the area."
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.
"Why does the magnetic flux have to not be constant to induce an emf?"
"Magnetic flux really has me in nowhereland."
"I found the induction forge example a little confusing. I'm having a hard time grasping the concept of magnetic flux and how it creates heat in this context."
"What exactly is magnetic flux, and how is it different from a magnetic field or magnetic force?"
"I'm not sure if I really understood Lenz's law."
"I am having some confusion in the explanation of the two rules are applied to the objects pictured in the presentation of Lenz's law and Faraday's law."
"What I had trouble with in this reading was understanding Faraday's law, and what can be explained from using it. I can see that as time changes a magnetic flux may change through a loop of wire, but I am very much confused with where to go from there. The most definitive thing I can say about Faraday's law is that uses the average time rate of change of the flux that passes through a loop."
"I have no idea what is going on in class and that is purely my fault. Hope I get caught up."
"I do not get the Lenz's law and the transformers section of the online presentation."
"I really thought that this presentation was interesting to read, I honestly need to read into it more and do more of the example problems to get a better understanding of the concepts in it though."
"Pretty much everything to be honest, I read the blogs and I like to tell myself that it makes it easier to see it again in class because I don't understand anything while reading."
"I'm still confused on how to interpret the rotating-coil generator, I'm just not sure how to apply the RHR's to these scenarios correctly. I always seem to be off in the placement/ orientation of my palm. I'll have my fingers correct but my palm will be facing the wrong direction, which changes the orientation of at least one of the units marked on my fingers."
"I am unsure about the 'step-down and step-up' operations of transformers. My roommates tried to explain it to me (they are engineers). But I need more clarification or applicable knowledge about the use of transformers."
"I'm pretty confused on what exactly magnetic flux is. That being said I'm also confused on the whole concept of Faraday's law."
"I started to get really confused starting at the generators part and then was totally lost by the end of the presentation. I really need to see some practice problems for this section."
"I'm not sure I understand what 'step-down/step-up' means. I could use some clarification and maybe visuals of what is supposed to be happening with that."
State/describe the symbol used for magnetic flux, and give its SI units.
"Phi, webers, or something like that. #idk I was never in a frat."
"ΦB is the symbol, which is the product of the magnetic field magnitude B and the area A."
"'Phi sub B,' teslas times meters squared, or webers."
"Units are webers, Wb. And the symbol is an oval with a vertical line through it with a subscript B."
"Circle with a line through it. Webers."
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 [72%]
Constant non-zero magnetic flux: no induced current in loop. [47%]
Magnetic flux increasing in strength: induced current in loop. [72%]
Magnetic flux decreasing in strength: induced current in loop. [61%]
(Only correct responses shown.)
Current: stepped-up (increases). [36%]
Power: no change. [39%]
(Only correct responses shown.)
Current: stepped-down (decreases). [50%]
Power: no change. [44%]
Explain why a transformer that has the same number of primary coils and number of secondary coils would not be useful.
"It needs to either step-up or step-down to be useful."
"The induced emf would just be the same if there was the same number of coils."
"It would not be useful because nothing would be transformed. There would be no difference."
"It won't allow to stepped-down or stepped-up. Making it to different numbers will be very useful for the transformer."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Do the other instructors call you 'P-dog' as well?" (Only my graduate student teaching assistants at UC-Davis, and they meant it only ironically.)
"This just seems to be getting harder and harder every time!"
"Explain why transformers are more efficient at high frequency as in an inverter welder." (A constant magnetic flux does not induce an emf. Changing the magnetic flux induces an emf. Changing it rapidly (with a high frequency) will induce more emf.)
"I was sort of confused on the questions regarding the stepping-up and stepping-down of a transformer."
"I HATE MY LIFE RIGHT NOW BECAUSE I'M STILL STUCK ON CIRCUITS!"
"Can you go over magnetic flux?"
"Why are electrons affected by magnets? Like, what is happening in a permanent magnet that pulls an electron like that?" (Electrostatics is how stationary charges exert forces on each other. On the other hand, magnetism is how moving charges exert forces on each other. A single moving charge, or current flowing through a wire, or the unpaired electron spins in the outermost atomic shell in a permanent magnet (like↑↓↑↑↑) create magnetic fields (step 1 of the two-step process). Then magnetic fields exert force on a single moving charge, or current flowing through a wire, or on the unpaired electron spins in a permanent magnet (step 2 of the two-step process).)
20160421
Astronomy quiz question: Lagoon Nebula colors
Astronomy 210 Quiz 6, spring semester 2016
Cuesta College, San Luis Obispo, CA
ESO/VPHAS+ team
eso.org/public/usa/images/eso1403a/
[Version 1] The Lagoon Nebula (Messier 8/NGC 6523) is observed to have regions of pink and dark brown colors. The composition of its pink color regions is:
(A) helium gas.
(B) hydrogen gas.
(C) very small dust particles.
(D) dense clumps of large dust particles.
Correct answer (highlight to unhide): (B)
The pink colors are the combination of red, violet, and blue photons given off by excited hydrogen electrons jumping down to lower orbitals.
Section 30674
Exam code: quiz06ncM7
(A) : 4 students
(B) : 9 students
(C) : 7 students
(D) : 0 students
Success level: 48% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.20
[Version 2] The Lagoon Nebula (Messier 8/NGC 6523) is observed to have regions of pink and dark brown colors. The composition of its dark brown color regions is:
(A) helium gas.
(B) hydrogen gas.
(C) very small dust particles.
(D) dense clumps of large dust particles.
Correct answer (highlight to unhide): (D)
The dark brown color is due to large, clumpy dust particles blocking visible light.
Section 30676
Exam code: quiz06sRR0
(A) : 1 student
(B) : 5 students
(C) : 7 students
(D) : 35 students
Success level: 74% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.29
Cuesta College, San Luis Obispo, CA
ESO/VPHAS+ team
eso.org/public/usa/images/eso1403a/
[Version 1] The Lagoon Nebula (Messier 8/NGC 6523) is observed to have regions of pink and dark brown colors. The composition of its pink color regions is:
(A) helium gas.
(B) hydrogen gas.
(C) very small dust particles.
(D) dense clumps of large dust particles.
Correct answer (highlight to unhide): (B)
The pink colors are the combination of red, violet, and blue photons given off by excited hydrogen electrons jumping down to lower orbitals.
Section 30674
Exam code: quiz06ncM7
(A) : 4 students
(B) : 9 students
(C) : 7 students
(D) : 0 students
Success level: 48% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.20
[Version 2] The Lagoon Nebula (Messier 8/NGC 6523) is observed to have regions of pink and dark brown colors. The composition of its dark brown color regions is:
(A) helium gas.
(B) hydrogen gas.
(C) very small dust particles.
(D) dense clumps of large dust particles.
Correct answer (highlight to unhide): (D)
The dark brown color is due to large, clumpy dust particles blocking visible light.
Section 30676
Exam code: quiz06sRR0
(A) : 1 student
(B) : 5 students
(C) : 7 students
(D) : 35 students
Success level: 74% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.29
Astronomy quiz question: old star cluster with red dwarfs
Astronomy 210 Quiz 6, spring semester 2016
Cuesta College, San Luis Obispo, CA
Red dwarfs and __________ will be found in an old star cluster.
(A) massive main-sequence stars.
(B) medium mass protostars.
(C) white dwarfs.
(D) supergiants.
Correct answer (highlight to unhide): (C)
All stars in a star cluster are born at the same time, but undergo stellar evolution at different rates depending on their masses. Red dwarfs are low mass stars in their main-sequence stage, and evolve slower than medium-mass stars, and much slower than massive stars. So this old star cluster will have massive stars that have already gone through their protostar, main-sequence, supergiant and type II supernova stages; and also have medium-mass stars that have already gone through through protostar, main-sequence, giant, planetary nebula, and white dwarf stages.
Section 30674
Exam code: quiz06ncM7
(A) : 3 students
(B) : 5 students
(C) : 10 students
(D) : 2 students
Success level: 53% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.20
Section 30676
Exam code: quiz06sRR0
(A) : 9 students
(B) : 9 student
(C) : 26 students
(D) : 4 students
Success level: 55% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.43
Cuesta College, San Luis Obispo, CA
Red dwarfs and __________ will be found in an old star cluster.
(A) massive main-sequence stars.
(B) medium mass protostars.
(C) white dwarfs.
(D) supergiants.
Correct answer (highlight to unhide): (C)
All stars in a star cluster are born at the same time, but undergo stellar evolution at different rates depending on their masses. Red dwarfs are low mass stars in their main-sequence stage, and evolve slower than medium-mass stars, and much slower than massive stars. So this old star cluster will have massive stars that have already gone through their protostar, main-sequence, supergiant and type II supernova stages; and also have medium-mass stars that have already gone through through protostar, main-sequence, giant, planetary nebula, and white dwarf stages.
Section 30674
Exam code: quiz06ncM7
(A) : 3 students
(B) : 5 students
(C) : 10 students
(D) : 2 students
Success level: 53% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.20
Section 30676
Exam code: quiz06sRR0
(A) : 9 students
(B) : 9 student
(C) : 26 students
(D) : 4 students
Success level: 55% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.43
Astronomy quiz archive: stellar evolution
Astronomy 210 Quiz 6, spring semester 2016
Cuesta College, San Luis Obispo, CA
Section 30674, version 1
Exam code: quiz06s7ll
Section 30674
Section 30676, version 1
Exam code: quiz06nUm6
Section 30676
Cuesta College, San Luis Obispo, CA
Section 30674, version 1
Exam code: quiz06s7ll
Section 30674
| 0- 8.0 : | |
| 8.5-16.0 : | ***** [low = 12.0] |
| 16.5-24.0 : | ***** [mean = 23.4 +/- 6.2] |
| 24.5-32.0 : | ******** |
| 32.5-40.0 : | ** [high = 33.0] |
Section 30676, version 1
Exam code: quiz06nUm6
Section 30676
| 0- 8.0 : | |
| 8.5-16.0 : | ******* [low = 8.5] |
| 16.5-24.0 : | ************ |
| 24.5-32.0 : | ****************** [mean = 25.7 +/- 6.2] |
| 32.5-40.0 : | *********** [high = 40.0] |
20160420
Online reading assignment: the Milky Way (SLO campus)
Astronomy 210, spring semester 2016
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.
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
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?
Using the most powerful light-gathering optical telescopes in the darkest skies, __________ of the stars in our entire galaxy can be observed from Earth.
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?
Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
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.
"Dark matter is interesting, this may or may not stem from my love of Futurama."
"hat the sun orbits around in Milky Way, this was interesting because the sun is usually seen as the center of the orbits."
"That we can calculate how far we are from the center of our galaxy. I never really wondered where we are situated in our galaxy before."
"I find dark matter interesting, mostly because we can't see it, but we can feel its effects."
"The traffic jam example explaining spiral arm formation was very interesting. I feel I learned a lot purely from that and the example made it much easier to understand."
"That a big chunk of our galaxy is made up of dark matter we can not see. I would think someone would have done a lot of research on dark matter by now to figure out what it is."
"It's interesting how much of the universe is dark matter and how so many people don't know and may not ever bother to know or care."
"How we figured out that our galaxy is shaped as a disk."
"How dark matter is like an unknown form of matter and yet, it's astonishing how it's still a problem today in astronomy."
"How stars in the Milky Way's spiral arms are being born, live for a short period, die continuously and then are reborn again, repeating."
"Learning about the Milky Way because I didn't really know anything about it before. I knew it was important before, but my non astronomy self just thought it was something cool to look for in the sky at night."
"The formation of stars in the spiral arms. The diagram is really cool in the textbooks as it shows how the stars are formed and then released out of the spiral orbit."
"That we are not 100% sure what the dark matter within the Milky Way is. This is interesting to me because most of matter could be made of of material we have not discovered."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Dark matter."
"I don't understand how the location of globular clusters tells us how close/far we are from the center of our galaxy. It just doesn't make sense to me."
"I didn't understand the bad hair day question."
"I don't entirely understand what the Cepheid variable stars are and was hoping you could explain more in depth of those!"
"I'm confused still about how dim red dwarfs are related to dark matter (and MACHOs in general), I thought dark matter doesn't interact with light or other forms of light matter."
"ow does dark matter accumulate so much mass evenly in our galaxy - if there are different areas of mass "evenly" spread out, say, black holes, or dim red dwarfs, or more of the MACHO / WIMP analogies, wouldn't there still be areas where light wouldn't pass by?"
"The part about density waves was confusing to me. I didn't understand the cause and effect of gravitational interactions."
"I'm pretty confused on the way we can tell the size and shape of the Milky Way."
"I think it's confusing why we have all these theories about our galaxy but no one can prove them to be completely true. I feel with our technology we should have been able to do that by now."
"How we know about dark matter."
"I know that we are a disk-shaped galaxy, but how do we really know if we are a spiral galaxy or or not?"
"I thought the slide of gravity and orbits was confusing. If the outer orbits are not as quick as the inner orbit speed does that mean that most of the mass of the Milky Way is not at the center?"
"The self-sustaining star formation was a little confusing to me."
"I'm not sure if I fully understand the spiral arms concept. I think I mostly get it. The density waves cause the stars to keep forming in the spiral arms, but I guess what I don't understand is what those density waves even are?"
"Radio wave maps. What???"
"Gravity and orbits of different Milky Way models. It's little hard to tell which one is concentrated in the center and which one is the inner orbits have the same speed as the outer orbits. As I can see they are just a tiny bit different."
"Dark matter is confusing. I don't understand how something can exist, but you can't see it. It should be called invisible matter or something!"
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. **************** [16] Not very much. *************** [15] Barely seen it. ********** [10] (Never been able to see it.) **** [4] (Unsure/guessing/lost/help!) ** [2]
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%. ********* [9] 5%. [0] 10%. ************************** [26] 50%. *** [3] 100%. * [1] (Unsure/guessing/lost/help!) ******** [8]
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's camera ;)"
"Look into a nearby meadow or stream and channel your inner Narcissus."
"Car window."
"ask your fellow campers."
"To be honest, who cares? I'd just leave my hair alone in a mess or wear a beanie."
"Nothing, because you are camping, and how your hair looks is not important."
"If you're worried about how your hair looks while you're camping then you aren't experiencing it and enjoying it as you should."
"Look at your shadow!"
"Physically touch your hair and try to visualize what it might look like based off what you normally want your hair to look like."
Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.
"The wheels are lined with a lot of LED lights, which strobe in a pattern at a speed matched by the movement of the wheel, resulting in what appears to be a still, LED image."
"They use a strip of colored lights in the wheel. When the wheel is rotating, it appears like the entire wheel is colored."
"The rapidly blinking lights coordinate to create patterns when moving across our field of view."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Did you buy the MonkeyLectric Rims specifically for this class? Will the multiple-choice portion of the midterm be composed of the same questions from the quizzes? Will we get a study guide for the final?" (Yes, yes, and yes.)
"I never go camping." (Then consider glamping.)
"Is this pink moon and green moon stuff real? On the 20th I heard it will be a green moon, and on the 22nd will be the pink moon." (I would hope that you have learned enough astronomy to determine whether stuff like this is true or not.)
"How do the PimpStar Rims know when they turn on a specific light? In other words, what mechanism is used to detect the location of the light?" (Probably an accelerometer sensor, the same way your phone knows whether it's right-side up, sideways, or upside-down.)
"No comment. (You just did.)
"Have you visited NASA?" (A few years back, I was the guest moderator for a NASA teaching education organization. #nasastrong #presenting #representing.)
"For some reason astronomy is a very abstract for me, and I have such troubles understanding any of it. Yet I still am so interested I wish I did not have so many units so I could really try and dedicate a lot of time to this class because it is very cool."
"I've failed every quiz, but I feel like I've learned a lot so that's good!"
"Do you have PimpStar Rims?" (Only on my bicycle. #theyseemerolling #theybehating)
20160419
Online reading assignment: the Milky Way (NC campus)
Astronomy 210, spring semester 2016
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.
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
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?
Using the most powerful light-gathering optical telescopes in the darkest skies, __________ of the stars in our entire galaxy can be observed from Earth.
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?
Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
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.
"That the halo of a galaxy is made up of mostly made old stars."
"Dark matter."
"I never knew where the spiral arms came from in the Milky Way. That's cool."
"The size of the Milky Way, I had no idea it was that big."
"Finding out what 'shape' the Milky Way is."
"MACHOs and WIMPs--something I can easily remember and very creative, P-dog! :)"
"That the Milky Way's arms are consisted of massive stars. Also, how these stars are constantly being born and dying, which in the end makes it appear as if it has arms."
"I am pretty inept when it comes to chemistry and science in general, but I am pretty interested in how massive stars can fuse to iron and explode."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"How luminosity is related to the pulsation period, which could be used to measure the distance of globular clusters."
"Dark matter."
"I could use more clarification on why we see the Milky Way the way we see it."
"Far-IR/ Radio wave maps."
"Spiral arm formation theories and trying to identify the maps and how they work."
"Density waves."
"How white dwarfs aren't really stars but compact objects."
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. ** [2] 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%. * [1] 5%. ** [2] 10%. **** [4] 50%. [0] 100%. * [1] (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?"It's camping. Just put a hat on or something."
"Ask a friendly wild forest animal."
"If I'm camping, it's a given I'm definitely having a bad hair day. Ha. ; )"
"Use my phone camera, or ask whoever I was camping with, or look for a body of water that I could see my reflection in. Of course, all I would really need to do is go to my car and look in either the rear view or side mirrors."
"I would look at my shadow. My hair is always bad though, so I guess it doesn't make a difference."
"Feel hair for knots, frizz, or the feeling of greasy hair.
Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.
"PimpStar Rims can display images as they spin via wifi, can have all with the same image or different images. MonkeyLectric Rims seems to be rims that come with a display already chossen that works as you cycle."
"The rims have lights on them that flash in certain patterns to form words of images while the wheel is spinning."
"Like the stars in the galaxy die out and others form in a consistent pattern, so do the lights of the wheels turn on and off in a pattern, forming an image."
"Our eyes get adjusted to the speed of how they are moving to the point where it doesn't see it spinning anymore."
"Blinking lights."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Your bike is awesome."
"I don't really enjoy real camping. However if were glamping I'm all there." (When Mrs. P-dog and I go camping, we are all about glamping with mirrors.)
"Apparently on April 20th there will be a 'green moon,' where the moon will appear green for 90 minutes every 420 years due to the alignment of several planets. Is this true? This is posted on Facebook, so it has to be true--Facebook is just about as credible as Wikipedia. (I trust that you now know enough astronomy to figure this out on your own.)
20160418
Online reading assignment: generators
Physics 205B, spring semester 2016
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.
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.
Explain what a generator is supposed to "generate."
Explain the meaning of "motional" in the term "motional emf."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
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 changing magnetic field, a changing area of a source, and a source moving in a magnetic field all induce an emf in the source, which induces a current in the source. When an emf is induced using a magnetic field it is called electromagnetic induction."
"One thing that I understand and found interesting is that, moving a rod through a magnetic field makes the rod a battery!"
"I understand how to do RHR1. RHR2 I'm a little confused on. I don't know when to use which."
"I understand the concept of generators but I couldn't make one if you asked me to."
"Motional emf is created from potential difference that happens when rods are passed through a magnetic field. this provides current."
"As long as the moving rod is moving through an electric field, the bottom end of the rod will be negative. In this case, the top rod will be positive."
"A continuous rotational generator acts similar to that of an object experiencing an ideal rotational inertia. As a magnet rests along side a constant rotating disc, the magnetic field that is provided as wires are connected to the axis and edges of the of the disc remains constant as expected. But the rotational movement of the disc allows for the amount of electric potential energy supplied by the generator to remain constant as well. It gives a decent idea as to how a standard generator is made."
"You can create emf by moving a metal rod or coil through magnetic fields."
"'Continuous' generators do not explicitly need to be reset in order to continuously provide motion emf and current. While 'single-pass' generators can only be used once before having to be reset."
"A generator uses magnetic field and a moving object to generate electric potentials. A rail generator needs to be stopped and reset. A rotational generator can infinitely spin."
"he rail generator has a rod made to move through a magnetic field while the ends of the rod rest on rails to make a complete circuit."
"We are going to eventually see some examples in class about RHR and how they apply to generators. There are single pass generators when a rod slides along a rail or a wire loop enters a magnetic field which need to rest after one use. There are also continuous generators which don't need resetting and theyre discs and coils that you just keep on rotating."
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 know I'm probably being slow, but I'm still a little tripped up about when to use which hand rules. For the problems on this page we need to use two each, right? One to first find the current and then another to find the magnetic field force? Are all of the hand rules and the situations that they're applicable in listed in one place somewhere? I need to just sit down and stare at them."
"I find the continuous generators to be a little tricky. I'm not quite sure how much they differ from other generators."
"I am still confused on generators. Is it generating electricity? I would think so because when the lights go out, they say go look for the generator to bring the power back."
"I could definitely use some good discussion on recent topics just to solidify concepts."
"I am confused on how to find out the direction of the magnetic field with a rotating rod. I am confused on what 'motional' means."
"So I think I understand the rail example with the snowboard however you lost me with the next example with the loops, where a wire loop encounters the edge of a uniform magnetic field. 'As long as some part of the loop is still entering the magnetic field, there will be a motional emf that will produce current in the loop, until the loop is completely inside of the magnetic field. Practically speaking, at some point you would need to stop the loop after it has completely entered the magnetic field, and bring it back out of the magnetic field--this would still generate a motional emf and current, but with opposite polarity, in order to 'reset' the system.' I don't understand this, completely lost here..."
"I found the rotating coil generator a little confusing. What is the benefit of a coil vs a ring/disk? More surface area?"
"When you use RHR1 and RHR2. How do you know when to use which one?"
"Single-pass generators are weird. I don't understand why you wouldn't just use a continuous generator."
"Not sure when to apply the different hand rules."
"What I found confusing about the reading was understanding a rail generator. I can understand how an electric charge can be provided to a generator as an object slides along a rail enough to provide a charge. However, I found it confusing as to why a generator would ever be constructed in this way, I just don't how you can make the electric potential applied to the generator constant. An explanation would be chill."
"The hoop drag generator is hard for me to understand and visualize in my head."
"Does the ε = vBL equation in the presentation preview equal the amount of motional emf produced? And if so does how much can that amount vary. Will we have to use that equation in the future? I don't understand how simply moving a rod through a magnetic field can generate current.eI did not find the material confusing, except some review of the material to see if I understand it would be nice.eI don't get how to use the RHRs for the rods. Can you go over these in class?"
"I also am still really confused about what we covered in class on Friday with the right hand rules and fields and I didn't feel like we had enough time for questions about the worksheet before class ended."
up ↑. ************* [13] down ↓. ******* [7] left ←. ** [2] right →. ***** [5] into the page ⊗. * [1] out of the page ⊙. * [1] (No direction, as this quantity is zero.) * [1] (Unsure/guessing/lost/help!) **** [4]
in towards the center of rotation. *** [3] out away from the center of rotation *************** [15] into the page ⊗. *** [3] out of the page ⊙. ** [2] (No direction, as this quantity is zero.) * [1] (Unsure/guessing/lost/help!) ********** [10]
Explain what a generator is supposed to "generate."
"Converts mechanical energy into electrical energy."
"Voltage?"
"I wasn't too sure, but don't they generate electricity? And since it generates electricity, it generates current."
"A generator is suppose to generate current and motional emf. Ultimately creating power."
Explain the meaning of "motional" in the term "motional emf."
"A motional emf is produced by moving an object through a magnetic field."
"Motion refers to the motion of charges in a conductor, moving through a magnetic field. This emf only exists as long as the conductor moves."
"'Motional' means something is moving, so its emf is generated by movement."
"I have no idea what it is supposed to mean. I don't understand this concept at all."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Mondays make me sad."
"Someone made fun of me at work when doing RHRs lol." (You're just presenting and representing. No shame.)
"Do many generators use magnetism?" (Only because magnetic fields exert forces on moving charges, so it is a very convenient way to change kinetic energy into making electric currents flow.)
"I am so behind in your class! I'm freaking out!" (I'm freaking out too! ≡:O Let's all try to get unfreaked out this week.)
"I was actually confused with what a generator is supposed to generate. I really don't know, I just assumed that it supplies a steady amount of volts but an explanation on that would be nice." (Yes, some generators produce a steady amount of volts (DC, or direct current generators), while some others produce an oscillating amount of volts (AC, or alternating current generators); but the main idea is that the volts generated will produce a current to flow in a useful circuit containing light bulbs, etc.)
20160417
Astronomy current events question: supernova "shock breakout"
Astronomy 210L, spring semester 2016
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!)
(A) formed a companion star.
(B) vaporized its inner planets.
(C) passed in front of a black hole.
(D) exploded as a type II supernova.
(E) was impacted by a meteor or comet.
Correct answer: (D)
Student responses
Sections 30678, 30679, 30680
(A) : 3 students
(B) : 0 students
(C) : 3 students
(D) : 26 students
(E) : 7 students
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!)
H. Pat Brennan and Michele Johnson, "Caught For The First Time: The Early Flash Of An Exploding Star" (March 21, 2016)NASA's Kepler space telescope detected the shockwave from a supergiant as it:
nasa.gov/feature/ames/Kepler/caught-for-the-first-time-the-early-flash-of-an-exploding-star
(A) formed a companion star.
(B) vaporized its inner planets.
(C) passed in front of a black hole.
(D) exploded as a type II supernova.
(E) was impacted by a meteor or comet.
Correct answer: (D)
Student responses
Sections 30678, 30679, 30680
(A) : 3 students
(B) : 0 students
(C) : 3 students
(D) : 26 students
(E) : 7 students
Astronomy current events question: neighborhood micrometeorite collection
Astronomy 210L, spring semester 2016
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!)
(A) tap water.
(B) composted plant material.
(C) rain gutter downspouts.
(D) volcanic ash.
(E) ocean floor sediments.
Correct answer: (C)
Student responses
Sections 30678, 30679, 30680
(A) : 7 students
(B) : 3 students
(C) : 21 students
(D) : 3 students
(E) : 5 students
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!)
Jennifer Hackett, "How to Find Tiny Meteorites at Home" (April 1, 2016)Micrometeorites can be extracted at home using a magnet on material collected from:
scientificamerican.com/article/how-to-find-tiny-meteorites-at-home/
(A) tap water.
(B) composted plant material.
(C) rain gutter downspouts.
(D) volcanic ash.
(E) ocean floor sediments.
Correct answer: (C)
Student responses
Sections 30678, 30679, 30680
(A) : 7 students
(B) : 3 students
(C) : 21 students
(D) : 3 students
(E) : 5 students
Astronomy current events question: recent impact on Jupiter
Astronomy 210L, spring semester 2016
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!)
(A) solar flare.
(B) undiscovered ring system.
(C) moon eclipse.
(D) meteor or comet impact.
(E) massive lightning storm.
Correct answer: (D)
Student responses
Sections 30678, 30679, 30680
(A) : 1 student
(B) : 1 student
(C) : 2 students
(D) : 20 students
(E) : 5 students
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!)
Phil Plait, "Jupiter Got Whacked by Yet Another Asteroid/Comet!" (March 29, 2016)Amateur astronomers in Europe recently observed a bright flash on Jupiter, which may have been caused by a(n):
slate.com/blogs/bad_astronomy/2016/03/29/jupiter_hit_by_asteroid_or_comet_in_march_2016.html
(A) solar flare.
(B) undiscovered ring system.
(C) moon eclipse.
(D) meteor or comet impact.
(E) massive lightning storm.
Correct answer: (D)
Student responses
Sections 30678, 30679, 30680
(A) : 1 student
(B) : 1 student
(C) : 2 students
(D) : 20 students
(E) : 5 students
Physics quiz archive: circuits (2)
Physics 205B Quiz 5, spring semester 2016
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz05Tt1p
Sections 30882, 30883 results
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz05Tt1p
Sections 30882, 30883 results
| 0- 6 : | |
| 7-12 : | *** [low = 12] |
| 13-18 : | ************** |
| 19-24 : | ************* [mean = 20.8 +/- 5.0] |
| 25-30 : | ******** [high = 30] |
20160415
Online reading assignment: magnetic fields of current-carrying wires and loops
Physics 205B, spring semester 2016
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 magnetic fields of current-carrying wires and loops.
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.
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.
State/describe the symbol used for the "permeability of free space," and give its SI units.
State whether it is possible or not possible for the following pairs of objects to exert magnetic forces on each other.
(Only correct responses shown.)
(Only correct responses shown.)
(Only correct responses shown.)
Explain the similarities/differences between a circular current loop, and a solenoid.
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
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 magnetic fields of current-carrying wires and loops.
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.
"How to do RHR2 and RHR3. Yay! (Palm straight, fingers curled, and thumb up for both. For RHR2 the thumb represents v or L, the line of the palm represents r, and the tips of the fingers represent B. For RHR3, the thumb represents B, the line of the palm still represents r, and the tips of the fingers represent current I.)"
"A source object creates a magnetic field everywhere around it: B, and it exerts a force on a test object."
"Current carrying wires that are straight will exhibit a force field B that is circular around it; while a coiled or looped wire exhibits a force field B that kinda comes from the middle of the loop and spreads outwards."
"The second right hand rule is used to determine the direction of the field lines in a straight current carrying wire. The third right hand rule is used to determine the direction of the field lines for a circular loop of current carrying wire."
"I understand that a magnetic B field will exert magnetic forces on a test object, while a source object (a straight section of current-carrying wire, or a closed loop of current) will create a magnetic B field everywhere around itself."
"RHR2 and RHR3 are used for the direction of the magnetic field of wires. RHR2 specifically is for straight wires and has thumb as current, palm as distance from wire to location and curl of fingers as the direction of magnetic field B. RHR3 is for circular loop of current carrying wire and the thumb = direction magnetic field B, curl = direction of current."
"The direction of magnetic force is given by the first right-hand rule (RHR1, or 'hidden dragon'), where the thumb is used either for the velocity direction of a positive charge, or for the direction of 'conventional current' (positive charge flow) along a straight section of wire."
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'm having trouble convincing myself that 'two of the sections will have forces exerted on them by the magnetic field that will result in the loop turning until it is perpendicular to the magnetic field.' When I do it, I get F pointing towards me, not down or up. I think my RHR1 is broken."
"I found the majority of this presentation confusing, specifically how to use the hand rules."
"I am still struggling with what a solenoid is. I don't know what I am supposed to be applying it to."
"hat I found confusing about the reading was completely grasping the loop-rule. I can understand how a magnetic field will circle around a given straight section of current-carrying wire in conjunction with the north and south poles of the magnet. But I just do not understand how the magnetic field will loop around a current-carrying wire at a fixed distance around a wire. Wouldn't the magnetic field circle around a wire at distance approaching infinity? even though the force might be very weak. Is the equation to determine the magnitude of a magnetic field similar to solving the magnitude of an electric field? Because I think that would clear it up for me."
"I'm pretty sure I find everything confusing. I've consistently missed lectures on circuits and things relating to this. I think I may be screwed."
"Too many things to remember!"
"Does the direction of the magnetic field for a loop of current wire go only in the direction of the thumb in RHR3?"
"honestly have no idea what is going on. I felt like I kind of understood the right hand rule in class but then when I looked at the homework I actually have no idea what's happening at all. And then don't even get me started trying to add the other two rules to that."
"I don't get magnetism."
"I didn't find any of the concepts particularly confusing. Most of the problems I encountered involve the implementation of the three right hand rules."
"How to use the R1H1 rule for the second part of the magnetism. I'm still not sure if I understand the whole R1H1 and RHR2 concept that well."
"The RHR2 and RHR3 hand gestures. And I will benefit from some explanation in class to clarify."
"I get the RHR2 and 3 because they are relatively simple, but still questioning RHR1."
State/describe the symbol used for the "permeability of free space," and give its SI units.
"'Mu nought,' µ0 = 4π×10–7 T⋅m/A."
"Henries per meter (H/m), amount of resistance encountered when forming a magnetic field."
"The symbol is the one that looks like a fancy m, pronounced as 'mew' and its units are N per A squared."
"µ0, kinda super confused."
"Greek 'm,' µ0 = henries/meter or newtons per ampere squared."
State whether it is possible or not possible for the following pairs of objects to exert magnetic forces on each other.
(Only correct responses shown.)
The ends of two bar magnets: possible [60%]
The end of a bar magnet, and a stationary charge: not possible [30%]
The end of a bar magnet, and a moving charge: possible [63%]
Current flowing through a wire, and a stationary charge: not possible [17%]
Current flowing through a wire, and a moving charge: possible [60%]
Current flowing through a wire, and another wire with current in it: possible [57%]
(Only correct responses shown.)
Current I in long straight wire: thumb [83%]
Magnetic field B: curled fingers [83%]
(Only correct responses shown.)
Current I in circular loop of wire wire: curled fingers [77%]
Magnetic field B: thumb [80%]
Explain the similarities/differences between a circular current loop, and a solenoid.
"A solenoid is basically 'an array of connected [circular] current loops.'"
"We use RHR2 for a circular current loop and then RHR3 for a solenoid."
"Circular current loop: Creates a concentrated magnetic field in the circle of the center of the loop compared to the outside of the loop. Solenoid: Controlled magnetic field similar to an inductor."
"Coil is a series of loops and solenoid is a long tightly wound loop."
"I still can't grasp what a solenoid is..."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I'm still lost on how to use my hand for the right hand rule."
"CONFUSED!"
"Why did I feel like the semester was over when we left for spring break? We only have six weeks left but they're going to be tough."
"My hand cramps doing the RHRs."
"The hand...I am lost."
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