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Astronomy and physics education research and comments, field-tested think-pair-share (peer instruction) clicker questions, flashcard questions, in-class activities (lecture-tutorials), current events questions, backwards faded scaffolding laboratories, Hake gains, field-tested multiple-choice and essay exam questions, indices of discrimination, presentation slides, photos, ephemerae, astronomy in the marketplace, unrelated random sketches and minutiae.

20170429

Physics quiz archive: magnetism, induction

Physics 205B Quiz 6, spring semester 2017
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz06LnDr

Sections 30882, 30883 results

0- 6 :
7-12 :
13-18 :	******** [low = 15]
19-24 :	************** [mean = 21.8 +/- 4.1]
25-30 :	******* [high = 30]

Astronomy midterm question: plausible AMNH classification of Ceres and asteroids?

Astronomy 210 Midterm 2, spring semester 2017
Cuesta College, San Luis Obispo, CA

An astronomer at the American Museum of Natural History proposed an alternate scheme for defining planets and non-planets[*]:

A planet is (1) a body that has swept up or scattered most of the material from its orbit around the sun, and (2) has an orbit that can never collide with another planet. A non-planet is (1) a body that has not swept up or scattered most of the material from its orbit around the sun, and (2) has an orbit that can collide with either a planet or another non-planet.

Discuss how Ceres could be considered a planet under these new rules, but the asteroids would not. Explain your answer using these new rules, and characteristics of Ceres and of the asteroids.

[*] Steven Soter, "What is a Planet?" The Astronomical Journal, vol. 132, pp. 2513-2519 (August 16, 2006), arxiv.org/pdf/astro-ph/0608359.pdf. (As discussed in this article, however, Ceres would still not be considered a planet with this new scheme.)

Solution and grading rubric:

p:
Ceres is a dwarf planet that is rounded in shape and is much larger than the remainder of the asteroids, which are much smaller and are irregular in shape. Since Ceres is much larger, it can be argued that (1) if it "swept up most of the material from its orbit," and (2) since it can only collide with asteroids in its orbit, and thus can be considered a planet under these two rules. Since the asteroids are much smaller, it can be argued that (1) they did not sweep up most of the material from their orbits, and (2) are in orbits that can collide with each other or with Ceres, classifying them as non-planets.
r:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. At least discusses three of the four points above.
t:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Explicitly discusses the AMNH rules, but does not apply them correctly/consistently/completely, typically only Ceres or only asteroids, or only the first or second criteria to both.
v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion only tangentially related to the AMNH rules.
x:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion unrelated to the AMNH rules.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Section 30674
Exam code: midterm02nDcc
p: 13 students
r: 2 students
t: 5 students
v: 1 student
x: 0 students
y: 0 students
z: 0 students

Section 30676
Exam code: midterm02sL0w
p: 28 students
r: 7 students
t: 5 students
v: 3 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1515):

Astronomy midterm question: same absolute magnitude stars, different distances closer than 10 parsecs?

Astronomy 210 Midterm 2, spring semester 2017
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:

Pdg: Can two stars have the same absolute magnitude, if they both have different distances closer than 10 parsecs?
pub: Yes, if the nearer star has a brighter apparent magnitude (bigger negative number, or smaller positive number), and the farther star has a dimmer apparent magnitude.

Discuss whether this answer is correct or incorrect, and how you know this. Explain using the relationships between apparent magnitude, absolute magnitude, and distance.

[*] answers.yahoo.com/question/index?qid=20170305023512AAeRXO8.

Solution and grading rubric:

p:
Correct. Understands difference between apparent magnitude m (brightness as seen from Earth, when placed at their actual distance from Earth) and absolute magnitude M (brightness as seen from Earth, when placed at the "fair comparison distance" of 10 parsecs away), and discusses:
1. a star 10 parsecs away with a certain absolute magnitude will get brighter when placed closer than 10 parsecs away from Earth, and thus its apparent magnitude will be brighter than its absolute magnitude; and
2. since both stars have the same absolute magnitude at 10 parsecs, the nearer star would be located much closer than 10 parsecs, resulting in a much brighter apparent magnitude, while the farther star would be located just a little closer than 10 parsecs, resulting in only a slightly brighter apparent magnitude, dimmer than the other star.
r:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. May have one star located closer than 10 parsecs, or moving in the wrong direction to change its apparent magnitude to its absolute magnitude.
t:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of relationships between apparent magnitudes, absolute magnitudes, and distances.
v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use relationships between apparent magnitudes, absolute magnitudes, and distances.
x:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on garbled definitions of, or not based on proper relationships between apparent magnitudes, absolute magnitudes, and distances.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Section 30674
Exam code: midterm02nDcc
p: 13 students
r: 2 students
t: 2 students
v: 4 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 7697):

Another sample "p" response (from student 5150):

Astronomy midterm question: same absolute magnitude stars, different distances farther than 10 parsecs?

Astronomy 210 Midterm 2, spring semester 2017
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:

Pdg: Can two stars have the same absolute magnitude, if they both have different distances farther than 10 parsecs?
pub: Yes, if the nearer star has a brighter apparent magnitude (bigger negative number, or smaller positive number), and the farther star has a dimmer apparent magnitude.

p:
Correct. Understands difference between apparent magnitude m (brightness as seen from Earth, when placed at their actual distance from Earth) and absolute magnitude M (brightness as seen from Earth, when placed at the "fair comparison distance" of 10 parsecs away), and discusses:
1. a star at 10 parsecs away with a certain absolute magnitude will get dimmer when placed further than 10 parsecs away from Earth, and thus its apparent magnitude will be dimmer than its absolute magnitude; and
2. since both stars have the same absolute magnitude at 10 parsecs, the nearer star would be located just a little farther away from 10 parsecs, resulting in a slightly dimmer apparent magnitude, while the farther star would be located much farther away from 10 parsecs, resulting in a much dimmer apparent magnitude.
r:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. May have one star located closer than 10 parsecs, or moving in the wrong direction to change its apparent magnitude to its absolute magnitude.
t:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of relationships between apparent magnitudes, absolute magnitudes, and distances.
v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use relationships between apparent magnitudes, absolute magnitudes, and distances.
x:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on garbled definitions of, or not based on proper relationships between apparent magnitudes, absolute magnitudes, and distances.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Section 30676
Exam code: midterm02sL0w
p: 18 students
r: 6 students
t: 4 students
v: 9 students
x: 6 students
y: 0 students
z: 0 students

A sample "p" response (from student 0428):

Another sample "p" response (from student 0511):

Astronomy midterm question: example of a cooler star larger than a hotter star?

Astronomy 210 Midterm 2, spring semester 2017
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:

Pdg: What is an example of a cooler star being larger than a hotter star?
nin: The sun and a red star like Betelgeuse.

Discuss why this answer is correct, 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=20170301055021AAZuNwb.

Solution and grading rubric:

p:
Correct. Uses Wien's law to determine that the sun would be the hotter (yellow) star, while Betelgeuse would be the (red) cooler star. Then uses the Stefan-Boltzmann law and/or interprets H-R diagram to demonstrate how Betelgeuse would need to be either a red giant or a red supergiant (which it actually is) in order to be cooler and larger than the sun, a medium-mass main-sequence star.
r:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Compares two stars (hotter, smaller vs. cooler, larger), where the hotter star is more luminous than the cooler star, but does not explicitly compare the sun versus a red (giant/supergiant) star.
t:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of Wien's law, but the Stefan-Boltzmann law and/or H-R diagram discussion is garbled, with a hotter, smaller sun having the same luminosity as a cooler, larger red (giant/supergiant) star; or may have erroneously claimed that the two stars have the same temperature, but Stefan-Boltzmann law and/or H-R diagram discussion is consistent with this mistake in Wien's 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, the Stefan-Boltzmann law, and/or H-R diagram.
x:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion not clearly based on Wien's law, the Stefan-Boltzmann law, and/or H-R diagram.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Section 30674
Exam code: midterm02nDcc
p: 9 students
r: 9 students
t: 2 students
v: 1 student
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 9433):

Astronomy midterm question: example of a cooler star smaller than a hotter star?

Astronomy 210 Midterm 2, spring semester 2017
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:

Pdg: What is an example of a cooler star being smaller than a hotter star?
nin: The sun and a red star like Barnard's star.

p:
Correct. Uses Wien's law to determine that the sun would be the hotter (yellow) star, while Barnard's star would be the (red) cooler star. Then uses the Stefan-Boltzmann law and/or interprets H-R diagram to demonstrate how Barnard's star would need to be a red dwarf in order to be cooler and smaller than the sun, a medium-mass main-sequence star.
r:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Compares two stars (hotter, larger vs. cooler, smaller), where the hotter star is more luminous than the cooler star, but does not explicitly compare the sun versus a red (dwarf) star.
t:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of Wien's law, but the Stefan-Boltzmann law and/or H-R diagram discussion is garbled, with a hotter, larger sun having the same luminosity as a cooler, smaller red (dwarf) star; or may have erroneously claimed that the two stars have the same temperature, but Stefan-Boltzmann law and/or H-R diagram discussion is consistent with this mistake in Wien's 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, the Stefan-Boltzmann law, and/or H-R diagram.
x:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion not clearly based on Wien's law, the Stefan-Boltzmann law, and/or H-R diagram.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Section 30676
Exam code: midterm02sL0w
p: 22 students
r: 4 students
t: 9 students
v: 5 students
x: 3 students
y: 0 students
z: 0 students

A sample "p" response (from student 3428):

20170428

Astronomy current events question: early stages of Milky Way-like galaxies

Astronomy 210L, spring semester 2017
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!)

Tim Stephens, "Astronomers Observe Early Stages of Milky Way-like Galaxies in Distant Universe" (March 23, 2017)
mpifr-bonn.mpg.de/pressreleases/2017/4

The Atacama Large Millimeter Array (ALMA) in Chile observed early stages of Milky Way-like galaxies by measuring how their surrounding "super halo" of __________ absorbed light from their own quasars.
(A) distorted space-time.
(B) hydrogen gas.
(C) dark matter.
(D) globular clusters.
(E) antimatter.

Correct answer: (B)

Student responses
Sections 30679, 30680
(A) : 0 students
(B) : 16 students
(C) : 5 students
(D) : 8 students
(E) : 2 students

Astronomy current events question: Titan's nitrogen fizzy lakes

Preston Dyches, "Experiments Show Titan Lakes May Fizz with Nitrogen" (March 15, 2017)
mpifr-bonn.mpg.de/pressreleases/2017/4

Hydrocarbon lakes and seas of Saturn's moon Titan may bubble up nitrogen, based on:
(A) laboratory experiments.
(B) reflected infrared light.
(C) analysis of released gases.
(D) similar geysers in Siberia.
(E) computer simulations.

Correct answer: (A)

Student responses
Sections 30679, 30680
(A) : 12 students
(B) : 4 students
(C) : 11 students
(D) : 3 students
(E) : 1 student

Astronomy current events question: galaxy collision "relic" magnetic fields

Maja Kierdorf, Rainer Beck, Norbert Junkes, "Giant Magnetic Fields in the Universe" (March 22, 2017)
mpifr-bonn.mpg.de/pressreleases/2017/4

Maps of __________ left over from galaxy cluster collisions were made from observations of polarized radio waves by the Effelsberg radio telescope in Germany.
(A) antimatter.
(B) magnetic fields.
(C) gravitational waves.
(D) neutrino emissions.
(E) gamma rays.

Correct answer: (B)

Student responses
Sections 30679, 30680
(A) : 4 students
(B) : 21 students
(C) : 3 students
(D) : 0 students
(E) : 3 students

Online reading assignment: radioactive decay modes

Physics 205B, spring semester 2017
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.

"A nucleus must have just the right ratio of protons to neutrons or the atom becomes unstable."

"Nucleus, protons, neutrons, electrons...yeah I got this"

"Did not get to it"

"I understood that when there is not the correct ratios of protons to neutrons that the atom will turn a proton into a neutron or vice versa. There are a few different types of decay: alpha, beta (+), beta (–), and gamma."

"Decay occurs as a nucleus attempts to become more stable. A proper balance of protons and neutrons is necessary for stability. If balance is not maintained, protons may be transformed into neutrons (or vice versa), or proton/neutron couples can be released."

"The reason nuclei are unstable are due to the unfavorable ratio of protons to neutrons. The charges and forces protons carry are too much for the nuclei too handle if out of proportion."

"A nucleus containing more than 83 protons is unstable. If there are more neutrons than protons or the same amount then there is stability."

"Greater than 83 protons means unstable nuclei no matter how many neutrons. Having approximately the same number of protons as neutrons will make the nucleus stable."

"I have covered some of this in chemistry, so I know some of it but not well."

"The nucleus of an atom is composed of nucleons, that is, protons and neutrons. Radioactive decay occurs to lower the nucleus' energy state through a shift in the configuration/numbers of nucleons or when rays are released. There are five different types of radioactive decay: alpha, beta-positive, beta-negative, electron capture, and gamma."

"I understand the composition of an atom as well as the various types of decay because I have learned it before in my physics class. Alpha and gamma decay is very solid in my mind."

"I understand that alpha particles are decay that are equivalent to a helium atom flying off, thus changing the element overall to two less protons and two less neutrons. A beta particle or decay is where the radioactive material becomes a different element by gaining or losing a proton."BR>
"There are different ways for radioactive material to decay. I never knew protons could be emitted or change to neutrons and back"

"Nuclear instability is the result of an improper ratio of neutrons to protons in a nucleus. The nucleus will then emit several different types of particles in order to achieve a more stable state, depending on the number of each to begin with. The three types of decay are: alpha decay (He nucleus) Beta minus (n->p + e–) beta plus (p->n + e+) and gamma (decay->photon)."

"I understand that nuclei stable or unstable have a set of positive charged protons and neutrally charged neutrons and that from chemistry, the periodic table and how to read a specific element from the table. I also understand now that as a radioactive decay process occurs, a nucleus with an unstable configuration always seeks a more stable configuration."

"For all atomic nuclei, big and small, the key to stability is being able to keep the protons in the nucleus together. A nucleus containing more than 83 protons will always be unstable, no matter how many neutrons there are."

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.

"Mixing up the different kinds of decay. As in which are alpha, beta, and so on."

"On the homework problems for the half-life and exponential problems those were a tiny bit confusing because it wasn't clear to me that R₀ is the original rate of decay. So, doing those problems shed some light on that."

"he strong force. I understand how it is applied in the class notes for neutron balance, but what makes it different from electromagnetic force?"

"I don't really find it confusing, but I found it I retesting that neutrons and protons switch back and forth into each other inside a nucleus. I always thought they were the same 100% of the time."

"How the ratio of protons to neutrons effects the stability of the nucleus."

"I didn't understand either of the beta decays."

"Beta positive versus beta negative decay. I could benefit from some examples in class of that and also when the nucleus swallows an neutron."

"I do not understand how the neutrons hold the protons together in a nuclide in almost a 1:1 ratio up until 20 protons and then start having to dramatically increase the number of neutrons per proton."

"That protons can be turned into neutrons; I thought the protons were what made a particular element a particular element."

"Electron capture."

"Parts about different processes that unstable nuclei can undergo to achieve stable configurations. This material is very interesting, but a little difficult to understand in terms of how they all apply in a physics sense."

"I understand how you tell if a nucleus is stable or unstable, but could use a little help in determining what it would take to make it stable."

"Trying to identify the processes that increase or decrease or do not change protons into neutrons."

"Not much."

"Nada."

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

"The nucleon number is also the 'mass number,' and it can be found in the top left corner of each elements box on the periodic table. It is the number of protons and neutron in an atom."

"The total number of protons and electrons."

"Nucleon number is noted as 'A', neutrons = A – Z(atomic number, or the number of protons)."

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

α decay: decrease. [87%]
β– decay: increase. [65%]
β+ decay: decrease. [70%]
electron capture: decrease. [17%]
γ decay: does not change. [78%]

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

α decay: decrease. [57%]
β– decay: decrease. [83%]
β+ decay: increase. [78%]
electron capture: increase. [22%]
γ decay: does not change. [83%]

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. [70%]
β– decay: n → p. [87%]
β+ decay: p → n. [70%]
electron capture: p → n. [26%]
γ decay: no p/n conversion. [83%]

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

"Is my smoke detector giving off harmful radiation?" (Only if you crack it open.)

"What causes the emission of positrons or electrons when protons or neutrons transform into each other?" (Charge and mass must be conserved. Also a neutron is just a proton with an electron added to it. Weird, huh?)

"A neutron walked into a bar and asked, 'how much for a gin and tonic?' the bartender said, For you, no charge.'" (#rimshot)

"Wouldn't electron capture simply balance the charge of the entire atom, and not affect the nucleus?" (It might make the atom ionized, as it would lose an electron, and definitely affect the nucleus it turning a proton into a neutron.)

20170424

Online reading assignment: radioactive decay rates

"Radioactive decay is exponential."

"Honestly, not much. This whole concept is very foreign to me."

"Half-life is the time for one-half of a statistically large sample to decay. Half-life is proportional to the time constant and the decay constant."

"I totally understand how half lives work because I have learned it before in other classes like chemistry and geology. Those classes really helped with this lecture!"

"I understand half-life and radioactive decay as I have had it in math."

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

"After a molten sample solidifies, it will start anew with having radioactive atoms with no daughter atoms. Melting a sample 'resets' its solidification age."

"Radiation is hella bad for you."

"Haven't got to it yet."

"I would like more practice in obtaining the half-life given the time constant. Also, I want to know how equations look for radioactive dating or if you just count up the ratio of daughter atoms to radioactive atoms."

"What solidification age is and how was supposed to know which had an older solidification age."

"The concepts seem pretty easy to understand. Doing some problems to see how the different constants work would be great!"

"Very confused as to what is going on and am having trouble understanding activity (half-life decay) and half life equations."

"It all is pretty confusing, but it should clear up after lecture."

"Not sure yet."

"I'm good."

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

"Becquerel."

"Bq."

"I believe that it is Bq = 1 decay/second."

"A becquerel, Bq, is the unit for one disintegration per second."

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

less than. *** [3]

equal to. ************ [12]

greater than. ******** [8]

(Unsure/guessing/lost/help!) * [1]

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). [21%]
Sample with older solidification age: adioactive sample with daughter atoms. [75%]

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

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

"After a molten sample solidifies, it will start over with having radioactive atoms with no daughter atoms. Melting a sample restarts its solidification age."

"Not sure what is meant by 'solidification age.'"

"Uhh...what?"

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

"Not sure what the relationship between half-life and the time constant is." (As long as you realize they're not the same thing, but can be converted from one to the other (by a factor of ln(2)).)

"Is exponential decay just an overview and half-life is more specific?" (They're related to each other mathematically, as are the exponential decay and half-life decay equations. Both either will give you the same results computationally.)"

"I have always associated half-life with chemistry. It is interesting to explore this concept from a physics standpoint."

"Do you prefer Rockstar or Monster energy drinks?" (RockStar sugar-free tastes much better than Monster sugar-free.)

20170421

Astronomy current events question: early galaxy dark matter

Reinhard Genzel, Natascha M. Förster Schreiber, Hannelore Hämmerle, "Event Horizon Telescope Ready to Image Black Hole" (March 16, 2017)
mpg.de/11170451/early-galaxies-dark-matter

Very distant, early galaxies may have less dark matter than current galaxies, based on mapping the distribution of their stars':
(A) orbital velocities.
(B) brightness fluctuations.
(C) matter-antimatter ratios.
(D) neutrino emissions.
(E) fast radio bursts.

Correct answer: (A)

Student responses
Sections 30679, 30680
(A) : 10 students
(B) : 9 students
(C) : 8 students
(D) : 6 students
(E) : 0 students

Astronomy current events question: Event Horizon Telescope

Jonathan Amos, "Event Horizon Telescope Ready to Image Black Hole" (February 16, 2017)
bbc.com/news/science-environment-38937141

The Event Horizon Telescope is a "virtual telescope" that will combine data from many different __________ to image the gas and dust surrounding the supermassive black hole at the center of the Milky Way galaxy.
(A) radio telescopes.
(B) quantum supercomputers.
(C) underground neutrino detectors.
(D) gamma ray bursts.
(E) space telescopes.

Correct answer: (A)

Student responses
Sections 30679, 30680
(A) : 20 students
(B) : 2 students
(C) : 1 student
(D) : 1 student
(E) : 9 students

Astronomy current events question: LL Pegasi spiral gas pattern

Stuart Wolpert, "Using a Powerful Telescope, Scientists View Spiral Pattern of Gaseous Emissions around LL Pegasi and Its Companion Star" (March 16, 2017)
newsroom.ucla.edu/releases/astronomers-observe-a-dying-red-giant-stars-final-act

A 3-D map of the spiral pattern of gases surrounding the red giant and companion star in the LL Pegasi system was made from __________ observations by the Atacama Large Millimeter/submillimeter Array in Chile.
(A) radio wavelength.
(B) magnetic field.
(C) gravitational wave.
(D) neutrino emission.
(E) gamma ray.

Correct answer: (A)

Student responses
Sections 30679, 30680
(A) : 13 students
(B) : 0 students
(C) : 8 students
(D) : 4 students
(E) : 5 students

Online reading assignment: flux laws & devices

Physics 205B, spring semester 2017
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.

"The concept of magnetic flux. For any imaginary or actual area A (such as that enclosed by a wire loop) in the presence of a (uniform magnitude and direction) magnetic field B, the magnetic flux Φ_B is the product of the magnetic field magnitude B and the area A."

"The concept of Faraday's law and the relationship between electromagnetic force going through a wire loop and the magnetic flux changing while going through the loop. The magnetic flux must always be changing, and if it is constant, then the electromagnetic force is zero."

"According to Faraday's law, in order for emf to be induced, the flux has to change."

"Change in magnetic flux is necessary to induce current. Even if a magnetic field is present, it will not induce current if it remains constant."

"What I was able to understand from tonight's reading is that the magnetic flux Φ_B is the product of the magnetic field B and the area is A. The perpendicular sign '⊥' means the maximum value for the magnetic flux Φ_B."

"I think I get the basic concepts relating to how a changing magnetic flux creates an induced current, and how that is applied in the coil and transformer we saw. I also get the voltage can vary in a transformer, because the number of 'windings' in the core corresponds to number of turns, i.e. N."

"How to convert grams to newtons."

"Haven't gotten to it yet."

"Nothing really..."

"Faraday's Law. I didn't understand the concept of it."

"I'm not quite sure what's going on with Lenz's law. I don't see what's going on with the coils inducing a loop & creating a magnetic field."

"How to properly use all the symbols in each formula, because it seems like they are all over the place."

"How a coil resists change. I understand the comparison to throwing a brick, but a brick has mass that requires force to displace."

"The rotating coil generator was unclear. I think some clarification of Lenz's law would be very helpful. I can't seem to visualize what is going on in the explanations on the blog. You LOST me on the transformer part for sure. So, the more you could explain about that, the better."

"The physics of changing a transformer into a metal melter could be described a bit better in detail."

"I am confused on mostly every part of this. Very confused on magnetic flux."

"Nothing that I can think of."

"A lot of things man, a lot."

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

"Φ_B, the weber."

"An O with a capital I running through it, followed by a small B; Teslas times meters squared (T·m²), or 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 [91%]
Constant non-zero magnetic flux: no induced current in loop. [57%]
Magnetic flux increasing in strength: induced current in loop. [83%]
Magnetic flux decreasing in strength: induced current in loop. [83%]

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

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

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

Current: stepped-down (decreases). [39%]
Power: no change. [40%]

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

"It wouldn't be useful because it wouldn't change the voltage or the current at all."

"The difference in number of coils is what allows the step-down or step-up effect to occur."

"There would be a one-to-one relationship, which means that there would be no change in the induced current or voltage."

"Because they would nullify each other."

"I have no idea."

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

"Dude I still don't understand the whole hand thing."

"Help me."

"Where does the flux capacitor show up in all of this?"

"I gotta say, the example relating to the induction forge made it really click how powerful magnetic fields are. I guess it sounds silly, since its one of the most fundamental and powerful forces in the universe, but for some reason that short clip made it click."

20170420

Astronomy quiz question: stellar evolution states in star cluster

Astronomy 210 Quiz 6, spring semester 2017
Cuesta College, San Luis Obispo, CA

At right is an H-R diagram of a star cluster. The stars in the dashed box are __________ stars that have __________ their main-sequence life.
(A) massive; not yet begun.
(B) massive; already ended.
(C) low-mass; not yet begun.
(D) low-mass; already ended.

Correct answer (highlight to unhide): (B)

All stars in a star cluster are born at the same time, but undergo stellar evolution at different rates depending on their masses. The luminous stars at the top of the H-R diagram are massive stars that evolve faster than medium-mass and low mass stars, so a star cluster containing medium-mass stars that are in their main-sequence stage (and low mass stars that have not reached the main-sequence) will have massive stars that have already left the main-sequence.

Section 30674
Exam code: quiz06n4cI
(A) : 3 students
(B) : 16 students
(C) : 0 students
(D) : 1 student

Success level: 82% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.40

Astronomy quiz question: stellar evolution states in star cluster

Astronomy 210 Quiz 6, spring semester 2017
Cuesta College, San Luis Obispo, CA

At right is an H-R diagram of a star cluster. The stars in the dashed box are __________ stars that have __________ their main-sequence life.
(A) massive; not yet begun.
(B) massive; already ended.
(C) low-mass; not yet begun.
(D) low-mass; already ended.

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. The dim stars at the bottom of the H-R diagram are low-mass stars that slower faster than medium-mass and massive stars, so a star cluster containing medium-mass stars that are in their main-sequence stage (and massive stars that are leaving the main-sequence) will have low-mass stars that have not already reached the main-sequence.

Section 30676
Exam code: quiz06sJ4c
(A) : 2 students
(B) : 3 students
(C) : 32 students
(D) : 2 students

Success level: 83% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.18

Astronomy quiz archive: stellar evolution

Astronomy 210 Quiz 6, spring semester 2017
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz06n4cI

Section 30674

0- 8.0 :
8.5-16.0 :	**** [low = 13.5]
16.5-24.0 :	****
24.5-32.0 :	******** [mean = 25.8 +/- 7.6]
32.5-40.0 :	**** [high = 40.0]

Section 30676, version 1
Exam code: quiz06sJ4c

Section 30676

0- 8.0 :
8.5-16.0 :	** [low = 15.0]
16.5-24.0 :	************
24.5-32.0 :	**************** [mean = 26.1 +/- 5.9]
32.5-40.0 :	********* [high = 36.5]

20170419

Online reading assignment: the Milky Way (SLO campus)

Astronomy 210, spring semester 2017
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.

"The Milky Way is a beautiful galaxy, to understand how stars grow and die, and in the consuming of other smaller galaxies create more stars, is very fascinating."

"I liked the comparison of the lights at eye level in the mirrored room with the flat disk shape of the Milky Way."

"How so many of the stars in our galaxy aren't visible to us."

"William and Caroline Herschel mapping our galaxy in 1785--it gives us an idea of the progression of the astronomical science."

"I really liked how you said that even though we do not know what dark matter is made of it, it doesn't mean that it doesn't exist. and then compared it to the Zodiac killer. Very cool!"

"I liked the part on dark matter because there was something oddly comforting about it. It's like being surrounded by an invisible blanket; we're pretty sure it's there all around us but we can't prove that it's true."

"I found self-sustaining star formation cool; how the death of stars can lead to the birth of new stars and how this process repeats over and over again."

"I found it very interesting that the arms and spurs of galaxies are maintained by either fusing with a dwarf spiral galaxy or by the explosions of type II supernovae massive stars which adds to the growth and repair of a galaxies spiral arms. I thought this was interesting as I never thought of it as something that would be necessary for a galaxy to need to do."

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

"I didn't understand how the Milky Way's flat disk shape works out to be seen as just a strip of stars."

"How Shapley could estimate the distances of globular clusters. Don't understand how he calculated true luminosities of Cepheid variable stars."

"I am still a little confused on how you can map the Milky Way and how we know what it looks like, when we can't see much of it from Earth."

"The positioning of the global clusters and how we receive the information that tells us the location of the Milky Way center."

"What the rotation curve is and what it means."

"Dark matter is confusing, 'cause liiiiiike... what is it?"

"Dark matter, because how exactly can you find the dark matter?"

"The dark matter was kind of confusing to me. I don't understand how there's just a weird thing on the outside that causes gravity to spread. Its also confusing about how we have learned so much about the galaxy but some of it is just assumptions because we cannot see much due to the gas and dust."

"Why are spurs a separate thing? They look like arms but they have a different category. Is it due to size, composition, etc? I'm interested to know why they have a name besides arms."

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

As much as can be seen with the naked eye. *************** [15]

Not very much. ********** [10]

Barely seen it. ***** [5]

(Never been able to see it.) * [1]

(Unsure/guessing/lost/help!) * [1]

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%. ****** [6]

5%. ** [2]

10%. ********* [9]

50%. *** [3]

100%. ** [2]

(Unsure/guessing/lost/help!) ********** [10]

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?

"Do I have my mobile phone? If so, I'd whip out that selfie cam. Even if it was dead I could use the reflection of the screen."

"Find a puddle of water and use that as your mirror. This works very well actually, trust me I know."

"Funny, I am going to Coachella this weekend, and I was laughing because I have never packed a mirror before while camping. But this weekend, YES, no bad hair at Coachella."

"Shave your head."

"Ask a squirrel or lizard what they think."

"Put on a ball cap and call it a day! No need to look in a mirror while you're camping."

"Run my fingers through my hair to see if my hair is different from normal."

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

"Images are sent to the wheels using WiFi, and the wheel has a microprocessor and wireless adapter to interpret the signal and display it using the LED lights."

"Persistence of vision illusion from rapidly blinking lights coordinated to create patterns when swept across our field of vision."

"By spinning fast the display an image what would be un seen while standing still."

"Lights blink rapidly in a coordinated pattern."

"They use a strip of different colored lights in the wheel. So then, when the wheel is spinning, it looks like the entire wheel is one massive blob of color."

"The human brain can only process visual stimuli so quickly, so a sequence of lights blurs into a word."

"Okay, I have a bit of a hard time with this. But its something to do with the flashing patterns."

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

"The subject matter in this class just gets more interesting and more mind boggling every time."

"It's interesting and cool to see how all the different astronomers work together, even if they don't live at the same time. They appreciate each other's work and continue it when they die. If astronomers didn't work together like this, we wouldn't know half of what we know now about space and stars and galaxies." (Kind of like self-sustaining star formation?)

"The Milky Way is beautiful and fascinating. It's one of my favorite things to look up at while I'm stargazing." (Me, too.)

"The puddle thing works really well too if you want to do your makeup. You know, just in case Mrs. P-dog wants to do her makeup while in the wilderness. #protip" (Or Mrs. P-dog could find a mysterious time portal in the middle of the desert.)

"Every time you post a link on these assignments, I cannot help but to click on it, and then immediately hit the back button, but it's too late; I have to redo the assignment." (Ctrl-click or mouse-right-click on the link to open a new tab/window, without affecting the reading assignment window. #protip)

"Do you consider staying in an RV camping?" (No, but what about if you built your own "RV" yourself?)

"P-dog, is this camping question like the house party? Why are there reocurring events we aren't actually having?" (I think you need to get out more.)

20170418

Online reading assignment: the Milky Way (NC campus)

"That stars change in various ways throughout time and many variable stars pulsate like beating hearts."

"Dark matter--it's a cool way to explain how objects in the Milky Way behave, even though we have little idea what dark matter is made of."

"That our sun has traveled around our galaxy plenty of times. crazy to think that the sun revolves around the galaxy."

"The shape of the Milky Way galaxy, as I never really thought of being anything other than just a stream of stars."

"Dark matter is quite interesting. It's especially fascinating since we don't really know what it's made of."

"It was interesting to learn about spiral arms in comparison of a starfish of a Milky Way and how they are not fixed structures but they keep 'growing back.'"

"How there are spiral arms and also spurs in the Milky Way. I thought it was just made up of multiple arms, not spurs or much else really."

"The Milky Way--I wish I could see it in real life instead of just in pictures. Although it also made me hungry. Curse the people that thought it would be a good idea to name chocolate bars after astronomy references. Now all of us astronomy students can't catch a break. "

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

"How stars stop pulsating when they evolve out of the instability strip."

"The way the galaxy's spiral arm stars light up then get dark, and how dark matter works."

"There was nothing confusing about these presentations. Everything was pretty straightforward."

"I honestly didn't get the whole concept of globular cluster. I get that our galaxy has them but I don't know how to spot one."

"It will always confuse me that there is no end to space and how there are more and more galaxies outside of the Milky Way."

"I found the gravity and orbits part of the slides in your blog to be a little confusing. I don't understand the difference between 'centered' and 'spread-out' gravity."

"Why is this always the hardest part to fill out?"

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. ***** [5]

Not very much. ****** [6]

Barely seen it. *** [3]

(Never been able to see it.) *** [3]

(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%. ***** [5]

5%. ** [2]

10%. ********** [10]

50%. [0]

100%. [0]

(Unsure/guessing/lost/help!) [0]

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?

"I wouldn't care what condition my hair is in."

"I never have bad hair days. Just planned crazy hair days."

"You could ask your friend if your hair looks like a galaxy with spiral arms or an unremarkable blob-shaped galaxy."

"Look in the body of water around you or a pot or pan you have for cooking."

"Assuming my vehicle is there and for the sake of the question there are no mirrors on the car, I'd use the reflection off a window. Even if I had my phone but it was dead I could use the screen as a mirror to check."

"See if any of the other campers run away screaming, "Monster!" or "Cool! That bear has an afro!""

"Feel my hair, see if it's tangled, or poofy from humidity."

"I would look at my own shadow. I always have a bad hair day so wouldn't be surprised."

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

"It flashes lights at intervals that we perceive at images as it moves, due to the speed we process optical stimulae."

"They use a computer to program LED bars to light up and create certain images as they spin."

"Parts of the rims light up at certain points, making it look as if there is one stationary object when it is just a moving circle of blinking lights."

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

"When are we ever going to use the telescopes at night?" (Hopefully this week, weather permitting, and allowing time for the ground to dry out from the rain. I'll give you a heads-up on this on Thursday.)

"Do you have bad hair days?" (I accept the fact that bad hair days are better than having no hair at all. Still, that's what baseball caps are for.)

"Do you have MonkeyLectric Rims for your bike?" (Yes.)

"Is this Milky Way stuff going to be on the next midterm?" (No, the second midterm covers only up to stellar evolution. The midterm study guide has already been posted online.)

"Are we going to have a movie day in class and watch Zodiac?" (Nah, instead we'll use the "free day" next week to review for the midterm, and for an extra-credit group worksheet.)

"If it is speculated that there is a supermassive black hole at the center of most galaxies, how could gravity be spread out so evenly throughout the galaxy?" (Actually this is how we know that the "evenly spread out gravity" in galaxies cannot come from the central supermassive black hole, but instead from "evenly spread out" dark matter.)

"If the vast amount of matter in the Milky Way is 'dark matter,' is there dark matter in our solar system and near Earth?" (Astronomers are already looking for evidence of that right now.)

"Please go over and explain these presentations and reading from the textbook a little more extensively this week."

less than.	*** [3]
equal to.	************ [12]
greater than.	******** [8]
(Unsure/guessing/lost/help!)	* [1]

As much as can be seen with the naked eye.	*************** [15]
Not very much.	********** [10]
Barely seen it.	***** [5]
(Never been able to see it.)	* [1]
(Unsure/guessing/lost/help!)	* [1]

1%.	****** [6]
5%.	** [2]
10%.	********* [9]
50%.	*** [3]
100%.	** [2]
(Unsure/guessing/lost/help!)	********** [10]