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.
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 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.
Section 30676
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.
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 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.
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

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!)
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

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!)
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 = AZ(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.)