"G = 6.67(10^11)" by AnonymousSpring Semester 2008
Cuesta College, San Luis Obispo, CA
Latest scribbling on the lift-and-erase slate in the hallway, outside the office door.
20080430
Erasing slate: universal gravitational constant
"G = 6.67(10^11)" by AnonymousSpring Semester 2008
Cuesta College, San Luis Obispo, CA
Latest scribbling on the lift-and-erase slate in the hallway, outside the office door.
Astronomy midterm question: star cluster age
Astronomy 10 Midterm 3, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q9.5
[15 points.] In cluster 1, the main sequence extends from spectral class O to spectral class K. In cluster 2, there are no main sequence stars cooler than spectral class F. Determine which star cluster is older, and explain the reasoning behind your choice.
Solution and grading rubric:
Section 4160
p: 5 students
r: 9 students
t: 10 students
v: 14 students
x: 1 student
y: 1 student
z: 0 students
A sample "p" response (from student 1223):
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q9.5
[15 points.] In cluster 1, the main sequence extends from spectral class O to spectral class K. In cluster 2, there are no main sequence stars cooler than spectral class F. Determine which star cluster is older, and explain the reasoning behind your choice.
Solution and grading rubric:
- p = 15/15:
Correct. The OBAFGKM main sequence runs from massive to medium to low-mass. Massive stars become main sequence stars sooner, and spend less time as main sequence stars than medium mass stars. Since cluster 1 (OBAFGK) has more medium-mass stars on the main sequence than cluster 2 (OBAF), then cluster 1 must be older, as more time was required for its spectral class G and K stars to reach its main sequence. - r = 12/15:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Recognizes the relationship between mass (inferred from spectral type -> temperature -> luminosity -> mass along the main sequence line), and main sequence lifetime, but rest of discussion is garbled or incomplete. - t = 9/15:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least mentions some understanding of the relationships between mass and evolution times. - v = 6/15:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. - x = 3/15:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1.5/15:
Irrelevant discussion/effectively blank. - z = 0/15:
Blank.
Section 4160
p: 5 students
r: 9 students
t: 10 students
v: 14 students
x: 1 student
y: 1 student
z: 0 students
A sample "p" response (from student 1223):
Astronomy midterm question: cool star brighter than a hot star?
Astronomy 10 Midterm 3, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q8.5
[15 points.] How is it possible that a cool star can be more luminous than a hot star? Using an H-R diagram, explain your reasoning with Wien's law and/or the Stefan-Boltzmann law
Solution and grading rubric:
Section 4160
p: 19 students
r: 10 students
t: 7 students
v: 4 students
x: 0 students
y: 0 students
z: 0 students
A sample "p" response (from student 1231):
Another "p" response (from student 4607), using what appears to be a luminosity versus wavelength graph (due to the Planck curves) rather than a luminosity versus temperature (H-R digram) graph:
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q8.5
[15 points.] How is it possible that a cool star can be more luminous than a hot star? Using an H-R diagram, explain your reasoning with Wien's law and/or the Stefan-Boltzmann law
Solution and grading rubric:
- p = 15/15:
Correct. The Stefan-Boltzmann law states that luminosity depends on both the size (surface area) of the star, and its temperature. Thus a merely warm star can still be more luminous than a hotter star if the warm star is much bigger in size than the hotter star. - r = 12/15:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Stefan-Boltzmann law is garbled, but at least understands how size can be independent from temperature in determining the luminosity of a star. - t = 9/15:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Discussion based somehow on Wien's law and/or the Stefan-Boltzmann law. - v = 6/15:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Typically confuses luminosity with apparent magnitude by saying that the warm star could be closer to the Earth than the hotter star, when in fact luminosity (and absolute magnitude) are unaffected by distance. - x = 3/15:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1.5/15:
Irrelevant discussion/effectively blank. - z = 0/15:
Blank.
Section 4160
p: 19 students
r: 10 students
t: 7 students
v: 4 students
x: 0 students
y: 0 students
z: 0 students
A sample "p" response (from student 1231):
Another "p" response (from student 4607), using what appears to be a luminosity versus wavelength graph (due to the Planck curves) rather than a luminosity versus temperature (H-R digram) graph:
20080429
Astronomy midterm question: Sun as a pulsar?
Astronomy 10 Midterm 3, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal M3.5
[15 points.] Decide whether our Sun will ever become a pulsar. If so, then discuss how this process will occur. If not, then discuss why this process cannot occur. Explain using the properties and evolution of stars.
Solution and grading rubric:
Section 4160
p: 9 students
r: 3 students
t: 10 students
v: 9 students
x: 7 students
y: 1 student
z: 1 student
Section 5166
p: 11 students
r: 5 students
t: 14 students
v: 22 students
x: 3 students
y: 0 students
z: 0 students
A sample "p" response (from student 0223):
Another "p" response (from student 4607), perhaps looking to be disappointed when the Sun does not go out with a bang:
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal M3.5
[15 points.] Decide whether our Sun will ever become a pulsar. If so, then discuss how this process will occur. If not, then discuss why this process cannot occur. Explain using the properties and evolution of stars.
Solution and grading rubric:
- p = 15/15:
Correct. Adequately describes either what the Sun would eventually become (white dwarf), or why the Sun cannot become a neutron star (pulsar). - r = 12/15:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. - t = 9/15:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least demonstrates understanding that the Sun is not massive enough to become a supergiant -> type II supernova -> neutron star, and/or understands the properties of a pulsar that presumably cannot be attained by the medium-mass Sun. - v = 6/15:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Explains that the Sun will become a pulsar, or explains that the Sun cannot become a pulsar because it is too massive. - x = 3/15:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1.5/15:
Irrelevant discussion/effectively blank. - z = 0/15:
Blank.
Section 4160
p: 9 students
r: 3 students
t: 10 students
v: 9 students
x: 7 students
y: 1 student
z: 1 student
Section 5166
p: 11 students
r: 5 students
t: 14 students
v: 22 students
x: 3 students
y: 0 students
z: 0 students
A sample "p" response (from student 0223):
Another "p" response (from student 4607), perhaps looking to be disappointed when the Sun does not go out with a bang:
20080428
Astronomy midterm question: H-R turnoff points
Astronomy 10 Midterm 3, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q9.5
[15 points.] Show what the turnoff point of a star cluster is on an H-R diagram, and explain how this can be used to estimate the age of the stars in the cluster.
Solution and grading rubric:
Section 5166
p: 9 students
r: 4 students
t: 15 students
v: 10 students
x: 7 students
y: 7 students
z: 3 students
A sample "p" response (from student 9518):
A sample "y" response (froms student ), who like many others felt compelled to write something down (for minimal partial credit) rather than leave the answer blank:
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q9.5
[15 points.] Show what the turnoff point of a star cluster is on an H-R diagram, and explain how this can be used to estimate the age of the stars in the cluster.
Solution and grading rubric:
- p = 15/15:
Correct. "Turnoff point" is where stars from a cluster deviate from the main-sequence line. A turnoff point near the top left indicates a young cluster, as the massive stars have not yet reached their supergiant phases, turnoff point near the bottom right indicates an older cluster, as only the low-mass stars are still on the main sequence. Clearly indicates/draw/describes what a typical turnoff point looks like, and how its position is correlated with age. May instead describe how the different evolution tracks/rates of different mass stars that are observed on the main sequence line can be used to determine the age of a star cluster, without explicit mention of the "turnoff point." - r = 12/15:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. - t = 9/15:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least understands mass determines evolution tracks/rates. - v = 6/15:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. - x = 3/15:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1.5/15:
Irrelevant discussion/effectively blank. - z = 0/15:
Blank.
Section 5166
p: 9 students
r: 4 students
t: 15 students
v: 10 students
x: 7 students
y: 7 students
z: 3 students
A sample "p" response (from student 9518):
A sample "y" response (froms student ), who like many others felt compelled to write something down (for minimal partial credit) rather than leave the answer blank:
20080427
Astronomy midterm question: cooler, brighter star versus dimmer, hotter star
Astronomy 10 Midterm 3, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q8.5
[15 points.] How is it possible that a more luminous star can be cooler than a less luminous star? Using an H-R diagram, explain your reasoning with Wien's law and/or the Stefan-Boltzmann law.
Solution and grading rubric:
Section 5166
p: 21 students
r: 10 students
t: 9 students
v: 11 students
x: 2 students
y: 1 student
z: 1 student
A sample "p" response (from student 1315):
This same student, like many others, made a thumbnail note of Wien's law and the Stefan-Boltzmann law on their exam paper at the start of the midterm. Note the explicit use of the word "proportional" instead of the symbol, which some students this semester called "The Pliers."
Another student 1652, after writing a "p" response, decried the abstractness and irrelevance of astronomy at this point in the semester.
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal Q8.5
[15 points.] How is it possible that a more luminous star can be cooler than a less luminous star? Using an H-R diagram, explain your reasoning with Wien's law and/or the Stefan-Boltzmann law.
Solution and grading rubric:
- p = 15/15:
Correct. The Stefan-Boltzmann law states that luminosity depends on both the size (surface area) of the star, and its temperature. Thus a cooler star can still be more luminous than a hotter star if the cooler star is much bigger in size than the hotter star. - r = 12/15:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Stefan-Boltzmann law is garbled, but at least understands how size can be independent from temperature in determining the luminosity of a star. May confound mass with size in discussion. - t = 9/15:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Discussion based somehow on Wien's law and/or the Stefan-Boltzmann law. - v = 6/15:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Typically confuses luminosity with apparent magnitude by saying that the cooler star could be closer to the Earth than the hotter star, when in fact luminosity (and absolute magnitude) are unaffected by distance. - x = 3/15:
Implementation/application of ideas, but credit given for effort rather than merit. - y = 1.5/15:
Irrelevant discussion/effectively blank. - z = 0/15:
Blank.
Section 5166
p: 21 students
r: 10 students
t: 9 students
v: 11 students
x: 2 students
y: 1 student
z: 1 student
A sample "p" response (from student 1315):
This same student, like many others, made a thumbnail note of Wien's law and the Stefan-Boltzmann law on their exam paper at the start of the midterm. Note the explicit use of the word "proportional" instead of the symbol, which some students this semester called "The Pliers."
Another student 1652, after writing a "p" response, decried the abstractness and irrelevance of astronomy at this point in the semester.
20080426
Education research: "guessing/don't know" clicker response
Comment was made on the previous post: Astronomy clicker question: type II supernova energy source.
Though not an option on this semester's (Spring 2008) Astronomy 10 clicker questions, there is an "I'm lost, and I don't know how to answer this" response on Physics 5A clicker questions (cf. previous post, Physics clicker question: average versus instantaneous velocity for an example), which is a much more common response by students earlier in the semester, than later in the semester, most likely due to an unfamiliarity with both clickers and the material in general. (Whenever the "I'm lost" category does become the majority of responses in sporadic cases, then yes, the instructor is obliged to diagnose the cause of the disconnect, and recover using more exposition/examples.)
Also for some clicker questions in Physics 5A, students enter a numerical value for their answer following a calculation. If students are lost and don't know how to answer the question, they are instructed to enter a "nonsense" numerical answer (e.g., "-999") rather than an approximate guess. These answers will then fall outside the correct answer (which can be extended to within a +/- uncertainty), and also amuses the class as to the creativity of "wild" answers.
Thank you for providing such an extraordinary resource through your blog of questions, etc!
Question: Do you or other professors ever use (or have you considered using) a response of "? - I don't want to guess."
I used this response frequently for formative assessment questions when I taught math at the college level and integrated the use of clickers in my teaching. Students were quite willing to choose this response because they weren't embarrassed after choosing it.
By providing this response for questions used in formative assessment I was able to get better data to inform my instruction. Sometimes (much to my chagrin) 30-50% of my students would choose this response following instruction on a topic so that I then knew I should reteach the topic and then reassess.
Your thoughts on this?
Thanks.
Tim Fahlberg
Though not an option on this semester's (Spring 2008) Astronomy 10 clicker questions, there is an "I'm lost, and I don't know how to answer this" response on Physics 5A clicker questions (cf. previous post, Physics clicker question: average versus instantaneous velocity for an example), which is a much more common response by students earlier in the semester, than later in the semester, most likely due to an unfamiliarity with both clickers and the material in general. (Whenever the "I'm lost" category does become the majority of responses in sporadic cases, then yes, the instructor is obliged to diagnose the cause of the disconnect, and recover using more exposition/examples.)
Also for some clicker questions in Physics 5A, students enter a numerical value for their answer following a calculation. If students are lost and don't know how to answer the question, they are instructed to enter a "nonsense" numerical answer (e.g., "-999") rather than an approximate guess. These answers will then fall outside the correct answer (which can be extended to within a +/- uncertainty), and also amuses the class as to the creativity of "wild" answers.
20080425
Astronomy clicker question: type II supernova energy source
Astronomy 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal M3.4
Students were asked the following clicker question (Classroom Performance System, einstruction.com) in the middle of their learning cycle:
[0.3 points.] A supergiant will eventually explode as a type II supernova. What provides the energy for this explosion?
(A) Radioactive decays of unstable heavy elements.
(B) Fusion of light elements into heavy elements.
(C) Sudden gravitational contraction.
(D) Dark energy.
Correct answer: (C)
Student responses
Section 4160
(A) : 5 students
(B) : 9 students
(C) : 13 students
(D) : 3 students
Section 5166
(A) : 7 students
(B) : 16 students
(C) : 25 students
(D) : 6 students
Response (D) is merely a ruse (as it had not yet been covered yet in this course sequence). Response (A) is fission, which is not a source of energy for a star. Response (D) is fusion, which can no longer provide energy for a star at the end of its supergiant phase, as it core is iron at this point, past which requires more energy to be put in than can be released by fusion. Thus with no energy source to balance gravity, the core undergoes runaway contraction (becoming a neutron star in the process), and the resulting energy from this gravitational collapse of the core is transferred to the outer layers of the supergiant in an "implosion-explosion" sequence--a type II supernova.
Previous post: Type II supernova simulators.
Cuesta College, San Luis Obispo, CA
Astronomy 10 learning goal M3.4
Students were asked the following clicker question (Classroom Performance System, einstruction.com) in the middle of their learning cycle:
[0.3 points.] A supergiant will eventually explode as a type II supernova. What provides the energy for this explosion?
(A) Radioactive decays of unstable heavy elements.
(B) Fusion of light elements into heavy elements.
(C) Sudden gravitational contraction.
(D) Dark energy.
Correct answer: (C)
Student responses
Section 4160
(A) : 5 students
(B) : 9 students
(C) : 13 students
(D) : 3 students
Section 5166
(A) : 7 students
(B) : 16 students
(C) : 25 students
(D) : 6 students
Response (D) is merely a ruse (as it had not yet been covered yet in this course sequence). Response (A) is fission, which is not a source of energy for a star. Response (D) is fusion, which can no longer provide energy for a star at the end of its supergiant phase, as it core is iron at this point, past which requires more energy to be put in than can be released by fusion. Thus with no energy source to balance gravity, the core undergoes runaway contraction (becoming a neutron star in the process), and the resulting energy from this gravitational collapse of the core is transferred to the outer layers of the supergiant in an "implosion-explosion" sequence--a type II supernova.
Previous post: Type II supernova simulators.
Erasing slate: Elmo, presumably
"Untitled" by AnonymousSpring Semester 2008
Cuesta College, San Luis Obispo, CA
Latest scribbling on the lift-and-erase slate in the hallway, outside the office door.
20080424
Physics quiz question: constant cross-section pipe flow
Physics 5A Quiz 5, Spring Semester 2008
Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 9.51
[Version 1]
[3.0 points.] Water flows through a pipe with a speed of 0.80 m/s through a pipe of 2.0 cm inside radius, at point [1]. The pipe has the same radius of 2.0 cm, at point [2], at a height lower than point [1]. How does the speed of the water change it flows from [1] to [2]?
(A) Speed increases.
(B) Speed remains the same.
(C) Speed decreases.
(D) (Not enough information is given to determine this.)
Correct answer: (B)
From the continuity equation, if the pipe maintains a constant cross-sectional area, then the speed does not change as it flows from point [1] to point [2]. (However, in this case since the height drops, such that according to Bernoulli's equation there is a pressure increase for the water as it flows from point [1] to point [2].) Students apparently were inclined to say that water automatically increases speed as it flows "downhill" (but in this case, water is confined to within a pipe, and must obey continuity), or that perhaps viscosity (not covered in this course) is a factor in slowing down the fluid.
Student responses
Sections 4987, 4988
(A) : 9 students
(B) : 8 students
(C) : 2 students
(D) : 0 students
[Version 2]
[3.0 points.] Water flows through a pipe with a speed of 0.80 m/s through a pipe of 2.0 cm inside radius, at point [1]. The pipe has the same radius of 2.0 cm, at point [2], at a height higher than point [1]. How does the speed of the water change it flows from [1] to [2]?
(A) Speed increases.
(B) Speed remains the same.
(C) Speed decreases.
(D) (Not enough information is given to determine this.)
Correct answer: (B)
From the continuity equation, if the pipe maintains a constant cross-sectional area, then the speed does not change as it flows from point [1] to point [2]. (However, in this case since the height increases, such that according to Bernoulli's equation there is a pressure decrease for the water as it flows from point [1] to point [2].) Students apparently were inclined to say that water automatically decreases speed as it flows "uphill" (but in this case, water is confined to within a pipe, and must obey continuity), or that perhaps viscosity (not covered in this course) is a factor in slowing down the fluid.
Student responses
Sections 4987, 4988
(A) : 1 student
(B) : 8 students
(C) : 7 students
(D) : 0 students
Previous post: Physics quiz question: ideal laminar flow through horizontal pipe.
Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 9.51
[Version 1]
[3.0 points.] Water flows through a pipe with a speed of 0.80 m/s through a pipe of 2.0 cm inside radius, at point [1]. The pipe has the same radius of 2.0 cm, at point [2], at a height lower than point [1]. How does the speed of the water change it flows from [1] to [2]? (A) Speed increases.
(B) Speed remains the same.
(C) Speed decreases.
(D) (Not enough information is given to determine this.)
Correct answer: (B)
From the continuity equation, if the pipe maintains a constant cross-sectional area, then the speed does not change as it flows from point [1] to point [2]. (However, in this case since the height drops, such that according to Bernoulli's equation there is a pressure increase for the water as it flows from point [1] to point [2].) Students apparently were inclined to say that water automatically increases speed as it flows "downhill" (but in this case, water is confined to within a pipe, and must obey continuity), or that perhaps viscosity (not covered in this course) is a factor in slowing down the fluid.
Student responses
Sections 4987, 4988
(A) : 9 students
(B) : 8 students
(C) : 2 students
(D) : 0 students
[Version 2]
[3.0 points.] Water flows through a pipe with a speed of 0.80 m/s through a pipe of 2.0 cm inside radius, at point [1]. The pipe has the same radius of 2.0 cm, at point [2], at a height higher than point [1]. How does the speed of the water change it flows from [1] to [2]? (A) Speed increases.
(B) Speed remains the same.
(C) Speed decreases.
(D) (Not enough information is given to determine this.)
Correct answer: (B)
From the continuity equation, if the pipe maintains a constant cross-sectional area, then the speed does not change as it flows from point [1] to point [2]. (However, in this case since the height increases, such that according to Bernoulli's equation there is a pressure decrease for the water as it flows from point [1] to point [2].) Students apparently were inclined to say that water automatically decreases speed as it flows "uphill" (but in this case, water is confined to within a pipe, and must obey continuity), or that perhaps viscosity (not covered in this course) is a factor in slowing down the fluid.
Student responses
Sections 4987, 4988
(A) : 1 student
(B) : 8 students
(C) : 7 students
(D) : 0 students
Previous post: Physics quiz question: ideal laminar flow through horizontal pipe.
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