Astronomy final exam question: Mars' past history

Astronomy 210 Final Exam, fall semester 2012
Cuesta College, San Luis Obispo, CA

An article on an online science and science fiction discussion blog(*) discusses the past history and possibility of future colonization of Mars:

So, what happened on Mars? When volcanic activity halted on Mars...this once warm and inviting place, with enough atmospheric pressure and a high enough temperature to support liquid water, become a frozen rock with [a thin] atmosphere...

Discuss how the end of volcanic activity on Mars caused temperatures to drop and its atmosphere to become thinner. Explain using the properties of greenhouse gases and geological activity.

(*)Jason Shankel, "How We Will Terraform Mars," December 19, 2011, io9.com/5868115/how-we-will-terraform-mars.

Solution and grading rubric:

• p:
  Correct. Discusses features of the "runaway refrigerator" model of Mars' past: (a) Mars' small mass would make it unable to retain its atmosphere due to its slower escape velocity, (such that its atmosphere thins), and thus (b) unable to retain enough heat (such that its temperatures will drop). May also have discussed how Mars' oceans removed greenhouse gases from the atmosphere.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. One of two points (a)-(b) correct, other is problematic/incomplete.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Both points (a)-(b) problematic/incomplete, or one point correct while other is missing.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least understands factors that contribute to atmosphere retention and greenhouse effect.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discusses factors other than relevant to atmosphere retention and greenhouse effect.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 70158
Exam code: finalSor3
p: 7 students
r: 9 students
t: 9 students
v: 3 students
x: 1 student
y: 0 students
z: 0 students

Section 70160
Exam code: finalNon0
p: 6 students
r: 9 students
t: 8 students
v: 4 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 2192):

Physics final exam question: average speed greater than average velocity magnitude?

Physics 205A Final Exam, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Questions 2.1, 2.2, 3.9

A Physics 205A student kicks a ball off the edge of a cliff with an initial velocity that is directed 45° below the horizontal, and the ball hits the ground below 3.0 s later. Discuss why the average speed of the ball will be greater than the magnitude of the average velocity as it falls to the ground. Explain your reasoning using the properties of distance traveled, displacement, and elapsed time.

Solution and grading rubric:

• p:
  Correct. Understands distinction between average speed (distance traveled divided by elapsed time) and magnitude of average velocity (magnitude of displacement divided by elapsed time), and clearly indicates how the distance traveled by the ball is greater than the magnitude of displacement during its trajectory towards the ground.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Does not explicitly discuss how distance traveled is greater than the magnitude of displacement for this trajectory (as most generally it is possible for the distance traveled to be equal to the magnitude of the displacement).
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete. At least distinguishes between distance traveled and magnitude of displacement.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion based on some other aspect of kinematics, vectors, and differential calculus.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on concepts other than kinematics, vectors, and differential calculus.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 70854, 70855
Exam code: finalPr0p
p: 20 students
r: 8 students
t: 11 students
v: 11 students
x: 0 students
y: 0 students
z: 1 student

A sample "p" response (from student 3003):

Physics final exam question: strings with same frequencies, different harmonics

Physics 205A Final Exam, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problems 11.9, 11.54, Review Exercise 14, p. 454

A string has its tension set by a hanging mass M, and resonates at its fundamental frequency at 150 Hz. This same string will resonate with two antinodes at 150 Hz when a different mass m is hanging from it. Discuss why M > m. Explain your reasoning using the properties of wave speeds, periodic waves, and standing waves.

Solution and grading rubric:

• p:
  Correct. Understands how (a) the fundamental frequency is proportional to wave velocity, and (b) the wave velocity depends on the square root of the mass creating the tension, and (c) the string vibrating at its second harmonic has a fundamental frequency half that of the other string, such that the second harmonic vibrating string has a slower wave velocity, a lower tension, and thus a smaller hanging mass.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least understands how the hanging mass affects tension, and thus wave velocity.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 70854, 70855
Exam code: finalPr0p
p: 18 students
r: 6 students
t: 17 students
v: 9 students
x: 0 students
y: 0 students
z: 1 student

A sample "p" response (from student 2121):
Another sample "p" response (from student 9494):

Physics final exam question: thermal expansion of different length bars

Physics 205A Final Exam, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Comprehensive Problem 13.101, Problem 14.11

A 0.50 m long steel bar has same cross-sectional area as a 1.00 m long steel bar, and are both initially at room temperature (25° C). The same amount of heat is evenly applied to each bar. Discuss why both bars would expand by 0.0001 m from their original lengths. (Ignore heat lost to the environment.) Explain your answer using the properties of heat, internal energy, temperature, and thermal expansion.

Solution and grading rubric:

• p:
  Correct. Same heat is applied to each bar, but:
  1. the shorter bar is half the mass of the longer bar, such that the increase in temperature of the shorter bar will be twice that of the longer bar.
  2. the shorter bar has half the length, but twice the temperature change compared to the longer bar, and so the length expansion (which is proportional to both the original length and temperature increase) will be the same compared to the longer bar.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. At least recognizes that (1) bars experience different temperature changes, and (2) expansion of bars depends on both original length and temperature change.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. May instead argue that same cross-sectional area is relevant factor, or same temperature change for both bars, etc. At least some discussion based on thermal expansion and/or heat capacity.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on phenomena other than thermal expansion or heat capacity.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 70854, 70855
Exam code: finalPr0p
p: 9 students
r: 7 students
t: 5 students
v: 25 students
x: 0 students
y: 3 students
z: 2 students

A sample "p" response (from student 1408), starting off with a few black fuzzy caterpillars:

Physics final exam question: heat conduction comparison

Physics 205A Final Exam, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Example 14.10, Practice Problem 14.10

A 0.50 m long steel bar has twice the cross-sectional area as a 1.00 m long steel bar. The bottom of each bar is immersed in 20° C water, while the top of each bar is heated to 80° C. (Ignore the very slight thermal expansion of these bars). Discuss why the 0.50 m bar will conduct more heat per time than the 1.00 m bar. Explain your answer using the properties of heat, temperature, and heat transfer.

Solution and grading rubric:

• p:
  Correct. Heat is conducted from the top to the bottom of each bar, at a rate (1) proportional to the cross-sectional area, and (2) inversely proportional to the length, such that the wider, shorter bar will conduct heat at a rate four times faster than the narrower, longer bar.
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Typically argues only (1) area, or only (2) length as a factor in why the wider, shorter bar will conduct heat faster than the narrower, longer bar.
• t:
  Nearly correct, but argument has conceptual errors, or is incomplete.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least recognizes different factors (1)-(2) and attempts to discuss heat conduction along the length of the bars.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on phenomena other than heat conduction along the length of the bars.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 70854, 70855
Exam code: finalPr0p
p: 16 students
r: 18 students
t: 4 students
v: 9 students
x: 1 student
y: 1 student
z: 2 students

A sample "p" response (from student 1337):
Another sample "p" response (from student 1391), explicitly discussing thermal resistance:
A sample "r" response (from student 4568), only discussing the difference in cross-sectional area:

Physics final exam problem: weights added to boxes about to slide

Physics 205A Final Exam, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problems 4.74, 4.85

A 3.0 kg box on a horizontal table is attached by a string to a hanging 1.2 kg mass. The string and pulley are ideal, but the table is not frictionless. A Physics 205A student observes that the 1.2 kg hanging mass is just sufficient enough to overcome static friction between the 3.0 kg box and the table. The student resets this experiment, adding 0.1 kg to the box, and 0.1 kg to the hanging mass. Determine whether static friction between the box (now 3.1 kg) and the table would be overcome by the hanging mass (now 1.3 kg). Show your work and explain your reasoning using a free-body diagram, the properties of forces, and Newton's laws.

Solution and grading rubric:

• p:
  Correct. Draws free-body diagrams, and applies properties of forces and Newton's laws to determine the static friction coefficient between the box and table for the first case; then for the second case determines that static friction would be overcome for the box either by discussing how (a) the hanging mass will exert a tension force on the box greater than the maximum static friction force on the box, or (b) the required static friction coefficient between the box and table to remain stationary is greater than the static friction coefficient in the first case, and since the static friction coefficient remains constant, the static friction on the box will again be overcome.
• r:
  Nearly correct, but includes minor math errors.
• t:
  Nearly correct, but approach has conceptual errors, and/or major/compounded math errors.
• v:
  Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. At least some attempt at applying properties of forces and Newton's laws.
• x:
  Implementation of ideas, but credit given for effort rather than merit. Approach does not substantively use properties of forces and Newton's laws.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Sections 70854, 70855
Exam code: finalPr0p
p: 16 students
r: 3 students
t: 8 students
v: 11 students
x: 9 students
y: 2 students
z: 2 students

A sample "p" response (from student 4585):
Another sample "p" response (from student 7582):

Physics final exam problem: spring-loaded cart collision

Physics 205A Final Exam, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Example 6.11, Problem 7.43, Comprehensive Problem 7.71

A 0.30 kg cart is held against a spring that is compressed by 0.040 m. After the 0.30 kg cart is released from the spring, it travels horizontally with a velocity of +0.45 m/s and collides and sticks together with a 1.50 kg cart that was initially at rest. Ignore friction, drag and other external forces during this brief collision. Find (a) the spring constant of the spring, and (b) the final velocity of the two stuck-together carts. Show your work and explain your reasoning using properties of collisions, energy (non-)conservation, and momentum conservation.


Solution and grading rubric:

• p:
  Correct. Applies (a) mechanical energy conservation to find spring constant of spring, and applies (b) momentum conservation to find final velocity of stuck-together carts.
• r:
  Nearly correct, but includes minor math errors. Appropriate conservation laws applied for both (a)-(b).
• t:
  Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Appropriate conservation law applied for one of (a) or (b) with correct or nearly correct result, other typically has misapplied conservation law (using momentum conservation when only mechanical energy is conserved, or kinetic energy conservation when only momentum is conserved).
• v:
  Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Some attempt at applying some conservation law.
• x:
  Implementation of ideas, but credit given for effort rather than merit. No clear attempt at applying conservation laws.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Sections 70854, 70855
Exam code: finalPr0p
p: 6 students
r: 6 students
t: 22 students
v: 14 students
x: 1 student
y: 2 students
z: 0 students

A sample "p" response (from student 8821):
A sample "t" response (from student 9603), succesfully finding only the spring constant of the spring:
Another sample "t" response (from student 1101), successfully finding only the final collision of the stuck-together carts:

Physics final exam problem: wind turbine rotational speeds

Physics 205A Final Exam, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 8.5

"Presentacion aerogenerador monopala pendular ADES"
1dezgz
youtu.be/f4JXRPAFvZI

"Enercon wind energy turbines in action"
HD1080ide
youtu.be/z6pEQevflmk

An ADES pendular wind turbine[*] consists of a long blade (mass 3,950 kg, length 18 m) and a shorter counterbalance blade (mass 5,800 kg, length 6 m). An ENERCON E-33 wind turbine[**] consists of three identical blades (each mass 1,900 kg, length 16 m). Each blade can be approximated as a uniform rod (I_{rod, at end} = (1/3)·M·L²).


Assuming that both wind turbines have approximately the same rotational kinetic energy while generating electricity, which turbine has a faster rate of rotation? Neglect drag. Show your work and explain your reasoning.

[*] Rated power 335 kW, rotor height [diameter] 36 m, 3,950 kg; pendulum 5,800 kg (pendulum arm length estimated from scale drawing)," ades.tv/en/products/pendular-wind-turbine/technical-data/id/242.
[**] "Nominal power 330 kW, blade length 15.6 m, rotor including hub/main pin 5.7 t," planning.northwarks.gov.uk/portal/servlets/AttachmentShowServlet?ImageName=233324.

Solution and grading rubric:

• p:
  Correct. Determines (a) rotational inertia of each wind turbine by summing the individual rotational inertiae of each component blade, and (b) equates rotational kinetic energies, such that the wind turbine with the smaller rotational inertia must have the faster rotation rate. (May have neglected to square rotational speed in expression for rotational kinetic energy in (b), either due to confounding rotational kinetic energy with angular momentum, or careless algebra.)
• r:
  Nearly correct, but includes minor math errors. One of (a) or (b) is correct, other part is substantive and nearly complete.
• t:
  Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Substantive but problematic efforts in both (a) and (b); or one of (a) or (b) is nearly correct, but other is missing or insubstantive.
• v:
  Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner.
• x:
  Implementation of ideas, but credit given for effort rather than merit.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Sections 70854, 70855
Exam code: finalPr0p
p: 10 students
r: 5 students
t: 7 students
v: 14 students
x: 12 students
y: 3 students
z: 0 students

A sample "p" response (from student 1223):

Online reading assignment: final questions/comments (SLO campus)

Astronomy 210, fall semester 2012
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 and comments were asked on the last reading assignment of the semester.

Selected/edited responses are given below.

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

"If I have to repeat this course would you recommend taking the lab with it?" (Not unless you are required to satisfy a science laboratory breadth requirement, and/or are very interested in satisfying your curiosity of astronomy and research in science. Otherwise the laboratory is an adjunct course that is not absolutely mandatory for success in lecture.)

"If you could live on any planet besides Earth, which would you choose and why?" (That recently discovered habitable-zone planet around Tau Ceti, 12 light years away, sounds like a pretty interesting place to live.)

"Was Mrs. P-dog really a cheerleader?" (Yes. In my dreams.)

"Since it is the holiday season, maybe you should consider not making the final too challenging. Maybe?" ("...Tests are a gift. And great tests are a great gift. To fail the test is a misfortune. But to refuse the test is to refuse the gift, and something worse, more irrevocable, than misfortune." --Lois McMaster Bujold, Shards of Hono)

"Why did you decide to teach astronomy if you have never taken an astronomy course?" (Because even more awesome than being able to learn astronomy, is being able to teach astronomy.)

"At the beginning of this course I stated that I was going to change your perception of what an 'A' student is capable of... Did I succeed?" (Yes. But every one of my 'A' students has surprised me in their own way.)

Found astronomy: revised date for Mayan Apocalypse

2012-12-19-11-39-07_321
http://www.flickr.com/photos/waiferx/8289017394/
Originally uploaded by Waifer X

According to this "Sunrise and Sunset, July-December 2012 Universal Time at Greenwich Meridian" table (David M. F. Chapman, ed., Observer's Handbook 2012, The Royal Astronomical Society of Canada, Toronto, ISBN 978-0-9813292-6-0, p. 211), the Mayan Apocalypse will apparently not occur on December 21, 2012, but on December 32, 2012. Photo by Cuesta College Physical Sciences division instruction Dr. Patrick M. Len.

Found physics: static or dynamic fluid situation?

2012-12-18_11-58-59_190
http://www.flickr.com/photos/waiferx/8284353289/
Originally uploaded by Waifer X

Physics 205A student comment on last page of final exam. Photo by Cuesta College Physical Sciences Division instructor Dr. Patrick M. Len.

Astronomy quiz question: nucleosynthesis origin of lithium

Astronomy 210 Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA

Nucleosynthesis in the first few minutes after the start of the big bang produced the:
(A) lithium in hybrid car batteries.
(B) hydrogen in Jupiter's atmosphere.
(C) iron in your blood.
(D) calcium in your bones.
(E) (More than one of the above choices.)
(F) (None of the above choices.)

Correct answer: (A)

Hydrogen is merely the raw ingredient of the universe. Light nuclides such as deuterium, helium and lithium are produced by fusion of hydrogen in the cores of main sequence stars, but deuterium and lithium are typically broken apart by the high pressures and temperatures there, such that stars cannot have produced any of the deuterium and lithium present in the universe today. These light nuclides were also produced by similar conditions in the first few minutes after the start of the big bang, but as the universe expanded and cooled, deuterium and lithium that would have been broken apart were preserved and these "fossil" nuclides remain to this day. Iron and calcium are heavier elements that can only be produced in the last stages of a supergiant, and would be dispersed to the rest of the universe during a subsequent type II supernova.

Section 70158
Exam code: quiz07sEcn
(A) : 14 students
(B) : 7 students
(C) : 5 students
(D) : 0 students
(E) : 8 students
(F) : 0 students

Success level: 45% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.56

Section 70160
Exam code: quiz07n0iC
(A) : 13 students
(B) : 5 students
(C) : 1 student
(D) : 0 students
(E) : 6 students
(F) : 0 students

Success level: 56% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.27

Astronomy quiz question: Venus' recent crust resurfacing

Astronomy 210 Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA

__________ on Venus' surface may be evidence that its crust was replaced within the last half-billion years.
(A) Widespread faults and folded mountain ranges.
(B) Lack of sedimentary rocks.
(C) Long curving ridges that cut through craters.
(D) The small number of craters.

Correct answer: (D)

The density of impact craters on the surface of a terrestrial planet is correlated with the solidification age of the crust: fewer craters corresponds to more recent solidification of the crust. The lack of plate tectonics on Venus along with its small number of craters indicates that the crust may have been replaced by widespread volcanism relatively recently.

Section 70160
Exam code: quiz07n0iC
(A) : 3 students
(B) : 0 students
(C) : 2 students
(D) : 22 students

Success level: 82% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.43

Astronomy quiz question: Venus' lack of plate tectonics

Astronomy 210 Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA

Lack of __________ on Venus' surface may be evidence it does not have plate tectonics.
(A) volcanic activity.
(B) sedimentary rocks.
(C) widespread faults and folded mountain ranges.
(D) oceans.

Correct answer: (C)

Plate tectonics ("continental drift") on Earth results in characteristic midocean rifts (where new crust is formed from the mantle) and subduction zones (where older crust is folded back down into the mantle), but also results in faults, where crustal plates move laterally past each other, and folded mountain ranges, where crustal plates are compressed and crumpled up. Lack of these features indicates that Venus does not have plate tectonics as does Earth.

Section 70158
Exam code: quiz07sEcn
(A) : 6 students
(B) : 0 students
(C) : 26 students
(D) : 2 students

Success level: 73% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33

Astronomy quiz question: visibility of belts and zones on Jupiter, Saturn

Astronomy 210 Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA

Belts and zones on Saturn are less visible than on Jupiter because they:
(A) are periodically impacted by Saturn's ring particles.
(B) have light reflected from Saturn's rings.
(C) have a metal-poor composition.
(D) lie deeper down in Saturn's atmosphere.

Correct answer: (D)

The topmost cloud layers of Jupiter and Saturn's belts and zones are warmed by sunlight; these layers are warmer for Jupiter and cooler for Saturn, such that Saturn's clouds are less buoyant and lie lower, obscured by haze.

Section 70158
Exam code: quiz07sEcn
(A) : 1 student
(B) : 6 students
(C) : 10 students
(D) : 17 students

Success level: 53% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.67

Astronomy quiz question: "ice giant" jovian planets

Astronomy 210 Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA

Uranus and Neptune are referred to as ice giants because they:
(A) are jovian planets located furthest from the sun.
(B) have prominent polar ice caps.
(C) are rich in liquid and solid forms of water.
(D) have icy rather than rocky moons.

Correct answer (highlight to unhide): (C)

While Uranus and Neptune are farthest from the sun, their atmospheres (still being primarily composed of hydrogen and helium) have a greater proportion of various forms of water than does Jupiter and Saturn.

Section 70158
Exam code: quiz07sEcn
(A) : 21 students
(B) : 6 students
(C) : 6 students
(D) : 1 student

Success level: 23% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33

Section 70160
Exam code: quiz07n0iC
(A) : 15 students
(B) : 4 students
(C) : 6 students
(D) : 0 students

Success level: 29% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33

Astronomy quiz archive: solar system

Astronomy 210 Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA

Section 70158, version 1
Exam code: quiz07sEcn


Section 70158

0- 8.0 :	** [low = 1.5]
8.5-16.0 :	*******
16.5-24.0 :	************* [mean = 21.1 +/- 7.4]
24.5-32.0 :	*********
32.5-40.0 :	*** [high = 33.0]

Section 70160, version 1
Exam code: quiz07n0iC


Section 70160

0- 8.0 :
8.5-16.0 :	** [low = 12.0]
16.5-24.0 :	*******
24.5-32.0 :	************ [mean = 25.8 +/- 6.5]
32.5-40.0 :	**** [high = 36.5]

Physics quiz question: expansion of prototype meter

Physics 205A Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Comprehensive Problem 13.101

"Platinum-Iridium meter bar"
National Institute of Standards and Technology
commons.wikimedia.org/wiki/File:Platinum-Iridium_meter_bar.jpg

The international prototype meter[*][**] was set by the distance between two markings on a platinum-iridium alloy bar (α = 8.7×10^–6 K^–1) at 0° C. To increase the distance between these markings by 0.01 mm, the temperature should be raised by:
(A) 0.001° C.
(B) 0.01° C.
(C) 0.1°.
(D) 1° C.

[*] "Differences...lie within 0.01 millimetre," bipm.org/en/CGPM/db/1/1/.
[**] "Pt90/Ir10 coefficient of thermal expansion @20-100° C," goodfellow.com/E/Platinum-Iridium.html.

Correct answer: (D)

The relation between the change in length ∆L due to a temperature change ∆T is given by:

α·∆T = ∆L/L,

such that:

∆T = ∆L/(α·L) = (0.01×10^–3 m)/((8.7×10^–6 K^–1)·(1 m)) = 1.14942528736 K,

or to one significant figure, the change in temperature is 1 K or 1° C.

Sections 70854, 70855
Exam code: quiz07Di5k
(A) : 5 students
(B) : 6 students
(C) : 4 students
(D) : 35 students

Success level: 70%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.09

Physics quiz question: chilling with a Whiskey Disk™

Physics 205A Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Practice Problem 14.5, Comprehensive Problem 14.75

"About Whiskey Disks™"
Whiskey Disks™/Rovettidesign
whiskeydisks.com/about-whiskey-disks.html

A 0.085 kg Whiskey Disk™ made of soapstone[*][**] at –10° C is placed into 0.22 kg of whiskey[***] at a temperature of 25° C. Ignore the effects of evaporation and phase changes, and heat exchanged with the environment and container. Specific heat of soapstone is 98 J/(kg·°C). Specific heat of whiskey is 3,400 J/(kg·°C). After reaching thermal equilibrium, the __________ had the greatest change in temperature.
(A) 0.085 kg Whiskey Disk™.
(B) 0.22 kg of whiskey.
(C) (There is a tie.)
(D) (Not enough information is given.)

[*] "Each disk weighs approximately 3 ounces," a.co/1TrbeVc.
[**] tulikivi.com/usa-can/fireplaces/Soapstone_characteristics.
[***] "About 3.4 J/(g·°C)," scottf.wordpress.com/2011/12/20/whiskey-stones-cooling-effectiveness/.

Correct answer (highlight to unhide): (A)

The transfer/energy balance equation is given by:

Q_ext = ∆E_disk + ∆E_whiskey,

Q_ext = m_disk·c_disk·∆T_disk + m_whiskey·c_whiskey·∆T_whiskey.

Since there are no heat exchanges with the environment or the container, the Whiskey Disk™ and the whiskey only exchange heat with each other, such that:

0 = m_disk·c_disk·∆T_disk + m_whiskey·c_whiskey·∆T_whiskey,

–m_disk·c_disk·∆T_disk = m_whiskey·c_whiskey·∆T_whiskey,

∆T_disk/∆T_whiskey = –m_whiskey·c_whiskey/m_disk·c_disk,

∆T_disk/∆T_whiskey = –((0.22 kg)·(3,400 J/(kg·°C)))/((0.085 kg)·(98 J/(kg·°C))),

∆T_disk = –89.79591837·∆T_whiskey,

(or to two significant figures, this numerical factor is –90), which means that the ∆T_disk increase in temperature is ninety times greater than the ∆T_whiskey decrease in temperature.

Sections 70854, 70855
Exam code: quiz07Di5k
(A) : 24 students
(B) : 10 students
(C) : 16 students
(D) : 0 students

Success level: 48%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.78

Physics quiz question: wide versus narrow bar

Physics 205A Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 14.49

A steel bar has twice the cross-sectional area as another steel bar of the same length. The bottom of each bar is immersed in 0° C water, while the top of each bar is heated to 75° C. (Ignore the very slight thermal expansion of these bars). The wider bar has ________ the thermal resistance of the narrower bar.
(A) one-fourth.
(B) one-half.
(C) twice.
(D) four times.
(E) (There is a tie.)

Correct answer: (B)

The thermal resistance R is given by:

R = d/(Κ·A),

where d corresponds to the (identical) length of these bars, Κ is the (identical) thermal conductivity of these bars, and A is the cross-sectional area of the bars. With A_wide = 2·A_narrow, then for these two bars:

R_wide = d/(Κ·A_wide),

R_narrow = d/(Κ·A_narrow),

The wider bar will have one-half the thermal resistance of the narrower bar:

R_wide = d/(Κ·A_wide) = d/(Κ·(2·A_narrow)) = (1/2)·R_narrow.

Sections 70854, 70855
Exam code: quiz07Di5k
(A) : 0 students
(B) : 24 students
(C) : 18 students
(D) : 3 students
(E) : 5 students

Success level: 48%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.50

Physics quiz question: Voyager 1 temperature in 1977

Physics 205A Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 14.65

"Artist concept of NASA's Voyager spacecraft"
NASA/JPL-Caltech
nasa.gov/mission_pages/voyager/voyager20120117.html

The power generated by NASA's Voyager 1 spacecraft was 420 watts in 1977, but today only 285 watts are generated.[*] Assume that all of this power is radiated into space (taken to be absolute zero). Neglect changes in the spacecraft's dimensions due to temperature changes, and assume that it is an ideal blackbody. If the surface temperature of Voyager 1 now is 194 K[**], the temperature of Voyager 1 in 1977 was:
(A) 210 K.
(B) 290 K.
(C) 470 K.
(D) 780 K.

[*] voyager.jpl.nasa.gov/spacecraft/spacecraftlife.html.
[**] "The spectrometer is likely operating at a temperature somewhat lower than –79° C," nasa.gov/mission_pages/voyager/voyager20120117.html.

Correct answer: (A)

The power output of Voyager 1 in 1977 is set equal to the net power radiated:

Power₁₉₇₇ = –e·σ·A·((T₁₉₇₇)⁴ – (0 K)⁴) = –e·σ·A·(T₁₉₇₇)⁴,

where the heat radiated per time was 420 watts, e = 1 (assuming an ideal blackbody), A is the surface area, and the surface temperature in 1977 is unknown. Similarly in 2012:

Power₂₀₁₂ = –e·σ·A·((T₂₀₁₂)⁴ – (0 K)⁴) = –e·σ·A·(T₂₀₁₂)⁴,

where the heat radiated per time is 285 watts, and the surface temperature is 194 K. Since e, σ, and A are the same for both 1977 and 2012 equations, then we can set:

–e·σ·A = –e·σ·A,

Power₂₀₁₂/(T₂₀₁₂)⁴ = Power₁₉₇₇/(T₁₉₇₇)⁴,

and solving for the temperature in 1977:

(T₁₉₇₇/T₂₀₁₂)⁴ = Power₁₉₇₇/Power₂₀₁₂,

T₁₉₇₇/T₂₀₁₂ = (Power₁₉₇₇/Power₂₀₁₂)^(1/4),

T₁₉₇₇ = T₂₀₁₂·(Power₁₉₇₇/Power₂₀₁₂)^(1/4),

T₁₉₇₇ = (194 K)·(420 watts)/(285 watts)^(1/4) = 213.748382773 K,

or to two significant figures, 210 K.

(Response (B) is T₂₀₁₂·(Power₁₉₇₇/Power₂₀₁₂); response (C) is T₂₀₁₂ + 273 K; response (D) is 4·T₂₀₁₂.)

Sections 70854, 70855
Exam code: quiz07Di5k
(A) : 10 students
(B) : 33 students
(C) : 7 students
(D) : 0 students

Success level: 20%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.47

Physics quiz archive: temperature, thermal equilibrium, heat transfer

Physics 205A Quiz 7, fall semester 2012
Cuesta College, San Luis Obispo, CA
Sections 70854, 70855, version 1
Exam code: quiz07Di5k



Sections 70854, 70855 results

0- 6 :	***** [low = 3]
7-12 :	************
13-18 :	********************** [mean = 15.2 +/- 5.4]
19-24 :	*********** [high = 24]
25-30 :

Online reading assignment: origin of life(?), are we alone? (SLO campus)

Astronomy 210, fall semester 2012
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 evidence for the origin of life on Earth, and extraterrestrial hypothesis.

Selected/edited responses are given below.

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

"The Julia Child video--comical yet informational. Anything that can make a student laugh automatically captures attention and makes the topic much more interesting."

"All life on Earth is made possible by carbon atoms. Just crazy it can be pinpointed to a single element."

"How long it took to evolve from simple compounds into complex organisms we have today. In my anthropology class we thoroughly discuss how humans have evolved from primates, but it took billions of years just to get to that point!"

"How DNA correlates to heredity and genetics. We all have genes from our mother and father and it's amazing if there are more than one offspring that each one can pick up different genes. For example a family of four the daughter could look just like the father's side of the family and the son can look like the mother's side. At the same time they both still look related."

"The crop circle 'response' to the Arecibo radio broadcast, because I want to know if there are other life forms out there!"

"Everything. Because astronomy is mind-blowing."

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

"The Drake equation, because it doesn't seem very exact. It all depends on if you think optimistically or pessimistically."

"How the Arecibo radio broadcast was coded to provide so much information about life on Earth."

"The whole 'are we alone' thing. I think it's selfish to think we are, yet why haven't 'they' tried to find us?"

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

"Doesn't it frustrate you that we will never know everything about our universe?" (That aspect of astronomy means that there will always be new and exciting things to be discovered.)

"Do you round up if our points are close to a grade cut-off?" (You do that. You round your own points up by doing the extra-credit assignments. Otherwise, if you haven't done any of them, then that won't happen.)

"Did you enjoy this semester P-dog?" (Yes. But I say that every semester.)

"Do you believe in life on other planets?" (Yes, I do. I would be willing to bet a dollar that there is (or was) life on other planets.)

"My co-worker told me that NASA found out that on December 21, 2012 the world will go dark for three days. Is that true?" (Tell your co-worker: yes. Totally going to happen. NASA would never lie. Your astronomy teacher would never lie. More seriously, check out how the Mayan calendar will roll over from the 12th to the 13th 'long-count' on December 21, 2012.)

FCI post-test comparison: Cuesta College versus UC-Davis (fall semester 2012)

Students at both Cuesta College (San Luis Obispo, CA) and the University of California at Davis were administered the 30-question Force Concept Inventory (Doug Hestenes, et al.) during the last week of instruction.

	Cuesta College Physics 205A Fall semester 2012	UC-Davis Physics 7B Summer session II 2002
N	47 students*	76 students*
low	5	3
mean	15.5 ± 5.6	12.9 ± 5.5
high	28	26

*Excludes students with negative informed consent forms (*.pdf)

Student's t-test of the null hypothesis results in p = 0.014 (t = -2.50, sdev = 5.54, degrees of freedom = 121), thus there is a significant difference between Cuesta College and UC-Davis FCI post-test scores.

The pre- to post-test gain for this semester at Cuesta College is:

Physics 205A fall semester 2012 sections 70854, 7085
<initial%>	= 32% ± 16% (N = 70)
<final%>	= 52% ± 19% (N = 47)
<g>	= 0.28 ± 0.19 (matched-pairs); 0.29 (class-wise)

This Hake gain is in line with the previous semesters' results for algebra-based introductory physics at Cuesta College (0.25-0.33), and greater than previous gains for algebra-based introductory physics at UC-Davis (0.16), and for calculus-based introductory physics at Cuesta College (0.14-0.16), as discussed in previous postings on this blog.

Notable about this Physics 205A class at Cuesta College during this fall 2012 semester is the requirement that students read and answer questions on the textbook and lecture slides before coming to lecture (in a "flipped classroom"), and the continuing use (since fall semester 2011) of flashcards rather than electronic response system "clickers" (Classroom Performance System, einstruction.com), to engage in "think-pair-share" (peer-instruction).

D. Hestenes, M. Wells, and G. Swackhamer, Arizona State University, "Force Concept Inventory," Phys. Teach. 30, 141-158 (1992).
Development of the FCI, a 30-question survey of basic Newtonian mechanics concepts.

Previous FCI results:

• Cuesta College versus UC-Davis, fall semester 2012 pre-tests.
  
• Cuesta College versus UC-Davis, fall semester 2011 pre-tests and post-tests.
  
• Cuesta College versus UC-Davis, fall semester 2009 pre-tests and post-tests.
  
• Cuesta College versus UC-Davis, spring semester 2009 pre-tests and post-tests.
  
• Cuesta College versus UC-Davis, fall semester 2008 pre-tests and post-tests.
• Cuesta College versus UC-Davis, spring semester 2008 pre-tests and post-tests.
• Cuesta College versus UC-Davis, fall semester 2007 pre-tests and post-tests.

Online reading assignment: origin of life(?), are we alone? (NC campus)

Astronomy 210, fall semester 2012
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 evidence for the origin of life on Earth, and the extraterrestrial hypothesis.

Selected/edited responses are given below.

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

"Julia Child's Miller experiment apparatus. I watched a movie about Julia Child and because I had no idea she was interested in science at all. Hah!"

"Interesting but scary finding out that humans are fairly recent living creatures. I wonder what will be the next living things or people. Amazing how things change within a blink of an eye (relatively speaking)."

"Everything, I feel insignificant in the universe."

"We're sending out complex messages about ourselves. I thought we were just listening."

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

"Life, man. Where we came from, and why?"

"The Drake equation. It looks like a long list of random letters and numbers put together. Who would come up with an equation that they can't find all the factors for?"

"Why there isn't evidence of the first forms of 'life.'"

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

"How many more homework assignments do we have? If we have the maximum amount for homework assignments is there a point in doing the assignments, besides for our own good?" (One more, after this. And yes, you can't get more points after maxing out your homework score.)

"Can you give us all 'A's' on the Final Exam as a Christmas present?" (I can do better than that. I can give you all the gift of having the opportunity of earning an 'A' for Christmas. Unless you've been naughty. Ho ho ho.)

"What are your views on the 12/21/12 'apocalypse?'" (That is the purported end of the 12th Mayan 'long count' cycle. They have a base-20 counting system, so presumably there would be eight more long counts Check out how the Mayan calendar will roll over from the 12th to the 13th 'long-count' on December 21, 2012.)

"Do you believe there are other intelligent life forms besides us?" (Yes, I do. I would bet one dollar that there is an advanced technological civilization somewhere out there.)

Astronomy current events question: most-massive black hole?

Astronomy 210L, fall semester 2012
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!)

Remco van den Bosch, Arjen van der Wel, Markus Pössel, "Black Hole Upsets Galaxy Models," November 29, 2012
http://www.mpg.de/6648360/black-hole-galaxy-models

According to researchers from the Max Planck Institute for Astronomy, the central black hole in galaxy NGC 1277 may be the most massive yet discovered, as determined by measuring:
(A) spectra of surrounding stars.
(B) emitted x-ray flares.
(C) gravitational lensing.
(D) pulsar radio beams.
(E) space-time distortions.

Correct answer: (A)

Student responses
Sections 70178, 70186, 70200
(A) : 12 students
(B) : 7 students
(C) : 6 students
(D) : 6 students
(E) : 3 students

Astronomy current events question: atmospheric changes on Titan

Astronomy 210L, fall semester 2012
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!)

Jia-Rui Cook, Elizabeth Zubritsky, Nancy Neal-Jones, "NASA's Cassini Sees Abrupt Turn in Titan's Atmosphere," November 28, 2012
http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20121128.html

NASA's Cassini spacecraft observed atmospheric changes on Saturn's moon, Titan, which may be caused by:
(A) changing seasons.
(B) Saturn's magnetic fields.
(C) hydrocarbon volcanoes.
(D) polar lightning storms.
(E) molten core circulation.

Correct answer: (A)

Student responses
Sections 70178, 70186, 70200
(A) : 11 students
(B) : 12 students
(C) : 4 students
(D) : 4 students
(E) : 3 students

Astronomy current events question: Mercury's polar ice

Astronomy 210L, fall semester 2012
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!)

NASA press release, "MESSENGER Finds New Evidence for Water Ice at Mercury's Poles," November 29, 2012
http://www.nasa.gov/mission_pages/messenger/media/PressConf20121129.html

NASA's MESSENGER spacecraft was able to confirm the presence of Mercury's __________ using three different types of measurements.
(A) warm molten core.
(B) plate tectonics.
(C) hydrocarbon lakes.
(D) polar water ice.
(E) dormant volcanoes.

Correct answer: (D)

Student responses
Sections 70178, 70186, 70200
(A) : 5 students
(B) : 1 student
(C) : 2 students
(D) : 20 students
(E) : 6 students

Online reading assignment: Physics 205B enrollment survey

Physics 205A, fall semester 2012
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 enrolling in the second semester of this general physics (Physics 205AB, algebra-based college physics) sequence.

Selected/edited responses are given below.

Next semester I am __________ take Physics 205B.

already enrolled in :	********************* [21]
planning to enroll in :	****** [6]
not planning to :	*********** [11]
(not yet sure/undecided) :	******** [8]

If you are not taking Physics 205B next semester, are you planning on enrolling in a later semester?

Yes. :	*********** [11]
Maybe. :	*********** [11]
No. :	*************** [15]

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

"I really want a 'B' in your class. really really badly." (Good. You won't get it unless you first want it.)

"Is there a summer course?" (Physics 205B: no. Physics 205A: yes, depending on budget cuts.)

"I really enjoyed this class P-Dog. You definitely made this easier to understand than my high school teacher did." (I pity your high school physics teacher.)

"What kind of concepts do we learn in Physics 205B? Is 205B harder than 205A? Will you teach Physics 205B?" (Lenses, interference, electromagnetism, circuits, and some modern physics. Like the second-half of Physics 205A, we go through an average of one chapter a week. Yes, I will be there for you. Good times ahead.)

"How well do you think we did as a class this semester?" (We'll see how well you do on the conceptual Physics Survey B post-test, compared to UC-Davis students.)

"No question, but a comment. I absolutely love your way of grading. The way the scale is written out is my favorite out of any class I have had. I know exactly how many points I need to make it to the next grade at all times throughout the class. It may have been daunting to start with an 'F' and earn your way up to a better grade, but I think it just makes students try harder. Students don't have to worry about a bad test or quiz lowering your grade. Thank you."

"I thought I didn't have to take physics for my major, but I changed schools and now I need both semesters! I'm so glad I stuck with it. Thanks for being an awesome teacher!"

Astronomy midterm question: small hot stars always more luminous than cool big stars?

Astronomy 210 Midterm 2, fall semester 2012
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board(*) was asked and answered:

Pd: Is it possible that a small hot star and a cool big star [located the same distance from us] can be equally bright?
Star Dust: Small-hot is [always] more luminous than cool-big.

Discuss why this answer is not correct, and how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.

*Adapted from: http://answers.yahoo.com/question/index?qid=20120928201352AA8dDbB.

Solution and grading rubric:

• p = 20/20:
  Correct. Uses Wien's law, the Stefan-Boltzmann law and/or interprets H-R diagram to show that small, hot stars can be either (a) equally luminous, or (b) less luminous than cool, big stars.
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors.
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use Wien's law, H-R diagram and/or the Stefan-Boltzman law.
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on Wien's law, H-R diagram and/or the Stefan-Boltzman law.
• y = 2/20:
  Irrelevant discussion/effectively blank.
• z = 0/20:
  Blank.

Grading distribution:
Section 70160
Exam code: midterm02NuF7
p: 20 students
r: 5 students
t: 1 student
v: 1 student
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 5411) demonstrating how a small hot star could be as luminous as a large cool star:
Another sample "p" response (from student 0716) demonstrating how a small hot star could be less luminous than a large cool star:

Astronomy midterm question: small cool stars or large hot stars in young cluster?

Astronomy 210 Midterm 2, fall semester 2012
Cuesta College, San Luis Obispo, CA

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

dk: How can we tell that a star cluster is young (only 10 million years old or so)? Small, cool stars, [or] large, hot stars [on the main sequence]?
pl: Large, hot stars [on the main sequence] means the cluster is young.

Discuss why this answer is correct, and how you know this. Explain using the properties and evolution of stars.
[*] answers.yahoo.com/question/index?qid=20070625180152AADZE8x.

Solution and grading rubric:

• p:
  Correct. Understands that massive (large, hot) stars evolve faster than low-mass (small, cool) stars, such a younger star cluster will have massive stars that are on the main-sequence, while an older star cluster will have low-mass stars on the main-sequence.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least understands correlation between mass and main sequence lifetimes.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution of stars.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 70160
Exam code: midterm02NuF7
p: 22 students
r: 2 students
t: 3 students
v: 0 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 0716):
Another sample "p" response (from student 7783), appealing to the "house party" model:

Astronomy midterm question: different apparent magnitude, but same absolute magnitude stars?

Astronomy 210 Midterm 2, fall semester 2012
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board(*) was asked and answered:

P-dog: Can a star with apparent magnitudes of +1, and a star with apparent magnitude –1 have the same absolute magnitude?
NoPlate: Yes, [if] the star with –1 [apparent] magnitude [is located] much closer...

Discuss why this answer is correct, and how you know this. Explain using the properties of apparent magnitude, absolute visual magnitude, and distance.

*Adapted from: http://answers.yahoo.com/question/index?qid=20121105203518AAOq4ea.

Solution and grading rubric:

• p = 20/20:
  Correct. Understands difference between apparent magnitude (m) values and absolute magnitude (M_V) values, and that the two stars can have the same absolute magnitude (same brightness if both located 10 parsecs away) if the star that is actually closer seems bright (m = +1) and the star that is actually farther away seems dimmer (m = -1).
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least understands the difference between apparent (m) and absolute (M_V) magnitudes, and that smaller positive (or more negative) magnitudes are brighter.
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Garbled definitions/relations between d, m, and M_V.
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on apparent magnitudes, absolute magnitudes, and distances.
• y = 2/20:
  Irrelevant discussion/effectively blank.
• z = 0/20:
  Blank.

Grading distribution:
Section 70158
Exam code: midterm02s0Ur
p: 18 students
r: 1 student
t: 9 students
v: 5 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 0916):

Astronomy midterm question: massive main-sequence stars and white dwarfs in same star cluster?

Astronomy 210 Midterm 2, fall semester 2012
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board(*) was asked and answered:

Bob: What's wrong with a [star cluster that has massive] main-sequence stars, and white dwarfs?
Alexis: [These stars] could not have formed from the same hydrogen cloud.

Discuss why this answer is correct, and how you know this. Explain using the properties and evolution of stars.

*Adapted from: http://answers.yahoo.com/question/index?qid=20111029161602AATbPgo.

Solution and grading rubric:

• p = 20/20:
  Correct. Understands that (a) stars in the same cluster are all born at the same time, (b) massive stars evolve faster than medium-mass stars, and (c) white dwarfs are the remnant of medium-mass stars (after going through its giant and planetary nebula phases), such that it is not possible for a massive star on the main-sequence to be the same age as a medium-mass star that has already ended its main-sequence lifetime to become a white dwarf.
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. May confuse white dwarfs (medium-mass stars that have long ago ended their main-sequence lifetime) with red dwarfs (low-mass stars on the main-sequence).
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least understands correlation between mass and main sequence lifetimes.
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution of stars.
• y = 2/20:
  Irrelevant discussion/effectively blank.
• z = 0/20:
  Blank.

Grading distribution:
Section 70158
Exam code: midterm02s0Ur
p: 5 students
r: 13 students
t: 8 students
v: 5 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 0916):
Another sample "p" response (from student 0402), appealing to the "house party" model:

Astronomy midterm question: big bang expansion, not explosion?

Astronomy 210 Midterm 2, fall semester 2012
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board(*) was asked and answered:

strange questioner: Big bang: explosion or expansion? Most...sources say big bang as explosion, some others say it is wrong to say explosion and it's only expansion.
green meklar: It is more like an expansion [than an explosion].

Discuss why this answer is correct, and how you know this. Explain using observations and evidence related to the Hubble law.

*Adapted from: http://answers.yahoo.com/question/index?qid=20120820231957AAhZq7N.

Solution and grading rubric:

• p = 20/20:
  Correct. Discusses (a) Hubble's law (recession velocity of galaxies is proportional to distance), (b) evidence for Hubble's law (greater redshift of absorption lines for distant galaxies compared to nearby galaxies), and (c) relates this to the expansion of space, as opposed to an explosion (where the velocity of particles is inversely proportional to the distance from the center of the explosion, and also has a unique center).
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Discusses two of the three (a)-(c) points in (p).
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Discussion of only one of the three points (a)-(c) in (p) is complete.
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion based on evidence of the earlier stages in the history of the universe, with little or no substantive discussion of Hubble's law.
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit.
• y = 2/20:
  Irrelevant discussion/effectively blank.
• z = 0/20:
  Blank.

Grading distribution:
Section 70158
Exam code: midterm02s0Ur
p: 4 students
r: 11 students
t: 10 students
v: 6 students
x: 2 students
y: 0 students
z: 0 students

Section 70160
Exam code: midterm02NuF7
p: 7 students
r: 9 students
t: 9 students
v: 2 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1105):
Another sample "p" response (from student 2344):