Physics clicker question: temperature and temperature changes

Physics 5A, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problems 13.2, 13.4, Conceptual Question 13.3

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the start of their learning cycle:

[0.6 participation points.] Which one of the following temperatures is the warmest?
(A) 10° C.
(B) 10 K.
(C) 10° F.
(D) (I'm lost, and don't know how to answer this.)

Sections 4987, 4988
(A) : 5 students
(B) : 14 students
(C) : 0 students
(D) : 0 students

Correct answer: (A)

The coldest temperature is (B), which is most nearest to absolute zero (perhaps demonstrating the students' unfamiliarity with the Kelvin scale). Between (A) and (C), 10° F is below freezing (32° F), while 10° C is above freezing (0° C), so response (A) is the warmest temperature.

[Follow-up question]

[0.6 participation points.] Which one of the following temperature changes represents the largest amount of cooling?
(A) –10° C.
(B) –10 K.
(C) (Both changes in temperature corresponds to the same amount of cooling.)
(D) (Both the initial and final temperatures need to be given.)
(E) (I'm lost, and don't know how to answer this.)

Sections 4987, 4988
(A) : 10 students
(B) : 10 students
(C) : 2 students
(D) : 1 student
(E) : 0 students

Correct answer: (C)

Apparently these students are not at all familiar with temperature scales and changes in temperatures (preoccupied on an impending semi-comprehensive midterm on chapters previous to this introduction to thermodynamics?). It is pointed out to them after these clicker questions that T (°C) ≠ T (K), but they are related by an "offset":

T (°C) = T (K) - 273.15.

However, even though these temperatures are not equivalent, changes in these temperatures are, such that:

delta_T (°C) = delta_T (K).

Students are warned that this property of temperature changes will come in handy throughout thermodynamics (expansion, heat, etc. calculations).

Astronomy clicker question: dark energy evidence

Astronomy 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q11.3

Students were asked the following clicker question (Classroom Performance System, einstruction.com) near the start of their learning cycle.

[0.3 points.] How do we know that there is dark matter in the halo of the Milky Way (above/below its disk)?
(A) The temperature of empty space is not really absolute zero.
(B) Stars just outside of the Milky Way appear dimmer than they should be.
(C) Stars in the inner and outer parts of the disk orbit the center of the Milky Way at the same speed.
(D) The Milky Way has more black holes than expected.

Correct answer: (withheld until after whole-class discussion)

Student responses
Section 4160
(A) : 5 students
(B) : 19 students
(C) : 4 students
(D) : 3 students

Whole-class discussion
Instructor: "So why did you guys choose (B)?"

Student 1: "Because dark matter is dark?"

Instructor: "Fine. And what's the deal with (C)--does this look like Kepler's third law?"

Student 2: (Explains why it is not.)

Instructor: "Yes... That would certainly be strange, to see inner and outer orbits having the same speed. But that is exactly what is seen for the stars that orbit around the center of the Milky Way."

Class: "What?!?"

Well, that's the way it might have been said.

Correct answer: (C)

FCI post-test comparison: Cuesta College versus UC-Davis

Students at both Cuesta College (San Luis Obispo, CA) and the University of California at Davis were administered the Force Concept Inventory (Doug Hestenes, et al.) during the last week of instruction, in order to follow up on the pre-test results from the first week of instruction (which showed no statistical difference between pre-test scores).

     Cuesta College    UC-Davis
     Physics 5A        Physics 7B
     Spring Semester   Summer Session II
     2008              2002
N    30 students       76 students
low   6                 3
mean 14.0 +/- 5.0      12.9 +/- 5.5
high 27                26

A "Student" t-test of the null hypothesis results in p = 0.34, thus there is no 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 5A Spring Semester 2008 sections 4987, 4988
<initial%> = 33% +/- 16% (N = 46)
  <final%> = 47% +/- 17% (N = 30)
       <g> = 0.21 +/- 0.15 (matched-pairs); 0.20 (class-wise)

This is comparable to the gains for algebra-based introductory physics at Cuesta College (0.23), 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 5A class at Cuesta College is the implementation of electronic response system "clickers" (Classroom Performance System, einstruction.com), compared to the traditional lecture of Physics 8A at Cuesta College, and the reformed peer-instruction centered approach at UC-Davis. More analysis on the impact of using clickers on this introductory physics class will be forthcoming.

Astronomy quiz question: type Ia supernovae

Astronomy 10 Quiz 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q10.3

[3.0 points.] Which one of the following choices best explains why an isolated white dwarf cannot explode as a type Ia supernova?
(A) There is no companion star to heat up.
(B) There is no external source of hydrogen.
(C) There is no companion star to distort spacetime.
(D) It expended all of its extra energy during the planetary nebula phase.
(E) There is not enough degeneracy pressure.

Correct answer: (B)

If there is no companion star to transfer hydrogen to a white dwarf, then the white dwarf star cannot collect and compact this material onto its surface, making it undergo fusion to undergo a type Ia supernova (or a mere nova) explosion.

Student responses
Section 5166
(A) : 8 students
(B) : 17 students
(C) : 4 students
(D) : 6 students
(E) : 7 students

Previous post:
Astronomy in-class activity: compact objects with companion stars.

Astronomy quiz question: x-ray bursts

Astronomy 10 Quiz 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q10.3

[3.0 points.] Which one of the following choices best explains why an isolated neutron star cannot have repeated x-ray bursts?
(A) There is no companion star to heat up.
(B) There is no companion star to distort spacetime.
(C) It expended all of its extra energy during its type II supernova.
(D) There is no external source of hydrogen.
(E) There is not enough degeneracy pressure.

Correct answer: (D)

If there is no companion star to transfer hydrogen to a neutron star, then the neutron star cannot collect and compact this material onto its surface, making it undergo fusion to produce an x-ray burst.

Student responses
Section 4160
(A) : 7 students
(B) : 1 student
(C) : 10 students
(D) : 16 students
(E) : 0 students

Previous post:
Astronomy in-class activity: compact objects with companion stars.

Astronomy quiz question: accretion disk blackbody radiation

Astronomy 10 Quiz 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q10.3

[3.0 points.] Which one of the following choices best explains how accretion disks emit intense ultraviolet, and/or x-ray blackbody radiation?
(A) Heat generated from friction.
(B) Electrons jump down to lower orbits.
(C) Electrons flip their spins.
(D) Curvature of spacetime.
(E) Hydrogen fuses into helium.

Correct answer: (A)

A companion star of a compact object (white dwarf, neutron star, or black hole) may be close enough such that it will overflow its Roche lobe when it becomes a giant or superigant, thus transferring hydrogen to the compact object. This infalling hydrogen collects into an accretion disk surrounding the compact object, and due to Kepler's third law, the outer part of the disk orbits slower than the inner part of the disk. Due to the density of the disk, the difference in speeds between adjacent parts causes friction, producing enough heat for the disk to become incandescent, thus emitting blackbody radiation.

Student responses
Section 5166
(A) : 9 students
(B) : 17 students
(C) : 2 students
(D) : 3 students
(E) : 5 students

Previous post:
Astronomy in-class activity: compact objects with companion stars.

Astronomy quiz question: black holes with companion stars

Astronomy 10 Quiz 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q10.3

[3.0 points.] Which one of the following statements best explains why x-rays are observed from close binary systems comprised of black holes with companion stars?
(A) Only x-ray photons are fast enough to escape from black holes.
(B) Electrons falling into lower energy orbitals release x-ray photons.
(C) Black holes can only emit x-ray photons.
(D) Accretion disks surrounding black holes emit very hot blackbody radiation.
(E) Companion stars orbiting black holes emit very hot blackbody radiation.

Correct answer: (D)

A companion star of a black hole may be close enough such that it will overflow its Roche lobe when it becomes a giant or superigant, thus transferring hydrogen to the black hole. This infalling hydrogen collects into an accretion disk surrounding the black hole, heating up in the process to become incandescent, emitting blackbody radiation.

Student responses
Section 4160
(A) : 3 students
(B) : 5 students
(C) : 6 students
(D) : 16 students
(E) : 4 students

Previous post:
Astronomy in-class activity: compact objects with companion stars.

Astronomy quiz question: mass transfer in close-pair binaries

Astronomy 10 Quiz 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q10.2

[3.0 points.] Which one of the following choices best explains why the Roche lobes of two stars in a close-pair (mass-exchanging) binary system get smaller as they begin to orbit closer to each other?
(A) Gravitational forces get weaker.
(B) Centrifugal forces get stronger.
(C) Degeneracy pressure increases.
(D) Hydrogen is transferred slowly.
(E) Repeated nova explosions disrupts hydrogen transfer.

Correct answer: (B)

Due to conservation of angular momentum, the orbital speeds of the stars will increase as their separation distance decreases (as they would during hydrogen transfer from a more massive star to a less massive star). This will increase the centrifugal forces exerted on them, decreasing the size of their Roche lobes.

Student responses
Section 5166
(A) : 5 students
(B) : 29 students
(C) : 4 students
(D) : 7 students
(E) : 2 students

Related post:
Astronomy in-class activity: mass transfer in close-pair binaries.

Astronomy quiz question: mass transfer in close-pair binaries

Astronomy 10 Quiz 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q10.2

[3.0 points.] Which one of the following statements best explains why the transfer of hydrogen in a close-pair binary system from a less massive star to a more massive star happens very slowly?
(A) There is not much hydrogen left in the less massive star.
(B) They move farther apart from each other.
(C) The less massive star has not yet ended its main sequence lifetime.
(D) The more massive star produces strong winds.
(E) (None of above choices (A)-(D), as it is not possible for hydrogen to be transferred from a less massive star to a more massive star.)

Correct answer: (B)

When a less massive star is transferring hydrogen to a more massive star, their masses become more unequal, such that their separation distance increases. This decreases their orbital speeds, decreasing centrifugal forces, resulting in enlarging their Roche lobes, making it more difficult for the less-massive star to overflow its Roche lobe. This will slow down, and eventually stop the transfer of hydrogen from the less massive to the more massive star.

Student responses
Section 4160
(A) : 11 students
(B) : 11 students
(C) : 6 students
(D) : 1 student
(E) : 5 students

Related post:
Astronomy in-class activity: mass transfer in close-pair binaries.

Education research: "clicker zombies"

*POOF* Mah sleeping spell wrkd!, by Firestar779
icanhascheezburger.com
May 8, 2008

With 16 clicker questions in a weekly, three hour evening lecture in introductory astronomy, students stay awake only enough to click in. With so many clicker questions interspersed throughout lecture (approximately 10 minutes per clicker question) with not enough student-student interaction, results in the above dramatization--many students with heads down, too exhausted to take notes, only rousing themselves to make the obligatory effort to click in.