P-dog's blog: boring but important

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

20130528

Astronomy final exam question: IAU classification of Earth's moon fragments in Oblivion (2013)

Astronomy 210 Final Exam, spring semester 2013
Cuesta College, San Luis Obispo, CA

In the movie Oblivion (Universal Pictures, 2013), Earth's moon is broken into a large irregular-shaped fragment surrounded by much smaller debris, presumably all of which orbit Earth. Classify the large irregular-shaped fragment, using the International Astronomical Union classification scheme.

Solution and grading rubric:

p:
Correct. Of the three IAU requirements (orbits the sun, has a rounded shape, cleared/dominates its orbit) this large fragment fails all three, but failing the first requirement classifies it as a satellite/moon of Earth.
r:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Understands which IAU requirements this large fragment satisfies or does not satisfy, but misclassifies typically as solar system debris.
t:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problematic discussion of IAU requirements.
v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion only tangentially related to the IAU requirements.
x:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion unrelated to the IAU requirements.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Section 30674
Exam code: finalnNz2
p: 12 students
r: 6 students
t: 6 students
v: 0 students
x: 1 student
y: 1 student
z: 1 student

Section 30676
Exam code: finals56G
p: 8 students
r: 16 students
t: 2 students
v: 7 students
x: 4 students
y: 1 student
z: 1 student

A sample "p" response (from student 8387):

Another sample "p" response (from student 1019):

A whimsical sample "y" response (from student 9999):

Astronomy final exam question: comparing relative potential habitability of Kepler-62e, Kepler-62f

Astronomy 210 Final Exam, spring semester 2013
Cuesta College, San Luis Obispo, CA

According to a NASA press release[*], the star Kepler-62 is a medium-mass main-sequence star somewhat similar to the sun, and:

Kepler-62 is home to two habitable zone worlds, Kepler-62f and Kepler-62e. Kepler-62f [orbiting farther out] is only 40 percent larger than Earth... Kepler-62e [orbiting closer in] is roughly 60 percent larger than Earth.

Determine which planet (62f or 62e) would be more likely to have an atmosphere with a moderate greenhouse effect and a moderate temperature for liquid oceans to be present. Explain using the properties of greenhouse gases and geological activity.

[*] http://www.nasa.gov/mission_pages/kepler/multimedia/images/kepler-62-diagram.html.

Solution and grading rubric:

p = 20/20:
Correct. Recognizes how (1) mass determines atmosphere thickness (more massive planet Kepler 62e would outgas more atmosphere, and better gravitationally retain this atmosphere); and how (2) distance from sun determines the temperature of an atmosphere (Kepler 62e being closer to its star would absorb and retain more heat). Thus Kepler 62e would be more susceptible to higher temperatures and more likely evaporate its oceans, while less mass and further out Kepler 62f would be more likely to have moderate temperatures for liquid oceans.
r = 16/20:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. One of two points (1)-(2) correct, other is problematic/incomplete. May argue that Kepler 62f would have an atmosphere that is too thin, and too little heat absorbed for moderate temperatures for liquid oceans, making Kepler 62e the more ideal candidate.
t = 12/20:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Both points (1)-(2) problematic/incomplete, or one point correct while other is missing.
v = 8/20:
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 density and greenhouse effect.
x = 4/20:
Implementation/application of ideas, but credit given for effort rather than merit. Discusses factors other than relevant to the greenhouse effect.
y = 2/20:
Irrelevant discussion/effectively blank.
z = 0/20:
Blank.

Grading distribution:
Section 30674
Exam code: finalnNz2
p: 4 students
r: 7 students
t: 8 students
v: 6 students
x: 1 student
y: 1 student
z: 0 students

Section 30676
Exam code: finals56G
p: 3 students
r: 7 students
t: 17 students
v: 9 students
x: 0 students
y: 1 student
z: 2 students

A sample "p" response (from student 0211):

Another sample "p" response (from student 6608):

A sample "y" response (from student 0426):

Another sample "y" response (from student 9251):

Physics final exam question: light ray at Plexiglas®-air interface

Physics 205B Final Exam, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 23.11, Comprehensive Problem 23.91

Light in Plexiglas® (index of refraction[*] of 1.491) is incident at an angle of 41.5° at the interface between Plexiglas® and air (index of refraction of 1.000). (Drawing is not to scale.) If the incident angle of the beam of light in Plexiglas® is increased slightly from 41.5° to 42.0°, describe what will happen to the beam. Explain your reasoning using the properties of light and refraction.

[*] wiki.pe/Acrylic_glass.

Solution and grading rubric:

p:
Correct. With an incident angle less than the critical angle, light will still be transmitted out into air instead of totally internally reflected back into Plexiglas® (there will also be a partially reflected ray in Plexiglas® as well). Directly calculates the critical angle to compare to the incident angle, or attempts a (successful) trial solution for the transmitted angle in air using Snell's law.
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.
x:
Implementation/application of ideas, but credit given for effort rather than merit.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 30882
Exam code: finalpL3x
p: 19 students
r: 1 student
t: 5 students
v: 5 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1408), first attempting a trial solution to Snell's law (which would indicate no total internal reflection):

Another sample "p" response (from student 6377), explicitly solving for the critical angle first, and then noting that the incident angle is smaller than the critical angle:

Physics final exam question: total electric field of two fixed source charges

Physics 205B Final Exam, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 16.35

Two point charges are held at fixed locations. A +1.0 nC charge is at the origin, and a second –1.5 nC charge is at x = +2.0 cm. Discuss why the electric field to the left of both charges  (x < 0) is weaker than the electric field to the right of both charges (+2.0 cm < x). Explain your answer using the properties of charges, electric fields, and superposition.

Solution and grading rubric:

p:
Correct. Discusses:
1. that to the left or to the right of both charges, the electric fields from each charge point in different directions, thus the (total) electric field at either location will be the difference of the two electric field magnitudes;
2. the negative charge will have a greater magnitude electric field compared to the positive charge's electric field at comparable distances;
3. such that there is a greater difference between the opposing electric fields to the right of both charges than to the left of both charges, resulting in a stronger (total) electric field to the right of both charges.
r:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Chooses stronger electric field contribution to show greater magnitude of total electric field without explicit demonstration of superposition.
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.
x:
Implementation/application of ideas, but credit given for effort rather than merit.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 30882
Exam code: finalpL3x
p: 1 student
r: 5 students
t: 10 students
v: 10 students
x: 1 student
y: 1 student
z: 2 students

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

Physics final exam question: squeezing a paper-dielectric capacitor

Physics 205B final exam, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problems 17.55, 17.57

A parallel-plate capacitor is constructed by placing two foil sheets between different pages in a phone book. The capacitor is then connected to a 9 V battery. As the phone book is pressed down upon to squeeze the pages between the foil sheets, discuss why the capacitor will store more charge. Explain your reasoning using the properties of capacitors.

Solution and grading rubric:

p:
Correct. Discusses:
1. how capacitance is inversely proportional to the separation distance between the plates, so squeezing the plates closer together will increase the capacitance;
2. increasing the capacitance while keeping the electric potential constant will result in increasing the charge stored on the capacitor plates.
r:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. One of the two arguments in (p) is only nearly complete, or has minor inconsistencies.
t:
Nearly correct, but argument has conceptual errors, or is incomplete. Only one of the two arguments in (p) is complete, the other is missing or only implied.
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.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 30882
Exam code: finalpL3x
p: 17 students
r: 5 students
t: 8 students
v: 0 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 4444), with a happy-face unicorn:

A sample "t" response (from student 8235), not explicitly discussing how an increase in "catpacitance" (with electric potential held constant) would then result an increase in charge:

Physics final exam question: incorrect Feynman diagram

Physics 205B final exam, spring semester 2013
Cuesta College, San Luis Obispo, CA

The Feynman diagram (A) correctly shows an electron capture decay process, where a proton and an electron interact to convert into a neutron and a neutrino. Discuss why the other Feynman diagram (B) showing an antineutrino interacting with a proton to convert into a neutron and positron is incorrect. Explain your reasoning using the properties of Feynman diagrams, particles and antiparticles, and interactions.

Solution and grading rubric:

p:
Correct. Discusses (1) how the second Feynman diagram violates the in-out path vertex rule, and/or (2) draws a corrected Feynman diagram for an antineutrino and proton respectively turning into a positron and neutron after the interaction.
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.
x:
Implementation/application of ideas, but credit given for effort rather than merit.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 30882
Exam code: finalpL3x
p: 16 students
r: 1 student
t: 5 students
v: 3 students
x: 2 students
y: 1 student
z: 2 students

A sample "p" response (from student 1408):

A sample "x" response (from student 8325), with at least some demonstration of understanding charge flow conservation:

Physics final exam problem: reconstruction of Galileo's telescope

Physics 205B Final Exam, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problems 24.49, 24.51, Comprehensive Problem 24.63

The Museo Galileo Institute and Museum of the History of Science in Florence, Italy has several of Galileo's telescopes in its collection[*]:

Original telescope [late 1609-early 1610] made by Galileo consisting of a main [adjustable length] tube with separate housings at either end for the objective and the eyepiece... The objective [has] a focal length of 980 mm... The original eyepiece was lost. The instrument's magnification is [–]21×.

Assume that the lost eyepiece was a converging lens. Determine (a) the focal length of the eyepiece and (b) the length of the telescope (as measured from the objective to the eyepiece) when used to observe distant objects. Show your work and explain your reasoning.

[*] brunelleschi.imss.fi.it/museum/esim.asp?c=405002.

Solution and grading rubric:

p:
Correct. Determines (1) the focal length of the eyepiece, and (2) the length of the telescope.
r:
Nearly correct, but includes minor math errors.
t:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. At least has focal length of eyepiece, and some attempt in finding the length of the telescope.
v:
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. At least attempts to use telescope equations.
x:
Implementation of ideas, but credit given for effort rather than merit. Use of microscope equations, etc.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 30882
Exam code: finalpL3x
p: 17 students
r: 2 students
t: 7 students
v: 0 students
x: 2 students
y: 1 student
z: 1 student

A sample "p" response (from student 1224):

A sample "y" response (from student 1101), invoking lyrics from Queen's "Bohemian Rhapsody":

Physics final exam problem: effect of removing light bulb from circuit

Physics 205B Final Exam, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Questions 18.22, 18.23, Problems 18.40, 18.41

Two identical light bulbs (R₁ = R₂ = 2.0 Ω), a third light bulb (r = 0.50 Ω), and an ideal 9.0 V emf source are connected as shown in the diagram at right. If the R₁ light bulb is completely removed from the circuit (and not replaced with anything, leaving that part of the circuit open), determine whether the brightness of the r light bulb would decrease, increase, or remain the same. Show your work and explain your reasoning.

Solution and grading rubric:

p:
Correct. Uses either a quantitative or qualitative argument to show that (1) the equivalent resistance is greater when the R₁ light bulb is disconnected from the circuit, resulting in (2) less current flowing through the r light bulb, (3) making it dissipate less power, and thus is dimmer.
r:
Nearly correct, but includes minor math errors.
t:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Only one step in (p) correct: typically finding the resistances r and R.
v:
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Problematic application of equivalent resistance, Ohm's law (and/or Kirchhoff's circuit rules), and power.
x:
Implementation of ideas, but credit given for effort rather than merit.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 30882
Exam code: finalpL3x
p: 3 students
r: 3 students
t: 8 students
v: 14 students
x: 0 students
y: 2 students
z: 0 students

A sample "p" response (from student 1224):

A sample "p" response (from student 1337):

Physics final exam problem: tritium-powered luminous wristwatches

Physics 205B Final Exam, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 39.37, Comprehensive Problem 29.79(a)

The following posts were made on an online discussion board[*]:

LZ: Well from what I've been told, the tritium tubes in a Marathon watch[**] last up to 20 years...
sharp: The "lasts for 20 years" is a misnomer. Tritium has a half-life of 12.3 years, which means that 12.3 years after a set amount of tritium is created, half of its radioactivity will be gone: half its brightness. It doesn't mean in 20 years the light will just turn off, but that some marketing guy thinks that in 20 years the brightness will be too dim to be usable (or long after the watch falls apart).

Assume that the brightness of a tritium-powered watch is proportional to the activity. Determine the percent decrease in brightness of a tritium-powered watch in 20 years. Show your work and explain your reasoning.

[*] "Tritium Watches / Pros and Cons," edcforums.com/threads/tritium-watches-pros-and-cons.48729/.
[**] topspecus.com/shop/category/marathon-watches/.

Solution and grading rubric:

p:
Correct. Finds activity decreases to 32% of its original value, corresponding to a decrease by 68% from its original value.
r:
Nearly correct, but includes minor math errors. Finds activity decreases to 32% of its original value, but garbles the percent decrease by calculation.
t:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Only has activity decreasing to 32% of its original value.
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 30882
Exam code: finalpL3x
p: 13 students
r: 1 student
t: 4 students
v: 7 students
x: 2 students
y: 1 student
z: 2 students

A sample "p" response (from student 2121), using the half-life decay equation:

20130522

Student scribble: happy calculator busting out numbers

2013-05-22_17-28-25_184
http://www.flickr.com/photos/waiferx/8795354602/
Originally uploaded by Waifer X

Physics 205B student doodle on Final Exam, spring semester 2013, Cuesta College, San Luis Obispo, CA. Photo by Cuesta College Physical Sciences Division instructor Dr. Patrick M. Len.

Physics quiz question: radioactive decay age

Physics 205B Quiz 7, spring semester 2013
Cuesta College, San Luis Obispo, CA

Two samples have certain amounts of a radioactive isotope, an embedded gaseous daughter element, and inert material (which is not involved in the decay process). As determined by radioactive dating, sample A is __________ than sample B.
(A) older.
(B) younger.
(C) (There is a tie.)
(D) (Cannot be determined.)

Correct answer (highlight to unhide): (A)

The solidification age of a sample (how long ago has it been since it was last molten) is determined by the ratio of decay products to its unstable isotopes. A larger ratio of decay products to unstable isotopes corresponds to a sample with a very old solidification age.

Sample A started with 24 unstable isotope squares when it first solidified (as any gaseous decay products would have been released when it was melted), of which 8 remain today, such that it has 33% of its original radioactivity today. Sample B started with 16 unstable isotope squares when it first solidified, of which 8 remain today, such that it has 50% of its original radioactivity today.

Section 30882
Exam code: quiz07f3yN
(A) : 31 students
(B) : 1 student
(C) : 0 students
(D) : 0 students

Success level: 97%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.07

Physics quiz question: interpreting Compton scattering Feynman diagram

Physics 205B Quiz 7, spring semester 2013
Cuesta College, San Luis Obispo, CA

The Feynman diagram shown at right depicts:
(A) an electron absorbing a photon, then emitting a photon.
(B) an electron emitting a photon, then absorbing a photon.
(C) a positron absorbing a photon, then emitting a photon.
(D) a positron emitting a photon, then absorbing a photon.
(E) pair production, then annihilation.
(F) annihilation, then pair production.

Correct answer: (A)

Since time runs from left-to-right in this Feynman diagram, an electron (which is traveling left-to-right) absorbs a photon in the first vertex, then at the second vertex this electron emits a photon. (N.b. This is a Feynman diagram for Compton scattering.)

If the time axis were instead diagonally lower-left-to-upper-right (which is not the case here), then a photon would create a positron and electron pair, of which the electron would later meet up with another positron, annihilating each other to produce a photon.

Section 30882
Exam code: quiz07f3yN
(A) : 23 students
(B) : 3 students
(C) : 0 students
(D) : 1 student
(E) : 3 students
(F) : 2 students

Success level: 72%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.36

20130521

Physics quiz question: interpreting β^– decay Feynman diagram

Physics 205B Quiz 7, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Multiple-Choice Question 29.1

A Feynman diagram is shown at right. A __________ exits this interaction event.
(A) neutron.
(B) neutrino.
(C) positron.
(D) proton.
(E) (More than one of the above choices.)
(F) (None of the above choices.)

Correct answer (highlight to unhide): (D)

This diagram shows β^- decay, where a neutron transforms into a proton, and the intermediate W^- particle decays into an electron and an antineutrino, as shown by the left-to-right electron arrow, and a right-to-left neutrino arrow (corresponding to an antineutrino progressing left-to-right as time progresses). Thus of the above four choices, only a proton leaves this interaction event, as a neutron enters it, and an antineutrino and electron leave the interaction event (but neither of which are listed as choices).

Section 30882
Exam code: quiz07f3yN
(A) : 4 students
(B) : 6 students
(C) : 2 students
(D) : 9 students
(E) : 11 students
(F) : 0 students

Success level: 29%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.19

Physics quiz question: decay(s) for decreasing proton number

Physics 205B Quiz 7, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Multiple-Choice Question 29.1

Which decay mode decreases the number of protons in a nucleus?
(A) α.
(B) β^–.
(C) β⁺.
(D) electron capture.
(E) γ.
(F) (More than one of the above choices.)
(G) (None of the above choices.)

Correct answer: (F)

For α decay, a helium nucleus with two protons and two neutrons is emitted from the unstable nucleus; for β⁺ decay, a proton is converted into a neutron (and emits a positron and a neutrino); for electron capture, a proton combines with an electron to convert into a neutron (and emits a neutrino); all of these processes decrease the number of protons in a nucleus.

For γ decay a photon is emitted, and there is no change in the number of protons (or neutrons) in the nucleus. For β^- decay, a neutron transforms into a proton (and emits an electron and an antineutrino), which increases the number of protons in the nucleus.

Section 30882
Exam code: quiz07f3yN
(A) : 1 student
(B) : 6 students
(C) : 3 students
(D) : 0 students
(E) : 0 students
(F) : 22 students
(G) : 0 students

Success level: 69%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.21

Physics quiz archive: radioactive decay, Feynman diagrams

Physics 205B Quiz 7, spring semester 2013
Cuesta College, San Luis Obispo, CA
Section 30882, version 1
Exam code: quiz07f3yN

Section 30882 results

0- 6 :	** [low = 0]
7-12 :	****
13-18 :	************* [mean = 18.4 +/- 7.2]
19-24 :	*****
25-30 :	******** [high = 30]

20130520

Astronomy current events question: pear-shaped nuclei

Astronomy 210L, spring semester 2013
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!)

Nicole Casal Moore, "Exotic Atoms Hold Clues to Unsolved Physics Puzzle at the Dawn of the Universe," May 8, 2013
http://www.ns.umich.edu/new/releases/21453-exotic-atoms-hold-clues-to-unsolved-physics-puzzle-at-the-dawn-of-the-universe

An international team of physicists found evidence for pear-shaped nuclei, which may explain why the universe:
(A) is expanding.
(B) does not have flat spacetime.
(C) does not have wormholes.
(D) has life that is carbon-based.
(E) has more matter than antimatter.

Correct answer: (E)

Student responses
Sections 30682
(A) : 3 students
(B) : 1 student
(C) : 0 students
(D) : 1 student
(E) : 17 students

Astronomy current events question: white dwarfs polluted by asteroid-like infall

NASA press release, "NASA's Hubble Space Telescope Finds Dead Stars Polluted with Planet Debris," May 9, 2013
http://www.nasa.gov/mission_pages/hubble/science/hyades-dwarf.html

NASA's Hubble Space Telescope observed __________, which may be evidence that white dwarfs are being polluted by asteroid-like debris falling onto them:
(A) silicon and carbon in white dwarfs' atmospheres.
(B) numerous transits across white dwarfs.
(C) decreasing white dwarf fusion rates.
(D) strong wobbles in white dwarf positions.
(E) increasing white dwarf masses.

Correct answer: (A)

Student responses
Sections 30682
(A) : 11 students
(B) : 4 students
(C) : 1 student
(D) : 1 student
(E) : 5 students

Astronomy current events question: source of water on Earth and the moon

Kelly Beatty, "Earth and Moon: Sharing a Drink," May 9, 2013
http://www.skyandtelescope.com/community/skyblog/newsblog/Earth-and-Moon-Sharing-a-Drink-206859621.html

Brown University researchers determined that asteroids may have provided most of the water on both Earth and the moon by analyzing traces of water trapped in:
(A) orbit between Earth and the moon.
(B) the moon's polar craters.
(C) volcanic rocks from the moon.
(D) the moon's core.
(E) astronaut spacesuit boots.

Correct answer: (C)

Student responses
Sections 30682
(A) : 0 students
(B) : 4 students
(C) : 17 students
(D) : 0 students
(E) : 0 students

Astronomy quiz question: comparative surface dating of terrestrial planets

Astronomy 210 Quiz 7, spring semester 2013
Cuesta College, San Luis Obispo, CA

__________ are used to compare the age of different regions on terrestrial planets.
(A) Impact crater densities.
(B) Infrared measurements.
(C) Volcano heat maps.
(D) Polar ice caps.

Correct answer (highlight to unhide): (A)

Because of the rate of bombardment in the solar system has decreased over time, the density of impact craters indicates the surface age of a terrestrial planet, where a heavily cratered region is relatively older than a smoother region, which would have experience more recent geological activity.

Section 36074
Exam code: quiz07n0iC
(A) : 20 students
(B) : 3 students
(C) : 2 students
(D) : 1 student

Success level: 79% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.57

Section 30676
Exam code: quiz07sEcn
(A) : 27 students
(B) : 9 students
(C) : 2 students
(D) : 4 students
(No response) : 1 student

Success level: 66% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.54

Astronomy quiz archive: solar system

Astronomy 210 Quiz 7, spring semester 2013
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz07n4IA

Section 30674

0- 8.0 :
8.5-16.0 :	**** [low = 10.0]
16.5-24.0 :	*******
24.5-32.0 :	********** [mean = 24.1 +/- 7.9]
32.5-40.0 :	***** [high = 36.5]

Section 30676, version 1
Exam code: quiz07Sw0r

Section 30676

0- 8.0 :	***** [low = 7.0]
8.5-16.0 :	*********
16.5-24.0 :	********************** [mean = 18.2 +/- 6.5]
24.5-32.0 :	*****
32.5-40.0 :	** [high = 36.0]

20130514

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

Astronomy 210, spring semester 2013
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.

"It was interesting to read that the possibility of life on another planet isn't just science-fiction."

"Even though I'm really afraid of life outside of Earth, it's still interesting to learn about."

"The origin of life; 'nuff said, extremely interesting."

"The Drake equation."

"DNA and the code of life."

"Evolution really intrigues me, I'm absolutely fascinated by the factors of the slow development of life up until when the human race began, then I get lost. I say that because I used to watch the show Ancient Aliens before before realizing I should just question everything they "teach" you on the History Channel. And there are so many theories as to how we developed into such a perfectly-structured form of life but the idea that other life off this planet came to increase our development seems plausible lol."

"I found the definition of a living thing interesting because when it's put into terms such as must be able to manipulate it's environment then you realize that, that really is what all living things do, and not just things."

"How much time and energy is spent trying to find extraterrestrial intelligence, it is not something I have really given much thought to other than when my brother tries to freak me out telling me aliens are real and whatnot."

"How we all started from single cells and ended up here today."

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

"I don't think I could ever solve the Drake equation, even if I tried."

"I found the Drake equation confusing, I would like to see how it can be used."

"Drake equation. Why does he only multiply by the stars in our galaxy, when he should multiply by the number of galaxies in our universe as well. Life it seems would be common if you include the number habitable zones in the entire universe."

"Geologic time. It's kind of hard to understand how life existed 3.4 billion years ago but there is no evidence of simple organisms until 600 million years ago."

"The different radio telescopes and how they are trying to communicate with other civilizations. I don't really understand the range of waves that can be detected and cannot."

How important is it to you to know whether or not there may be life elsewhere other than on Earth?

Unimportant:	** [2]
Of little importance:	** [2]
Somewhat important:	***** [5]
Important:	********* [9]
Very important:	****** [6]

Briefly explain your answer regarding the importance of knowing whether there may be life elsewhere other than on Earth.

"If we can find another planet that is suitable for life we can travel to it and create another planet to call home. Also, we could use the resources from that planet."

"I am deathly afraid of aliens, so if they are out there I would very much like to know so I could build a safehouse or something."

"It's only somewhat important because we can almost create life in a lab artificially. Machines themselves are becoming more like life. We could feasibly program a robot to extract energy, maintain itself, modify its surroundings, survive, and reproduce (replicate). We could also send one of these self-replicating machines to another planet, programmed to get a city built for humans upon their later arrival."

"We need to know if there are other living things out there that may be able to help us out in the future."

"I wanna party with some aliens."

"To know that there is life other than us would be mind-blowing."

"I think if there is life outside of Earth it would be nice to know, but it wouldn't be detrimental to my sanity or anything like that."

"If there is other life out there it should be important to us because what if it can change our lives dramatically (good or bad). Knowledge is power."

"Because I believe they have already been here before and still are."

"I'm sure that there is life on other planets out of our solar system, I just want confirmation."

"It would depend on how much information we have on that life. For example if there are only plants that have life then I will be interested but not very interested. So it would depend on the context but it is still generally interesting."

"If there is any other life in the universe I would not be surprised, because the universe is massive. If there is life elsewhere I wonder what it is like."

"It's important to know whether or not there's life on somewhere else besides earth because for one, we'll know; and also maybe is life is sustained somewhere else, it could sustain us too. Earth's only temporary after all."

"Due to my overactive anxiety I think I would rather not know and be blissfully ignorant of this information."

"I'll probably be dead before any kind of evidence of extraterrestrial life arises. It would be neat if we discovered a planet that has the most chances of survival during this lifetime."

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

"P-dog do you think there are aliens?" (They're out there. Somewhere. I'd bet on it. Like, maybe a dollar.)

"In your opinion which is better: the Predator or the Alien?" (What about the Engineers? Can I choose them? Those guys were awesome, too, in their own way.)

"Do you ever wish that you could have an exciting life, but actually find a way to live it??" (Aside from Mrs. P-dog, my life is actually quite boring, thank you. P.S. Boring is good. No drama. No worries.)

20130513

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

"I really liked the 'Here is Today' diagram. It was really cool and it explained things about the century, time scales, geology and life on Earth."

"I found the origin of life to be pretty cool. That's an interesting subject to me."

"Not sure."

"It took roughly 1 billion years for life to take root on Earth."

"SWAG. Love it! Humor and humility in any community is a sign of intelligence, and knowing its proclaimed in astronomy and associated fields allows me to feel there is a high level of competency being striven for."

"I found it cool that a couple different moons can possibly support life because they all had liquid water at one point in their lives or still contain it below frozen icy crusts."

"I really enjoyed the textbook's 'afterword' and the idea that astronomy's greatest value is what it teaches us about ourselves and our own position in nature. Life is special, and intelligence is even more special. We have a responsibility to us it wisely."

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

"The Julia Child video was kind of hard to understand and to relate it to life, its building blocks and primordial soup."

"The Drake equation."

"Low-luminosity stars have small habitable zones, but massive stars having larger habitable zones would seem more likely to be able to support life, yet can't due to their short life--counterintuitive."

How important is it to you to know whether or not there may be life elsewhere other than on Earth?

Unimportant:	* [1]
Of little importance:	*** [3]
Somewhat important:	***** [5]
Important:	** [2]
Very important:	******* [7]

Briefly explain your answer regarding the importance of knowing whether there may be life elsewhere other than on Earth.

"The universe is huge, and there are billions of planets out there so there can be millions of them with life on them. Although its hard to imagine it, its a cool thought; so maybe aliens do exist."

"I think aliens or the idea of them is badass."

"I don't think about it much."

"It would be interesting to know we aren't alone."

"Well if one day Earth dies for some reason then we can get on spaceships or something and live in another planet."

"We have enough issues of daily living to contend with, and that should be dealt with, before spending the money, resources and energy required to learn if others exist 'out there.'"

"It would be reassuring to know that life can develop in many different places. Perhaps it means mankind will be able to find another planet when the time comes. But if we are alone, we must deal with that too. Like the authors say, we have a billion years to prepare, and a billion years is a long time."

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

"What do you think about life elsewhere?" (It's out there. Somewhere. I'd bet on it. Like, maybe a dollar.)

"I have nothing to say." (I have no idea how to respond to that.)

"Are you taking a vacation this summer?" (Yes--I'm going to an astronomy education conference. To me, that is exciting.)

"When will you let us know what essay questions will be on the Final Exam?" (Last week.)

"Will we be getting the chance to do extra credit?" (Yes. Totally going to happen. Your astronomy teacher would never lie.)

"Astronomy views nature on the largest possible scale. Does this give astronomers a point of view different from other scientists?" (I would think so. Remember, unlike all of you by the end of this semester, I've never even taken an astronomy course. So I'll either ask you what you think, or maybe an astronomer at that education conference.)

"Are you a person of: faith? Science? Both?" (Yes, yes, and yes.)

"I'm sad this class is almost over. I will definitely be taking the lab! (I'm sad, too. See you in lab soon enough.)

Astronomy current events question: VLA detecting distant galaxy radio sources

Dave Finley, "VLA Gives Deep, Detailed Image of Distant Universe," April 30, 2013
http://www.nrao.edu/pr/2013/vladeep/

Astronomers using data from the Very Large Array radio telescopes determined that background radio emissions from distant galaxies are mainly from:
(A) massive central black holes.
(B) dark matter.
(C) dark energy.
(D) very cold hydrogen clouds.
(E) gravity waves.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 12 students
(B) : 10 students
(C) : 1 student
(D) : 1 student
(E) : 7 students

Astronomy current events question: renaming asteroid (101955) 1999 RQ36

Dwayne Brown and Nancy Neal Jones, "NASA Spacecraft Will Visit Asteroid with New Name," May 1, 2013
http://www.nasa.gov/home/hqnews/2013/may/HQ_13-128_OSIRIS-Rex_Asteroid.html

A third-grade student won a contest to __________ an asteroid to be explored by NASA's OSIRIS-REx spacecraft.
(A) send Facebook messages from.
(B) keep a sample from.
(C) claim mineral rights for.
(D) rename.
(E) be the official spokesperson for.

Correct answer: (D)

Student responses
Sections 30678, 30679, 30680
(A) : 0 students
(B) : 4 students
(C) : 1 student
(D) : 25 students
(E) : 2 students

Astronomy current events question: dark matter detector bubbles

Fermilab press release, "New Dark Matter Detector Begins Search for Invisible Particles," May 2, 2013
http://www.fnal.gov/pub/presspass/press_releases/2013/Dark-Matter-Detector-2013.html

The COUPP-60 detector at the SNOLAB underground laboratory in Ontario, Canada will detect dark matter particles that produce __________ in a tank of water and fire extinguisher chemicals.
(A) bubbles.
(B) antimatter.
(C) neutrinos.
(D) radioactivity.
(E) photons.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 26 students
(B) : 1 student
(C) : 2 students
(D) : 3 students
(E) : 1 student

20130512

Online reading assignment: Feynman diagrams, quantum electrodynamics (QED)

Physics 205B, spring semester 2013
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 (re-)reading presentations on Feynman diagrams (Phillip "Flip" Tanedo, Cornell University/USLHC Collaboration) and quantum electrodynamics (QED) (Christopher "Bot" Skilbeck, cronodon.com).

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.

"At first I didn't realize how simple it was to draw these diagrams, but now I am realizing that I can do this, so it is becoming more interesting to me!"

I find it interesting that someone has found a way to explain this concept as a game."

"I don't like this section."

"I think the idea of antimatter and virtual particles is interesting."

"It is interesting how such simple diagrams can represent such a seemingly complex subject."

"It was interesting to read about the virtual particles on the QED site because it provided a better description of how and why they come in and out of existence so quickly."

"It seems interesting but I'm quite confused on what its all about."

"I find it interesting that particle physics can be explained in such a simple way."

"I really like Feynman diagrams, they make sense to me."

"I think the general motion and interaction of subatomic particles is interesting because they end up behaving in pretty funky ways and it is cool to know how those behaviors happen."

"I thought it was interesting how we were told our entire science life that unlike charges attract but after reading the article from the hw question it was a lil confusing to understand the rest of the article."

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

"I'm not sure I understand all of the different ways of drawing the electrons and photons. Is there a reason the have the angles they have? What about the drawing their directions?"

"Following the diagrams but I am getting it."

"The Feynman diagrams are confusing. the positrons moving backward in time is weird."

"I don't understand exactly what a pion is or the forces pions create."

"The virtual particles are confusing to me."

"The QED site was confusing because it broke down the simple components on neutrons and protons into deeper classifications that I just didn't understand because it's like too much information and just confused me."

"The idea of a system borrowing a lot of energy for a short period of time or a little for a long period of time...what?"

"Everything, especially the QED article."

"How can you tell if a particle is virtual or not?"

"I am still very confused on how these Feynman diagrams work. I have been trying to figure out what everything means but I just cant seem to fully grasp it."

Describe how the path of a virtual particle is drawn on a Feynman diagram.

"With a vertical photon line."

"The path of a virtual particle is drawn in between the 'incoming' and 'outgoing' side of the diagram. It is simply a particle that is so briefly in existence that it is not observed but allows the incoming particle to become the outgoing."

Describe the difference between first-order process and second-order process Feynman diagrams.

"The first order is an exchange of one photon. The second order is an exchange of two photons."

"The first-order events denote one interaction happening, while the second-order events denote two interactions happening simultaneously. Luckily, the higher order events do not take place very often in nature, so we can disregard them."

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

"Why are we using the Feynman diagrams?" (We have to end the semester with something. That something is Feynman diagrams.)

"I'm still trying to wrap my head around how a diagram can depict a spontaneous formation of an electron and a positron from a photon." (Wrap your head around these bubble chamber tracks in liquid helium, where two high-energy photons (which leave no tracks) spontaneously form electron-positron pairs, which curve in opposite directions, due to the right-hand and left-hand rule forces exerted on them by an external magnetic field.)

"Virtual particles are very confusing...they exist, but not really?" (Virtual photons emanating from a charge don't exist, unless they encounter another charge (and can borrow energy/momentum, and thus exert a force on that other charge), or if the charge is suddenly moved, leaving the virtual photons behind (creating bremsstrahlung, "braking radiation," as in your dentist's x-ray machine.)

"Can you describe annihilation, is that just when two particles become one or is it specific to what is happening at their vertex interaction?" (Yes, and yes?)

"I know the cutoff for an A is 600 points, but what happens if someone is at 595? do you ever have any leeway for grading when it comes to final grades?" (That's what extra-credit points are for.)

Astronomy midterm question: relative distances of same absolute visual magnitude, different apparent magnitude stars

Astronomy 210 Midterm 2, spring semester 2013
Cuesta College, San Luis Obispo, CA

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

admin: If two stars have the same absolute visual magnitudes, but different apparent magnitudes, how do you tell which star is farther away?
tham158: The star with the greatest difference between apparent magnitude and absolute visual magnitude is farther away.

Discuss an example (two stars with the same absolute visual magnitudes, but different apparent magnitudes) that would show that the response given by "tham158" is not correct, and how you know this. Explain using the properties of apparent magnitude, absolute visual magnitude, and distance.

[*]Adapted from alliknowisthatiknownothing.com/how-to-tell-which-star-is-farther-away-with-magnitudes-given/.

Solution and grading rubric:

p:
Correct. Understands difference between apparent magnitude (m) values and absolute magnitude (M_V) values, and that for two stars that have the same absolute magnitude (same brightness if both located 10 parsecs away) it is possible for the star with the greatest difference between m and M_V to be closer (instead of farther away) if its m is brighter than M_V. May cite examples of one star being farther and one star being closer than 10 parsecs, or two stars both closer than 10 parsecs.
r:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. As (p), but example may use stars that do not have the same M_V.
t:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Some serious attempt at a contrary argument or example where the star with the greater difference between m and M_V would be closer.
v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use relations between d, m, and M_V somehow.
x:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on apparent magnitudes, absolute magnitudes, and distances.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Section 30674
Exam code: midterm02nNm3
p: 6 students
r: 3 students
t: 6 students
v: 16 students
x: 0 students
y: 0 students
z: 0 students

Section 30676
Exam code: midterm02s5Sz
p: 9 students
r: 4 students
t: 6 students
v: 24 students
x: 0 students
y: 1 student
z: 0 students

A sample "p" response (from student 2981), discussing two stars with the same absolute visual magnitudes:

A sample "r" response (from student 1022), discussing two stars with different absolute visual magnitudes:

20130511

Astronomy midterm question: star cluster with supergiants and white dwarfs?

Astronomy 210 Midterm 2, spring semester 2013
Cuesta College, San Luis Obispo, CA

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

Pd: Would a star cluster with both supergiants and white dwarfs be old, or young?
t153: It would certainly be very unlikely for any cluster to have both supergiants and white dwarfs.

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=20130419183134AAKacCx.

Solution and grading rubric:

p:
Correct. Understands that:
1. stars in the same cluster are all born at the same time;
2. massive stars evolve faster than medium-mass stars;
3. 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:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Discusses only two out of the three concepts in (p) correctly. 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:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Discusses only one out of three concepts in (p) correctly, typically 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 30674
Exam code: midterm02nNm3
p: 3 students
r: 14 students
t: 4 students
v: 3 students
x: 7 students
y: 0 students
z: 0 students

Section 30676
Exam code: midterm02s5Sz
p: 4 students
r: 29 students
t: 6 students
v: 1 student
x: 4 students
y: 0 students
z: 0 students

A sample "p" response (from student 1127):

Another sample "p" response (from student 7045):

Physics midterm question: same charge, same gap, different area capacitors

Physics 205B Midterm 2, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Comprehensive Problem 17.109

Two parallel plate capacitors have different areas, but the same separation gaps and the same charge. Discuss  why the smaller area capacitor stores more electric potential energy. Explain your reasoning using the properties of capacitors.

Solution and grading rubric:

p:
Correct. (1) As capacitance is proportional to plate area (with the same separation distance for both capacitors), the smaller area for the first capacitor means that has a smaller capacitance. (2) The two capacitors have the same charge stored on them, so the first capacitor with a smaller capacitance must have a larger potential difference. (3) Using electric potential energy U_E = (1/2)∙Q∙(ΔV), the first capacitor with the greater potential difference stores more electric potential energy.
r:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Two of the three arguments in (p) are correct and complete.
t:
Nearly correct, but argument has conceptual errors, or is incomplete. Only one of the three arguments in (p) are correct and complete.
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.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 30882
Exam code: midterm02w1Ig
p: 18 students
r: 8 students
t: 6 students
v: 1 student
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 4444):

Physics midterm question: 240 V light bulb in 120 V socket

Physics 205B Midterm 2, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 22.45

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

Would a 25 W light bulb (for a 240 V socket) be dimmer in a 120 V socket?
Yes, but you get a lot less than half the light, even though the applied voltage is half the rated voltage.

Discuss why this answer is correct, and how you know this. Explain your reasoning using the properties of currents and potential differences, and Kirchhoff's rules and Ohm's law.

[*] wiki.answers.com/Q/Can_a_240V_lightbulb_25W_work_in_a_120V_socket_and_would_it_just_be_dimmer.

Solution and grading rubric:

p:
Correct. Applies Ohm's law and/or power equations, keeping the resistance the same to determine that the light bulb in the 120 V socket would use one-quarter of the power in the 240 V socket.
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. Finds different resistances for light bulb, based on power being the same in either socket.
x:
Implementation/application of ideas, but credit given for effort rather than merit.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Sections 30882
Exam code: midterm02w1Ig
p: 8 students
r: 3 students
t: 6 students
v: 16 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1029):

Physics midterm problem: magnetic force on moving charge

Physics 205B Midterm 2, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Multiple-Choice Questions 19.1-19.4, Problem 19.19

A +6.0 nC charge moves at constant speed of 5.5×10⁴ m/s in the region between two magnets, and experiences a force of 8.5×10^–6 N. Calculate (a) the magnitude of the magnetic field  at the location of the charge, and (b) determine  the direction of the magnetic force on the +6.0 nC  charge. Show your work and explain your  reasoning.

Solution and grading rubric:

p:
Correct. Determines magnitude of magnetic field at the location of the charge, where the angle θ between velocity v and the magnetic field B is 45°; and the direction of the force on the moving charge from right-hand rule 1.
r:
Nearly correct, but includes minor math errors. Magnitude incorrect (typically from using θ = 90°); or direction of right-hand rule incorrect.
t:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Magnitude incorrect (typically θ = 90°), and direction of right-hand rule incorrect.
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 30882
Exam code: midterm02w1Ig
p: 10 students
r: 12 students
t: 7 students
v: 4 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 7187):

20130507

Online reading assignment: runaway planets, jovian planets, and dwarf planets (oh my!) (SLO campus)

Astronomy 210, spring semester 2013
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 runaway planets (Venus and Mars), jovian planets (Jupiter, Saturn, Uranus and Neptune), and dwarf planets (and the International Astronomy Union classification scheme).

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.

"It was interesting to see what classified a planet as a planet or non-planet--bring Pluto back."

"Everything."

"I found the two types of volcanoes on Venus and Mars interesting because in some ways they are similar to Earth's but then they also have very big differences than the ones on Earth."

"Reading about Venus and Mars was interesting. You always hear about these two planets, since they're the closest, but I never really knew too much about them . I didn't know the stripes on Jupiter and Saturn were clouds."

"How the mass of the planet affects greenhouse gases, I didn't know much about greenhouse gases to start."

"Venus was once very similar to the conditions of earth but being closer to the sun, its water evaporated and it became a lot warmer from a stronger greenhouse effect also adding to its dense atmosphere."

"I liked seeing the Mars video and how each frame was a sol from the actual rover cam--that's way cool."

"I found Venus interesting because I assumed that Venus was a cold planet but it's actually hot."

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

"Why is Pluto not a planet?"

"Why does the interior of Neptune appear to be a higher temperature then Uranus, when it is roughly the same size, composition, but farther away from the sun?"

"I don't know what information I should be specifically looking out for about each planet."

"How do they know exactly how the surface of Venus looks like when the atmosphere doesn't allow things through?"

"Nothing really stood out to be confusing most concepts seemed to be straightforward. Keeping all the planets in order and not confusing on with an other may be a challenge though."

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

"I've been overstressed and busy, I apologize that school has had to become a second on the list. But it is only temporary. You're a great teacher, I have and still think that." (Word.)

"Will the essay questions on the final be the same ones from our previous two midterms?" (No.)

"Are our three lowest quiz grades already dropped from our point values for the summary in this class?" (Out of the eight quizzes this semester, you keep your five highest scores, and drop your lowest three scores. Since you've only taken six quizzes so far, you kept your five highest scores so far, and dropped your one lowest quiz score so far.)

Astronomy current events question: Earth's core hotter than previously modeled

Sebastian Anthony, "Earth's Core Is Much Hotter than Previously Thought--Hotter than the Surface of the Sun," April 26, 2013
http://www.extremetech.com/extreme/154357-earths-core-is-much-hotter-than-previously-thought-hotter-than-the-surface-of-the-sun

French researchers revised higher estimates of Earth's core temperature based on measuring the properties of iron:
(A) from micrometeorites.
(B) produced in the sun's core.
(C) squeezed between two diamonds.
(D) in volcanic calderas.
(E) placed in experimental fusion reactors.

Correct answer: (C)

Student responses
Sections 30678, 30679, 30680
(A) : 3 students
(B) : 7 students
(C) : 19 students
(D) : 9 students
(E) : 12 students