P-dog's blog: boring but important: 201011

20101130

Astronomy midterm question: no center for universe?

Astronomy 210 Midterm 2, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

[20 points.] An astronomy question on an online discussion board (http://answers.yahoo.com/question/index?qid=20100905145749AAyQLJr) was asked and answered:

Bell: What is at the center of the universe?

Stimpy: The universe is not defined to have [a] center. Wherever you are in the universe you will always appear to be in the center.

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

Solution and grading rubric:

p = 20/20:
Correct. Hubble's law is that the recession velocity of galaxies is proportional to distance, evidence is that there is a greater redshift of absorption lines for distant galaxies compared to nearby galaxies. This corresponds to the expansion of space between galaxies, such that each galaxy seems to be center of expansion as observed from their position. May use analogies as not-like-an-explosion, raisin bread, enlargement of between-spaces, etc.
r = 16/20:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Discusses how Hubble's law expansion will be observed identically for all viewpoints, but does not explicitly discuss absorption line redshift evidence for Hubble's law.
t = 12/20:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Describes how Hubble's law expansion will be observed identically for all viewpoints, but Hubble's law discussion is problematic or incomplete.
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.
y = 2/20:
Irrelevant discussion/effectively blank.
z = 0/20:
Blank.

Grading distribution:
Section 70160
p: 11 students
r: 10 students
t: 11 students
v: 5 students
x: 3 students
y: 1 student
z: 0 students

A sample "r" response (from student 2421):

20101129

Astronomy midterm question: monolithic collapse model

Astronomy 210 Midterm 2, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

[20 points.] Discuss the evidence for the monolithic collapse model of the Milky Way (spherical gas cloud flattening into a disk). Support your answer using the orbit and metal content properties of halo stars versus disk stars.

Solution and grading rubric:

p = 20/20:
Correct. Discusses evidence supporting the flattening of the Milky Way's shape by explaining how metal content increases for younger generations of stars, and observations that disk stars are metal-rich compared to the metal-poor halo stars above and below the disk.
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 some discussion related to the monolothic collapse model.
x = 4/20:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion unrelated to the monolithic collapse model.
y = 2/20: Irrelevant discussion/effectively blank.
y = 2/20:
Irrelevant discussion/effectively blank.
z = 0/20:
Blank.

Grading distribution:
Section 70160
p: 17 students
r: 8 students
t: 4 students
v: 6 students
x: 3 students
y: 3 students
z: 0 students

A sample "p" response (from student 1991):

20101128

Astronomy midterm question: same size supergiant and giant stars

Astronomy 210 Midterm 2, fall semester 2010
Cuesta College, San Luis Obispo, CA

Discuss whether or not a supergiant and a giant star with the same size could have the same temperature, and why. Support your answer using the Stefan-Boltzmann law and/or an H-R diagram.

Solution and grading rubric:

p:
Correct. Uses either the H-R diagram and/or the Stefan-Boltzmann law to show that since all supergiants are more luminous than giants, then it is not possible for a supergiant and a giant to have the same size and same temperature (as that would result in the same luminosity).
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. Attempts to use H-R diagram and/or Stefan-Boltzman law with stars of same size and same temperature, while realizing that supergiants and giants have different luminosities, but does not adequately resolve that these two arguments are inconsistent with each other (or resolves this with a plausible overlapping range of sizes/temperatures).
v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use H-R diagram and/or Stefan-Boltzman law.
x:
Implementation/application of ideas, but credit given for effort rather than merit.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Section 70160
p: 21 students
r: 7 students
t: 6 students
v: 7 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1204):

Another sample "p" response (from student 0002):

20101127

Physics midterm problem: total magnetic field of two current-carrying wires

Physics 205B Midterm 2, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 19.61

[20 points.] Two long straight wires carry different amounts of current in the plane of this page. Determine the direction and magnitude of the magnetic field at the location indicated. Show your work and explain your reasoning.

Solution and grading rubric:

p = 20/20:
Correct. Determines directions of the magnetic fields of each current separately at point P, where B_1 points into the page, and B_2 points out of the page. Finds the magnitudes of these magnetic fields, and since B_2 has a greater magnitude than B_1, the resulting total magnetic field at point P will point out of the page, with a (positive definite) magnitude that is the arithmetic difference of the two magnitudes.
r = 16/20:
Nearly correct, but includes minor math errors. Direction or magnitude of total magnetic field has minor error.
t = 12/20:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Both direction and magnitude of total magnetic field have minor errors.
v = 8/20:
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner.
x = 4/20:
Implementation of ideas, but credit given for effort rather than merit.
y = 2/20:
Irrelevant discussion/effectively blank.
z = 0/20:
Blank.

Grading distribution:
Section 70856
p: 8 students
r: 1 student
t: 2 students
v: 0 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 8110):

20101126

Physics midterm problem: light bulb power dissipation in circuit

Physics 205B Midterm 2, fall semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 18.63

An ideal 16.0 V emf source is connected to ideal light bulbs and an ideal resistor, as shown at right. Find the amounts of power used by each light bulb. Show your work and explain your reasoning using Kirchhoff's rules, Ohm's law, and electric power.

Solution and grading rubric:

p:
Correct. Determines power of 8.0 Ω light bulb by direct application of P = (∆V)²/R, or first solves for I through light bulb, and then uses P = I·∆V or I²·R. For the 5.0 Ω light bulb, must first solve for the current passing through the lower loop, then uses power = I²·R, or uses voltage drop across the 5.0 Ω light bulb to use P = I·∆V or (∆V)²/R.
r:
Nearly correct, but includes minor math errors. Typically solves correctly for the power used by the 8.0 Ω light bulb, but has conceptual errors in applying Kirchhoff's rules and Ohm's law to determine current passing through and/or voltage drop across the 5.0 Ω light bulb.
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.
x:
Implementation of ideas, but credit given for effort rather than merit.
y:
Irrelevant discussion/effectively blank.
z:
Blank.

Grading distribution:
Section 70856
p: 7 students
r: 4 students
t: 0 students
v: 0 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1025). Note that the numerical results here are correct, but there are several errors in setting up calculations:

the equivalent resistance is set up incorrectly--it should be written R_eq = ((5.0 Ω + 4.0 Ω)^–1 + (8.0 Ω)^–1)^–1, but the resulting value is correct.
the power dissipated by the 5.0 Ω light bulb is set up incorrectly--it should be written P = I²⋅R = (1.778 A)²·(5.0 Ω), but the resulting value is correct.

A sample "r" response (from student 1010):

20101125

Found physics: turkey cooling

"...Imagine what would happen if you took a Thanksgiving turkey piping hot from the oven and immediately placed it in a freezer. (Consider a perfect freezer--one that can remove heat instantly and always stay at its set temperature.) Initially the turkey would be at the same temperature throughout (assuming that you had roasted it for sufficiently long). Only a very thin skin would immediately take on the temperature of the freezer. But soon, the outer layers of turkey meat would cool as heat diffused outward, even though the center retained its initial oven-like temperature. Eventually, of course, everything including the stuffing would cool off; that is, the temperature inside your turkey would depend both on the distance from the surface and on the time elapsed since you placed it in the freezer."
--Philip C. England, Peter Molnar, and Frank M. Richter, "Kelvin, Perry and the Age of the Earth," American Scientist, volume 95 number 4, p. 342 (2007)

The "Turkey/Cornish Hen Effect".

Related posts:

Bergman's Rule (wikipedia.org).

Allen's Rule (wikipedia.org).

20101123

Astronomy current events question: Milky Way bubbles

Astronomy 210L, Fall Semester 2010
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!)

Kelly Beatty, "Why is the Milky Way Blowing Bubbles?," November 11, 2010
http://www.skyandtelescope.com/community/skyblog/newsblog/107302599.html

Images of __________ above and below the Milky Way have been extracted from NASA Fermi Large Area Telescope data.
(A) dark matter.
(B) antimatter vortexes.
(C) disrupted dwarf galaxies.
(D) rogue black holes.
(E) gamma-ray bubbles.

Correct answer: (E)

Student responses
Sections 70178, 70186, 70200
(A) : 6 students
(B) : 1 student
(C) : 8 students
(D) : 2 students
(E) : 46 students

Astronomy current events question: gas-powered comet jets

Astronomy.com editors, "Primordial Dry Ice Fuels Comet Jets," November 11, 2010
http://astronomy.com/en/News-Observing/News/2010/11/Cometary%20dry%20ice%20jet%20fuel.aspx

The NASA EPOXI spacecraft observed jets of gas and particles powered by __________ bursting from Comet 103P/Hartley 2.
(A) oxygen.
(B) water vapor.
(C) nitrogen.
(D) carbon dioxide.
(E) methane.

Correct answer: (D)

Student responses
Sections 70178, 70186, 70200
(A) : 0 students
(B) : 9 students
(C) : 10 students
(D) : 43 students
(E) : 2 students

Astronomy current events question: Eris vs. Pluto

Kelly Beatty, "Eris Gets Dwarfed (Is Pluto Bigger?)," November 7, 2010
http://www.skyandtelescope.com/news/106861063.html

Astronomers in Chile recently observed dwarf planet Eris __________, which may indicate that it is slightly smaller than dwarf planet Pluto.
(A) passing in front of a star.
(B) during a continent-wide power outage.
(C) eclipsed by Pluto.
(D) using infrared and radio waves.
(E) bombarded by an impactor.

Correct answer: (A)

Student responses
Sections 70178, 70186, 70200
(A) : 51 students
(B) : 2 students
(C) : 8 students
(D) : 2 students
(E) : 1 student

20101118

Cuesta College North County campus star party

20101118775
http://www.flickr.com/photos/waiferx/5188395513/
Originally uploaded by Waifer X

Waxing gibbous moon, November 18, 2010, photographed with a hand-held Nokia e71 smartphone through an Orion SkyQuest XT8 8" reflector at Cuesta College North County Campus, Paso Robles, CA.

Sights seen:
Waxing gibbous moon
Jupiter, north equatorial belt, four Galilean satellites

20101117

Astronomy current events question: Kuiper belt object colors

Astronomy.com editors, "Kuiper Belt of Many Colors," November 1, 2010
http://astronomy.com/News-Observing/News/2010/11/Kuiper%20Belt%20of%20many%20colors.aspx

Scientists from NASA's Goddard Space Flight Center have proposed that the many different colors of Kuiper belt objects may come from:
(A) different layers exposed by the sun.
(B) tidal heating.
(C) sulfur-rich volcanoes and geysers.
(D) radioactive decays.
(E) simple organisms similar to algae or lichen.

Correct answer: (A)

Student responses
Sections 70178, 70186, 70200
(A) : 32 students
(B) : 3 students
(C) : 1 student
(D) : 3 students
(E) : 5 students

Astronomy current events question: EPOXI spacecraft previous mission

Astronomy.com editors, "Deep Impact Flyby Spacecraft Images Comet 103P/Hartley," November 4, 2010
http://astronomy.com/en/News-Observing/News/2010/11/Deep%20Impact%20Flyby%20spacecraft%20images%20Comet%20103P%20Hartley.aspx

Before flying past Comet 103P/Hartley 2, the NASA EPOXI spacecraft was originally called the Deep Impact spacecraft, which had successfully completed its mission of:
(A) returning samples from a dark nebula.
(B) shooting a projectile into the nucleus of another comet.
(C) flying through the asteroid belt.
(D) surveying the moon's surface for traces of water.
(E) tracking and deflecting a potential asteroid impactor.

Correct answer: (B)

Student responses
Sections 70178, 70186, 70200
(A) : 1 student
(B) : 31 students
(C) : 4 students
(D) : 3 students
(E) : 5 students

Astronomy current events question: Saturn ring debris mountains

Annalee Newitz, "Two-Mile-High Mountains Discovered in Saturn's Rings," November 1, 2010
http://io9.com/5678790/two+mile+high-mountains-discovered-in-saturns-rings?skyline=true&s=i

The NASA Cassini spacecraft has recently imaged __________ in Saturn's rings, which may be caused by gravitational fluctuations between Saturn and its moons.
(A) snow cyclones.
(B) debris mountains.
(C) spiral arms.
(D) moonlet formation.
(E) liquid nitrogen geysers.

Correct answer: (B)

Student responses
Sections 70178, 70186, 70200
(A) : 0 students
(B) : 39 students
(C) : 2 students
(D) : 1 student
(E) : 1 student

20101107

Astronomy current events question: subsurface water on Mars

Guy Webster & Dwayne Brown, "NASA Trapped Mars Rover Finds Evidence of Subsurface Water," October 23, 2010
http://www.nasa.gov/mission_pages/mer/news/mer20101028.html

NASA's Mars Exploration Rover Spirit detected __________, which may be evidence for subsurface water on Mars.
(A) evaporated puddles.
(B) small and steady Marsquakes.
(C) permafrost.
(D) fossilized quicksand.
(E) different composition soil layers.

Correct answer: (B)

Student responses
Sections 70178, 70186, 70200
(A) : 12 students
(B) : 0 students
(C) : 16 students
(D) : 2 students
(E) : 34 students

Astronomy current events question: spiral galaxies in infrared light

Astronomy.com editors, "Spiral Galaxies Stripped Bare," October 28, 2010
http://astronomy.com/en/News-Observing/News/2010/10/Spiral%20galaxies%20stripped%20bare.aspx

The European Southern Observatory’s (ESO) Very Large Telescope (VLT) HAWK-I camera images spiral galaxies using infrared light, which is:
(A) not affected by spiral arm dust.
(B) not affected by dark matter.
(C) not affected by local light pollution.
(D) arriving at Earth just before the galaxies collided.
(E) slower and steadier than visible light.

Correct answer: (A)

Student responses
Sections 70178, 70186, 70200
(A) : 45 students
(B) : 6 students
(C) : 11 students
(D) : 1 student
(E) : 2 students

Astronomy current events question: Large Binocular Telescope Interferometer

Tom Beal, The Arizona Daily Star, "Graham Scope Has Both Eyes Open," October 23, 2010
http://www.skyandtelescope.com/news/wires?id=151393738&c=y

The Large Binocular Telescope Interferometer uses infrared light combined from two 8.4-meter mirrors in order to detect the presence of:
(A) distant star parallaxes.
(B) Earth-like planets.
(C) previously unseen spiral galaxies.
(D) near-Earth orbit asteroids.
(E) close binary star systems.

Correct answer: (B)

Student responses
Sections 70178, 70186, 70200
(A) : 5 students
(B) : 48 students
(C) : 9 students
(D) : 4 students
(E) : 4 students

20101105

Overheard: extent of Milky Way

Astronomy 210, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

(Overheard following an introductory astronomy lecture-tutorial on the total vs. visible extent of the Milky Way.)

Instructor (to class): "So why do you think we can't see most of our Milky Way?"

Student 1: "Because it's so huge."

Instructor: "Then how it is possible that we can see distant galaxies outside the Milky Way?"

(Beat.)

Student 2: "Uh...because they're huge, too?"

20101101

Astronomy current events question: Moon south pole frozen water

University of Arizona-Tucson press release, Astronomy.com editors, "It's Cold and Wet at the Moon's South Pole?," October 22, 2010
http://www.astronomy.com/en/News-Observing/News/2010/10/It%20is%20cold%20and%20wet%20at%20the%20Moons%20south%20pole.aspx

By collecting neutrons from the moon's surface, the NASA Lunar Reconnaissance Orbiter observed evidence of:
(A) solar flare damage.
(B) helium-3 and other potential fusion fuels.
(C) moonquakes.
(D) radioactivity.
(E) frozen water.

Correct answer: (E)

Student responses
Sections 70178, 70186, 70200
(A) : 1 student
(B) : 5 students
(C) : 1 student
(D) : 1 student
(E) : 52 students

Astronomy current events question: planet OGLE-TR-113b orbit shrinking

Kelly Beatty, "Watching a Planet's Death Spiral?," October 12, 2010
http://www.skyandtelescope.com/news/104782104.html

__________ is evidence that the orbit of planet OGLE-TR-113b is shrinking.
(A) Timing of its transits.
(B) Infrared observations of its hot spot.
(C) Tidal locking.
(D) A massive, yet-unseen companion.
(E) Exchange of tidal energy.

Correct answer: (A)

Student responses
Sections 70178, 70186, 70200
(A) : 25 students
(B) : 6 students
(C) : 4 students
(D) : 2 student
(E) : 14 students

Astronomy current events question: upsilon Andromeda b hot spot

Whitney Clavin, "Astronomers Find Weird, Warm Spot on an Exoplanet," October 19, 2010
http://www.nasa.gov/mission_pages/spitzer/news/spitzer20101019.html

The side of the planet upsilon Andromeda b that always faces its star is unusual because it is:
(A) experiencing a perpetual sunset.
(B) potentially habitable.
(C) not the hottest side of the planet.
(D) geologically dead.
(E) lacking water, methane, carbon dioxide and carbon monoxide.

Correct answer: (C)

Student responses
Sections 70178, 70186, 70200
(A) : 4 students
(B) : 2 students
(C) : 50 students
(D) : 1 student
(E) : 1 student

P-dog's blog: boring but important