Astronomy current events question: martian ice age gullies

Astronomy 210L, spring semester 2015
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!)

Kevin Stacey, "Gully Patterns Document Martian Climate Cycles" (January 28, 2015)
https://news.brown.edu/articles/2015/01/gullies

Gully-like features in Martian impact craters may be evidence of __________ in Mars' past.
(A) rainforests.
(B) sporadic magma flows.
(C) weaker sandstorms.
(D) several ice ages.
(E) marsquake avalanches.

Correct answer: (D)

Student responses
Sections 30678, 30679, 30680
(A) : 1 student
(B) : 3 students
(C) : 2 students
(D) : 44 students
(E) : 0 students

Astronomy current events question: confirmation of dark matter-dominated dwarf galaxy

Astronomy 210L, spring semester 2015
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!)

Susan Gawlowicz, "Lifting the Veil on a Dark Galaxy: Findings Validate Earlier Prediction of Galaxy’s Location," (February 6, 2015)
http://www.rit.edu/news/story.php?id=51213

Cepheid variable stars observed near our Milky Way galaxy confirmed the location of a previously predicted dwarf galaxy:
(A) composed of antimatter.
(B) ejected from the Milky Way.
(C) on a collision course.
(D) dominated by dark matter.
(E) with no central supermassive black hole.

Correct answer: (D)

Student responses
Sections 30678, 30679, 30680
(A) : 3 students
(B) : 7 students
(C) : 3 students
(D) : 37 students
(E) : 0 students

Astronomy current events question: VISTA's clear vista

Astronomy 210L, spring semester 2015
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!)

Richard Hook, "VISTA Stares Right Through the Milky Way," (February 4, 2015)
http://www.eso.org/public/usa/news/eso1504/

Stars beyond our Milky Way galaxy's central bulge were imaged by the European Southern Observatory VISTA telescope using infrared light, which is unaffected by:
(A) the central supermassive black hole.
(B) solar winds.
(C) dark matter.
(D) look-back time.
(E) thick dust clouds.

Correct answer: (E)

Student responses
Sections 30678, 30679, 30680
(A) : 0 students
(B) : 1 student
(C) : 11 students
(D) : 2 students
(E) : 38 students

Online reading assignment: double-slit interference

Physics 205B, spring semester 2015
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 double-slit interference.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"Don't understand."

"Did not read."

"With double slit interference, the source phase differences don't matter, just path differences, such as how much longer the wave from one source travels than the wave from the other source."

"Light from a single narrow slit spreads out primarily in directions perpendicular to the slit. Two narrow slits on the same screen interfere with one another."

"I understand what the path difference is and how to find it."

"I didn't really know (or even think about it) before, but now I know realize that there is a difference in distances that can effect the interference."

"How much longer the waves travel along the longer path (on the same path with phase differences) is given by ∆l = dsinθ. Then once you have figure out the difference in paths of the two waves you figure out if the wave interferance is constructive (maxima) or destructive (minima)."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I'm still lost on double slit interference. How is it that we can have constructive and destructive waves if we have the same two sources?"

"Probably everything, as usual."

"Basically everything besides the two equations and the situations in which they are each used for. In all honesty, I'm sufficiently lost on this particular section. I know that this builds on the constructive and destructive interference information, but I'm lost on how it does so."

"No comment."

"Seems fairly straightforward."

Explain the difference between "maxima" and "minima" in double-slit interference.

"Maximas and minimas are intensities which differ due to the interferences it undergoes. Maxima intensity is produced by constructive interference and minima intensity is produced by destructive interference."

"The maxima occurs when there is a constructive interference or when the path difference is a multiple of the wavelength. A minima occurs when there is a destructive interference or when the path difference is an odd number of half wavelengths."

"Maxima is large and minima is small."

Match the double-slit parameter with its symbol. (Only correct responses shown.)

Distance between slits: d [74%]
Any positive or negative whole number: m [71%]
Distance from slits to a projection screen: D [54%]
Wavelength of light passing through both slits: λ [80%]
Difference in paths for light passing through both slits: d·sinθ [66%]
Position along screen, as measured from the centerline: x [54%]

As defined for double-slit interference, the range for possible θ angles is:

–180° to +180°.	** [2]
–90° to +90°.	********************* [21]
0° to 180°.	****** [6]
l0° to 360°.	* [1]
(Unsure/lost/guessing/help!)	***** [5]

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

"How do you recommend we study in order to succeed on the upcoming quiz on Monday?" We'll have a practice quiz (taken from last year's class), and that should tell you what you need to focus between now and Monday.)

"I don't see or understand the point of the double slit idea yet."

"Please go over the variables more in-depth and what they really mean." (We'll do that as we go over examples in class, and highlight some technical details you'll encounter in next week's laboratory.)

"Good grief I am so confused. I would have never thought this concept so far in class would be so hard. You are the smartest man I know to understand this." (I'm still having to learn a lot about physics education research (a relatively new field), in order to understand how to better teach this stuff.)

"This has nothing to do with this week's reading assignment, but can you please clarify what the focal point is? And how there is a primary and a secondary focal point?" (For a converging lens, its primary focal point is where incoming parallel light rays are brought together and eventually meet. For a diverging lens, its primary focal point is where incoming parallel light rays appear to spread out away from. The secondary focal points are because lenses are symmetric, so there must be another corresponding focal point spaced out equally on other side.)

"So...we're almost halfway through the semester." (Shh--don't rush it. This is week six, and there are 17-18 weeks in a semester.)

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

Astronomy 210, spring semester 2015
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 the 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.

"The progression of Venus' atmosphere was quite interesting, and also a bit scary. The fact that the runaway greenhouse effect is something that could happen to Earth means we should study Venus and its atmosphere more."

"That Saturn and Jupiter have storms. I never thought about it before how other planets have mother nature effects like Earth."

"I found the surfaces of Mars and Venus to be interesting in how different, yet both inhospitable they are."

"The reason why Mercury doesn't have tectonic plates is because it cooled too quickly. It's a 'one-plate' planet like the moon--that's a comparison I'll remember."

"I had no idea that mars was so cold compared to Earth and venus. To me since it looks like a desert I imagined it would be too hot for human life, but actually it is the opposite."

"That we are almost the same size as Venus! Also that we used to think it had oceans and might have even been a 'tropical paradise.'"

"I finally understand why Pluto isn't classified as a planet."

"The jovian worlds, because they are so foreign to Earth's properties."

"The criteria for a planet--originally I thought it had everything to do with size, but turns out there are a lot of other factors that go into what defines a planet and what doesn't."

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

"How all the planets differ, why there are some gas planets and others are solid."

"How the atmosphere for a planet is retained. This is because it would make sense to me that the closer to the sun, the less gravity a planet would have since the sun would have the greatest gravity pulling away from the inner planets' atmosphere? Or that's what would make sense to me, so this is confusing to me."

"Almost everything because it is so foreign to us. Its hard to grasp the properties of other worlds."

"The 'runaway greenhouse.'"

"A planet's core heat--because how do you know the core temperature you can't stick a thermometer into it?"

Identify the relative amounts of these characteristics for Venus, compared to Earth. (Only correct responses shown.)

Interior core heat, today: about the same as Earth [26%]
Geologic activity, today: less than Earth [56%]
Volcanic outgassing, up until now: about the same as Earth [40%]
Heat from the sun: more than Earth [88%]
Amount of atmosphere, today: more than Earth [77%]

Identify the relative amounts of these characteristics for Mars, compared to Earth. (Only correct responses shown.)

Interior core heat, today: less than Earth [84%]
Geologic activity, today: less than Earth [84%]
Volcanic outgassing, up until now: less than Earth [58%]
Heat from the sun: less than Earth [70%]
Amount of atmosphere, today: less than Earth [84%]

Which jovian planet has the coolest interior temperatures?

Jupiter (most massive).	*** [3]
Saturn (most prominent rings).	* [1]
Uranus (least active weather patterns).	****************** [18]
Neptune (farthest from the sun).	******************** [20]
(Unsure/guessing/lost/help!)	* [1]

I believe Pluto should be a planet.

Strongly disagree.	** [2]
Disagree.	************* [13]
Neutral.	*************** [15]
Agree.	********** [10]
Strongly Agree.	*** [3]

Briefly explain your answer to the previous question (whether Pluto should be a planet).

"Pluto should be a planet because I grew up with it as a planet and it was my favorite due to the fact that Mickey Mouse's dog was named Pluto."

"It is not a planet because it is located in the Kuiper belt, and it is not massive enough to clear out other bodies in and near its orbit."

"Growing up I always believed Pluto was a planet, so to be honest I was highly disappointed when it was declared a dwarf planet. I looked at Pluto as the 'runt' of pack, and every one always feels bad for the runt, so they like them."

"Because Pluto is better understood as a dwarf planet. It is big enough to form a sphere but not big enough to clear out other bodies in and near its' orbit like all planets, based on definition, should be able to do."

"Up until recently, Pluto has been considered a planet and since people hate change, it might as well still be considered a planet even though it does not fit the scientific definition."

"I don't know enough information on the topic to actually make an educated decision."

"Pluto doesn't really fit in with the other eight planets, but it still fits the qualifications of being a planet."

"Although Pluto fits two of IAU's criteria for planet status, it is not large enough for it to dominate and gravitationally pull all other objects in the region into its orbit."

"I'm not sure because I'm a noob astronomer. I could go either way."

"I believe that Pluto found its relatives Eris, Ceres, Haumea, and Makemake. It is best that it shouldn't be broken up from the family of dwarf planets."

"It doesn't really concern me."

"I really don't know why it is not a planet anymore but I also don't really care."

"I feel bad for Pluto, but tough nuggets."

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

"Do you think Pluto should be a planet?" (Did we not discuss this on the first day of class? I do have strong opinions on this topic.)

"Why is Mercury a small solid rock? I thought it was closest to sun so shouldn't it be a hot volcanic planet?" (Any heat in the core, under its crust, comes from its original formation and some radioactive elements within, and not from sources the outside the planet. If Mercury were close enough to the sun such that the outside would melt, then it wouldn't be around for very long--which is what probably happened to any planets that tried to form closer to the sun than Mercury.)

"I am eating peanut M&M®s and by their shape, if they were large enough to be in the solar system, they would not be considered planets because they would not have enough gravitational pull to shape them into perfect spheres. Also the core is a peanut." (You had me at 'peanut M&M®s.')

"How scary is the midterm going to be?" (Depends. On how brave you are. Or perhaps, how unprepared.)

"What is a nebula?" (It'a a gas and dust cloud in space, and can give birth to new stars and planets. And yes, space is dirty.)

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

Astronomy 210, spring semester 2015
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 the 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.

"I am surprised that Mars has such a thin atmosphere, and that it is actually a cold and barren planet, as opposed to what films show it, such as John Carter of Mars, as a desert world with an arid climate."

"Personally, I liked the section on Venus where it talked about the probes landing on the surface (though not for very long). I actually didn't know (or didn't remember) that we landed on Venus."

"The active colorful weather on Jupiter and hazy weather on Saturn is caused by the heat and sunlight, which is supercool."

"That you would fall through the atmosphere of Jupiter there wouldnt be a sudden boundary between liquid and gas."

"I found the circumstances that created today's Mars and Venus very interesting. It shows just lucky Earth is to have just the right amount of everything."

"That Venus was completely covered in lava."

"How the other terrestrial planets had broken or incomplete cycles, while Earth's cycle was complete."

"Neptune, Jupiter, Uranus, and Saturn are called the jovian planets, and how each don't have a surface of any kind. Thought that all planets had a surface."

"Learning about pluto, because when I was younger Pluto was banned and I had no idea why so it was cool."

"How we distinguish what is a planet and what is not. I never understood why Pluto was all of a sudden not a planet, and was actually kind of bummed out about it. But after doing the reading it makes more sense now."

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

"Jupiter's cloud belts and zones."

"Still trying to figure out why Pluto isn't considered a planet now after all these years."

"If Pluto orbits the sun, and it's classified as a dwarf planet, what's the difference? I would think that if it orbits our sun, it has moons, and it was once calssified as a planet, why go to the trouble of re-classifiying it? Did something about it's composition change, or is it just the discovery of other objects similar in size that exist in the Kuiper belt?"

Identify the relative amounts of these characteristics for Venus, compared to Earth. (Only correct responses shown.)

Interior core heat, today: about the same as Earth [37%]
Geologic activity, today: less than Earth [34%]
Volcanic outgassing, up until now: about the same as Earth [31%]
Heat from the sun: more than Earth [83%]
Amount of atmosphere, today: more than Earth [71%]

Identify the relative amounts of these characteristics for Mars, compared to Earth. (Only correct responses shown.)

Interior core heat, today: less than Earth [74%]
Geologic activity, today: less than Earth [71%]
Volcanic outgassing, up until now: less than Earth [66%]
Heat from the sun: less than Earth [83%]
Amount of atmosphere, today: less than Earth [83%]

Which jovian planet has the coolest interior temperatures?

Jupiter (most massive).	****** [6]
Saturn (most prominent rings).	[0]
Uranus (least active weather patterns).	************* [12]
Neptune (farthest from the sun).	************* [13]
(Unsure/guessing/lost/help!)	**** [4]

I believe Pluto should be a planet.

Strongly disagree.	** [2]
Disagree.	**** [4]
Neutral.	************ [12]
Agree.	************ [12]
Strongly Agree.	***** [5]

Briefly explain your answer to the previous question (whether Pluto should be a planet).

"Well at least they gave it 'planet' in the dwarf planet title."

"A dwarf planet is still a planet to me."

"Well, I don't really care. (Probably not a smart thing to say in a review for an astronomy class.) I don't think that I would take any sort of issue with Pluto being a plant or not. I don't think that it is that important."

"I think it should be a planet mainly because I grew up thinking it was for a long time, however I'm interested on why after so many years they finally considered to not be a planet. I'm mainly curious on the 'qualifications' a planet should have to be considered a plant."

"I don't really care all that much."

"We're hurting Pluto's feelings. Come on, people."

"Taking Pluto off the list of planets is unfair. The new definition of planet relies on information (mass, shape) thhat wasn't known in earlier times."

"Pluto has the qualities of a dwarf planet, but should be still considered a planet because how would you feel if you got kicked out of the solar system because you weren't 'big enough?'"

"Pluto should be a planet because once you say something is a planet there are no take-backs."

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

"Why isn't there an 'average amount' option under the 'How much time did you take for reading?' question?" (Isn't that what the "not too much or too little" choice is for?)

"How many dwarf planets are there that could be considered a planet in our solar system?" (There are five definite dwarf planets so far, and maybe 20 more that could be classified as dwarf planets once we know more information about them.)

"If you had the opportunity to be one of the first people to colonize a planet would you?" (Meh. I'm not sure Mrs. P-dog would be up for that.)

"Do you think Pluto should or shouldn't be a planet, and why?" (Did we not discuss this on the first day of class? I do have strong opinions on this topic.)

Online reading assignment: optical instruments, interference

Physics 205B, spring semester 2015
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 optical instruments and interference.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"I'm starting to get familiar with the lens equation. I understand that some of the problems are conceptual and just knowing the formula won't do you any good if you can't apply it."

"A microscope consists of a short tube that holds two lens apart from each other. A telescope consists of a long tube that holds two lens apart from each other. One lens is an objective lens that takes the light from the object and creates a real image."

"There are similarities between microscopes and telescopes, both being two-lens systems, the objective lens making an image and that image becoming the object for the eyepiece that you can see. However, the microscope's object is very close to the lens, whereas for the telescope it could be extremely far away (different tracings). As a result, the angular magnification is also different for both systems."

"For microscopes, barrel length is from focal length to focal length. For telescopes it is from objective lens to eyepiece lens. In phase speakers will move in and out at the same time but out of phase speakers will do the opposite and one will move in while the other moves out."

"I understood how sound waves traveling different lengths could be both destructive and constructive intereference. If the troughs line up with troughs it is constructive. If the troughs line up with the other sound wave's crest then it is destructive."

"I understand that the sound waves from a stereo system make sense intuitively. If they are out of sync, their troughs and peaks will not line up and they will in essence cancel each other out."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"Applying the constructive and destructive interference conditions of two waves to a problem."

"I was confused with the equations for the telescope and microscope. I was not entirely sure what each variable meant."

"The ray tracings for the microscopes and telescopes confused me."

Identify the type for each of these lenses. (Only correct responses shown.)

Microscope objective: converging [88%]
Microscope eyepiece: converging [68%]
Telescope objective: converging [68%]
Telescope eyepiece: converging [61%]

Identify the ray tracing for each of these lenses. (Only correct responses shown.)

Microscope objective: ray tracing 2 [58%]
Microscope eyepiece: ray tracing 3 or 4 [54%]
Telescope objective: ray tracing 1 [22%]
Telescope eyepiece: ray tracing 3 or 4 [46%]

A (compound) microscope should have a __________ focal length objective lens and a ___________ focal length eyepiece lens in order to maximize its angular magnification.

short; short.	*********************** [23]
short; long.	******** [8]
long; short.	***** [5]
long; long.	* [1]
(Unsure/lost/guessing/help!)	**** [4]

A telescope should have a __________ focal length objective lens and a ___________ focal length eyepiece lens in order to maximize its angular magnification.

short; short.	[0]
short; long.	****** [6]
long; short.	***************************** [29]
long; long.	** [2]
(Unsure/lost/guessing/help!)	**** [4]

Identify the tube/barrel length L definitions for these optical instruments. (Only correct responses shown.)

Microscope: distance from inside focal point to inside focal point [56%]
Telescope: distance from lens to lens [63%]

Classify the various interfering wave examples. (Only correct responses shown.)

1: in phase sources; whole wavelength path difference; constructive [79%]
2: in phase sources; half wavelength path difference; destructive [38%]
3: in phase sources; whole wavelength path difference; constructive [49%]
4: out of phase sources; whole wavelength path difference; destructive [51%]
5: out of phase sources; half wavelength path difference; constructive [54%]
6: out of phase sources; whole wavelength path difference; destructive [59%]

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

"I can't believe we are already starting the sixth week of the semester. Where does all the time go? Pretty soon I won't be in physics anymore:-)." (Yeah, I'm beginning to miss you guys already, too.)

"I need an intervention. I need it."

"I just noticed each group quiz is worth less points, and the maximum for this semester is also less, compared to last semester. What's up with that?" (I am altering the deal. Pray I don't alter it any further. ‪#‎fearleadstoanger‬ #‎angerleadstohate‬ #‎hateleadstosuffering.‬)

"Does it matter if the speakers are connected out of phase? If they move in opposing motions will there still be no sound?" (Yes, ideally the two sounds from each speaker will cancel each other out, if there is no difference in path. This is the principle behind noise-cancelling earphones, where an external microphone detects ambient noise, and drives a speaker with the opposite phase to cancel out the ambient noise as it travels into your ear, leaving all others sounds intact.)

Physics quiz question: angular magnification of a microscope

Physics 205B Quiz 2, spring semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e Problem 24.37

A microscope has an objective lens and an eyepiece with focal lengths of +1.10 cm and +1.20 cm, respectively. The "barrel length" (distance between the lenses) of the microscope is 14 cm. The angular magnification of this microscope is:
(A) –240×.
(B) –19×.
(C) –11×.
(D) –8.3×.

Correct answer (highlight to unhide): (A)

The angular magnification M of a microscope is given by:

M = –(L – f_e)·N/(f_o·f_e),

where L is the distance between the objective and eyepiece, N = 25 cm is the nominal value for the near point, and f_o and f_e are the focal points of the objective and eyepiece, respectively. Thus with the given values given in the statement of the problem, the angular magnification can be calculated directly:

M = –((14 cm – (+1.20 cm))·(25 cm))/((+1.10 cm)·(+1.20 cm)) = –242.42424242...,

or to two significant figures, the angular magnification of this microscope is –240×, where the negative sign denotes an upside-down image viewed through the microscope.

(Response (B) is –N/(f_o·f_e); response (C) is –L/(f_o·f_e); response (D) is –(N – L)/(f_o·f_e).)

Section 30882
Exam code: quiz02wR4y
(A) : 6 students
(B) : 1 student
(C) : 1 student
(D) : 0 students

Success level: 75%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.67

Astronomy current events question: young "yellowball" stars

Astronomy 210L, spring semester 2015
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!)

Whitney Clavin, "Citizen Scientists Lead Astronomers to Mystery Objects in Space," (January 27, 2015)
http://www.jpl.nasa.gov/news/news.php?feature=4462

Internet volunteers discovered "yellowballs" in NASA's Spitzer Space Telescope data, which may be __________ massive stars.
(A) slowly dying.
(B) gas giants orbiting.
(C) black holes swallowing.
(D) early formation stages of.
(E) rapidly approaching.

Correct answer: (D)

Student responses
Sections 30678, 30679, 30680
(A) : 2 students
(B) : 4 students
(C) : 1 student
(D) : 42 students
(E) : 2 students

Astronomy current events question: potentially habitable planets start as "mini-Neptunes?"

Astronomy 210L, spring semester 2015
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!)

Peter Kelley, "Some Potentially Habitable Planets Began as Gaseous, Neptune-like Worlds," (January 28, 2015)
http://www.washington.edu/news/2015/01/28/some-potentially-habitable-planets-began-as-gaseous-neptune-like-worlds/

Researchers propose that potentially habitable planets may begin as gaseous, Neptune-like worlds based on:
(A) computer simulations.
(B) planets passing in front of their stars.
(C) gravity wave measurements.
(D) observations of transferred gases.
(E) disappearing gas giants.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 9 students
(B) : 6 students
(C) : 11 students
(D) : 18 students
(E) : 7 students

Astronomy current events question: gigantic ring system around star J1407

Astronomy 210L, spring semester 2015
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!)

Leonor Sierra, "Gigantic Ring System around J1407b Much Larger, Heavier than Saturn’s," (January 26, 2015)
http://www.rochester.edu/newscenter/gigantic-ring-system-around-j1407b/

The gigantic ring system surrounding sun-like star J1407 was discovered by analyzing changes in brightness as the rings __________ the star.
(A) are vaporized by.
(B) slowly fall in towards.
(C) form exomoons around.
(D) pass in front of.
(E) are flung outwards from.

Correct answer: (D)

Student responses
Sections 30678, 30679, 30680
(A) : 4 students
(B) : 4 students
(C) : 14 students
(D) : 26 students
(E) : 3 students

Online reading assignment: corrective optics, magnifiers

Physics 205B, spring semester 2015
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 corrective optics and magnifiers.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.

"A two-lens system is what corrects visual defects for people; contacts or glasses coupled with the eyes. Ultimately, it's two lens equations that make a second image (q₁) that acts as a second object (p₂) so the eye can focus on the object (p₁), but treat it as a second real upright image (q₂). Knowing the near point or far point distances, contacts or glasses can be prescribed that correct these distances using the thin-lens equation."

"More about diverging and converging lenses--I had a lot of trouble with it because I didn't understand which images they produced."

"How optical instruments actually use a minimum of two lenses. Also, I learned a lot about how spectacular eyes are and how they function similar to a camera."

"The 1/p + 1/q = 1/f relationship is used to understand how cameras and eyes focus real images differently. A camera will have a set focal length, since the lens cannot change shape, so the image distance must change in order to focus on different object distances. Alternatively, the eye will adjust the lens thickness and focal length in response to the changing location of the object, keeping the image distance the same."

"Myopia requires a diverging lens to bring the images closer. While hyperopia uses a converging lens to push images away."

"I understand a bit more of the science behind knowing why a person would need bifocals. And I learned that in a two lens system we take it one lens at a time. I actually found this stuff really interesting as I wear glasses."

"Angular size is a measure of how large an angle it subtends with your eye at the origin, and is a measure of how big something "seems" from your viewpoint. Angular modification 'M' is a numerical factor denoting how much larger the angular size of something appears as seen through a magnifier, compared to the naked eye. If a converging lens with focal length f is used a magnifier, the angular magnification is the ratio of the angular size as seen through the magnifier, compared to the angular size as seen through an unaided eye.This is the ratio of the near point (25cm) to the focal length f."

"Essentially a lens produces a 'corrected' virtual image to compensate for the eye's deficiency, which the eyes pick up and interpret correctly. Essentially, by figuring out the type of deficiency, and plugging in the right values we can pretend to be optometrists and figure out the focal point correction, which then we can use to find the refractive power 1/f."

"We are dealing with two lenses now."

"Diving deeper into properties of lenses."

"The eye."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.

"I'm mainly getting myself mixed-up with all the new variables."

"I'm lost on how to use the two-step model with the myopia and hyperopia prescription."

"I find interpreting ray tracing diagrams to distinguish between real and virtual images a really hard process."

"I had a hard time understanding the two lens system equations and how to use it in prescription cases. I also still have issues with the ray tracings."

"Overall, I understand the thin lens equation, however, I'm having difficulty applying the equation when given different values. This is where I need the greatest clarification."

"Lost me a little bit on the magnifiers."

In general, a converging lens will produce virtual, upright images located __________ the original object.

closer than.	******* [7]
at the same distance as.	*** [3]
farther than.	************************* [25]
(Unsure/lost/guessing/help!)	* [1]

In general, a diverging lens will produce virtual, upright images located __________ the original object.

closer than.	*************************** [27]
at the same distance as.	[0]
farther than.	******** [8]
(Unsure/lost/guessing/help!)	* [1]

Identify the type of lens used for these optics. (Only correct responses shown.)

Glasses/contacts to correct for myopia: diverging [80%]
Glasses/contacts to correct for hyperopia: converging [83%]
Glasses/contacts to correct for presbyopia: converging [31%]
Magnifying lenses: converging [51%]

State the units of optical power for lenses, and briefly describe the relationship between optical power P and focal length f.

"Diopters. The optical power P is equal to the reciprocal of the focal length f."

"The unit of optical power for lenses is m^-1. The optical power is equal to 1/f."

"I am not sure."

"€8-0 Freak out!"

Explain the difference between the two types of magnification, m and M.

"Little m is linear magnification while big M is angular magnification."

"M stands for 'angular magnification' which is a numerical factor denoting how much larger the angular size of something appears as seen through a magnifier compared to with just the naked eye. The magnitude of the transverse magnification (m) is the ratio of the image size to the object size; the sign of m is determined by the orientation of the image."

"The angular magnification M (upper-case M, to distinguish it from linear magnification lower-case m) is a numerical factor denoting how much larger the angular size of something appears as seen through a magnifier, compared to with just the unaided eye. Little m is just image height divided by object height."

"m- is micro, M- is mega."

"I'm honestly lost as to what the difference is."

If an object is brought closer to your eye, its angular size will:

increase.	********************************* [33]
decrease.	**** [4]
remain unchanged.	* [1]
(Unsure/lost/guessing/help!)	** [2]

When a converging lens is used as a simple magnifier, the object is placed at a distance p = __________ in front of (to the left of) the lens.

+∞.	*** [3]
+25 cm (at your near point).	***************** [17]
+f (at the focal point of the lens).	********** [15]
(Unsure/lost/guessing/help!)	***** [5]

The ray tracing that best matches when a converging lens is used as a simple magnifier is:

#1.	******* [7]
#2.	** [2]
#3.	*** [3]
#4.	****** [6]
#5.	********** [10]
(Unsure/lost/guessing/help!)	******** [8]

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

"I kinda forgot some of the stuff we learned in this chapter because of the nearly two weeks we had between classes and me not reviewing the material like most of the students in our class =]"

"I don't understand how someone could use bifocals, I think that would drive me crazy, but I guess you adapt." (No, as a bifocal wearer, you never really do. The bottoms of my eyes always seem like they're welling up with tears. #thesearenttearsimjustleakingfeelings)

"Look at this comment, just look at it." (What, through my bifocals? Oh wait, so that's what they're for.)

"I'm gonna study more."

"No comment." (You just did.)

Online reading assignment: atmosphere problems, Earth, the moon, Mercury (SLO campus)

Astronomy 210, spring semester 2015
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 problems caused by the atmosphere for telescope observing, Earth, and the impacted worlds: the moon, and Mercury.


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.

"That the moon can be thought of as a piece of Earth's debris because it is hypothesized that an object smashed into protoearth, causing a piece of it to break off."

"Dark skies--I hate light pollution because I love being able to see stars."

"How turbulence can actually affect the telescope images of space. Isn't air supposed to be invisible? Guess not!"

"Craters on different types of asteroids and planets interesting--I didn't know there was an order to when features appeared."

"First, that the mountains are a relatively new developments on Earth. Secondly that the green house effect is not entirely a bad thing, since with out it the planet would be freezing."

"The cycle of carbon dioxide through the Earth's atmosphere. I thought that carbon dioxide entered the atmosphere through plants."

"I thought the concept of light pollution was distressing. It's sad to think that modern civilization has kept humans from seeing the natural beauty in the world."

"Visualizing the different wavelength sizes and how they are constantly around us is a trippy thought. It's interesting to me because I wonder with all the electronics we have nowadays if this cocktail of different waveengths affects us mentally somehow but we are unaware of it. I also forgot that sound waves can't travel through space. Cool!"

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

"I still don't understand how we can measure a planet's core without going into there."

"Would you explain the history of the moon/Mercury in simpler terms? I found the text to be wordy and kind of confusing."

"How we know so much about Mercury and those other further planets when we have never been to them. Also, I realize that we have advanced technology but I am confused how we can not only have a devise find the planets, but also how they are so clear and visible. And how do we know how large the moon and Mercury’s core is?"

"Adaptive optics--I don't understand how the computer can warp the image to make it the actual shape after turbulance from the atmosphere. "

Stars to appear to "twinkle" in the night sky because of:

"Because you are looking through the earth's atmosphere to see the star, turbulence from the air in this atmosphere will blur and distort the stars' image making it appear to twinkle."

"Because its traveling through time and air, so we are seeing it as it comes through those."

"Stars are twinkling in the sky because there is so much air between the star were seeing and where we are that the stars seem to twinkle."

A large modern optical telescope in outer space would have images with better __________ than a comparable ground-based telescope.

brightness.	*** [3]
resolution.	*************** [15]
magnification.	[0]
(None of the above choices.)	** [2]
(Two of the above choices.)	************ [12]
(All of the above choices.)	************ [12]
(Unsure/guessing/lost/help!)	*** [3]

Identify how carbon dioxide enters and how it is taken out of Earth's atmosphere.
(Only correct responses shown.)

Enters atmosphere from: volcanoes [45%]
Taken out of atmosphere by: oceans [43%]

Identify the oldest (longest ago) to the youngest (most recent) features on the moon.
(Only correct responses shown.)

Craters partially filled in with flat lava plains: oldest (formed longest ago) [34%]
Flat lava plains: middle [21%]
Craters on top of flat lava plains: youngest (formed most recently) [43%]

Identify the oldest (longest ago) to the youngest (most recent) features on Mercury.
(Only correct responses shown.)

Large crater basins: oldest (formed longest ago) [60%]
Lava-filled lowlands: middle [36%]
Long curving ridges: youngest (formed most recently) [45%]

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

"Was curious what the greenish color is at the end of the International Space Station video." (That's the aurora borealis, when charged particles streaming from the sun slam into Earth's upper atmosphere, making it glow certain colors. Same principle as using electricity to zap atoms in a neon sign to make them glow a certain color.)

"There was a lot of information in these sections and I don't know what the important things to know are." (Primarily the material in the flashcard question packets, and the in-class activities. The presentation slides are meant to fill in details that the textbook doesn't cover.)

"I love you." (No, you just love astronomy. You do love astronomy, right? RIGHT? #wut)

"I went to Big Sur for the first time this weekend and slept under that stars! No light pollution there! The night sky was incredible and I was probably a little obnoxious with my star facts but being able to see everything so clear got me excited!" (Whoa there, calm down. That's just the astronomy love, talking.)

"The best thing said in the presentation preview: 'We are all caretakers for our planet, so let's make sure to read the owner's manual.'" (And in the owner's manual, it says, "If you break it, you own it.")

"If Earth's oceans are absorbing carbon pollution does that mean if we stopped producing man-made greenhouse gases, in time the world would restore itself?" (Theoretically, yes, but we'll just have to find out for ourselves what will eventually happen, depending on what we do. Let's all read that owner's manual again.)

Astronomy quiz question: Edmund Scientific Astroscan® resolving power

Astronomy 210 Quiz 3, fall semester 2012
Cuesta College, San Luis Obispo, CA

The resolving power for the Edmund Scientific Astroscan® Newtonian focus reflector shown at right depends on:
(A) the width of the tube.
(B) the length of the tube.
(C) twice the length of the tube.
(D) three times the length of the tube.

Correct answer (highlight to unhide): (A)

The resolving power of a telescope depends on the diameter of the primary mirror (or lens).

Section 70158
Exam code: quiz03s3Er
(A) : 15 students
(B) : 14 students
(C) : 6 students
(D) : 2 students

Success level: 44% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.70

Astronomy quiz question: Celestron NexStar® primary focal length

Astronomy 210 Quiz 3, fall semester 2012
Cuesta College, San Luis Obispo, CA

The primary focal length for the Celestron NexStar® Maksutov-Cassegrain focus reflector shown at right is approximately:
(A) the width of the tube.
(B) the length of the tube.
(C) twice the length of the tube.
(D) three times the length of the tube.

Correct answer (highlight to unhide): (C)

Light enters the tube and is then reflected off of the primary mirror at the back, coming to a focus as it travels back up the tube, then deflected by the secondary mirror at the front of the tube, then going back down the tube to come to a focus (after reflecting off of another secondary mirror); thus traveling twice along the length of the tube while coming to a focus.

Section 70160
Exam code: quiz03ni3R
(A) : 1 student
(B) : 2 students
(C) : 23 students
(D) : 3 students

Success level: 81% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.22

Online reading assignment: atmosphere problems, Earth, the moon, Mercury (NC campus)

Astronomy 210, spring semester 2015
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 problems caused by the atmosphere for telescope observing, Earth, and the impacted worlds: the moon, and Mercury.

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.

"How the ocean soaks up the carbon dioxide emitted from volcanic eruptions and other natural sources. It helped how you used the analogy with the soda cans in the slides."

"The theory of how the moon was formed; I never thought of it as something that had 'run' into Earth."

"Earth's active crust and how it is constantly changing. It just blows me away to think of how amazing the planet we live in is! Just wish we, as a society, could care a little more."

"That NASA is using airplanes to gather images of space, especially because that program is based in San Jose, so close to home."

"The comparison to being underwater and Earth's atmosphere being essentially an ocean of air. I never thought of it that way but it makes sense."

"Now carbon dioxide enters and leaves Earth's atmosphere."

"All of it because I had taken an astronomy class back in the day, and I feel like I had never learned much about these topics."

"That planets have different kinds of atmospheres. It's weird to think that some plants don't even have atmospheres because of the way that they were created differently."

"I really liked learning about light pollution. I've personally noticed that the sky is so much more vivid in areas away from big cites. Even within our property the stars are much brighter than in downtown San Luis Obispo."

"The turkey/cornish game hen analogy is a great way to explain the difference in the sizes of the cores of Mercury, Earth and the moon. I'm not sure I would've understood if you had tried to explain it any other way."

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

"Atmospheric opacity and the electromagnetic spectrum is confusing for me to read. If we could go over how to read it exactly I would appreciate that."

"Everything confuses me."

"Tectonic plates, just because they're something I'm not super familiar with."

"I'm lost/guessing/need help!"

"I don't understand the chronology of features on the moon and Mercury (craters, mare, etc.)."

"Just need a little clarification on the the features of the moon."

"Adaptive optics--it's difficult for me to grasp things without a more physical understanding of what I'm trying to grasp."

"I am very lost on the telescope measurements from last class."

Stars to appear to "twinkle" in the night sky because of:

"Our view is obstructed by particles, air, and wind making the stars appear to twinkle."

"Atmospheric turbulence, which means when we look up into the sky we get a distorted view of the stars due to rippling in the atmosphere."

A large modern optical telescope in outer space would have images with better __________ than a comparable ground-based telescope.

brightness.	** [2]
resolution.	************* [13]
magnification.	[11]
(None of the above choices.)	[0]
(Two of the above choices.)	* [1]
(All of the above choices.)	******* [7]
(Unsure/guessing/lost/help!)	** [2]

Identify how carbon dioxide enters and how it is taken out of Earth's atmosphere.
(Only correct responses shown.)

Enters atmosphere from: volcanoes [62%]
Taken out of atmosphere by: oceans [62%]

Identify the oldest (longest ago) to the youngest (most recent) features on the moon.
(Only correct responses shown.)

Craters partially filled in with flat lava plains: oldest (formed longest ago) [38%]
Flat lava plains: middle [27%]
Craters on top of flat lava plains: youngest (formed most recently) [62%]

Identify the oldest (longest ago) to the youngest (most recent) features on Mercury.
(Only correct responses shown.)

Large crater basins: oldest (formed longest ago) [42%]
Lava-filled lowlands: middle [27%]
Long curving ridges: youngest (formed most recently) [38%]

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

"Am I confused? Just wondering if I read this right: the moon was formed out of an collision that happened on Earth?" (Yes, that's what evidence currently suggests really happened!)

"I am liking the class style so far; the in-class activities usually help clear up the questions/problems I have in the homework."

"Can you teach us this stuff rather than having us read about it on our own?" (Well, depends if you were able to read it and get it on your own... But looking at a lot of the class' responses, we'll have to go through some of this extensively in class.)

"Will there be other observation nights at the North County telescope shelter? (Yes, tentatively on April 2, weather permitting.)

"The formation of stars gives off infrared energy, while the death of stars gives off x-rays and gamma rays. Why is this? (Stars form slowly as gravity gathers in gas and dust, and this heats it up to several thousands of degrees, releasing medium-energy photons such as infrared (think of charcoal briquette hotnesses). However, as we'll see later this semester, stars die catastrophically, releasing energy that heats it up to several millions of degrees, releasing higher energy photons such as x-rays and gamma rays (think of thermonuclear explosion hotnesses).)

"So...sound is not part of the electromagnetic spectrum because vibrations of the atoms in the atmosphere is what produces sound?" (Yes, that's why sound is different than light, which is vibrations of electromagnetic fields produced by charges like individual atoms, free electrons, electrons inside atoms, and electrons traveling up and down a metal antenna.)

"Star Wars or Star Trek? Do not take this question lightly." (*Does Jedi hand-wave* This is not the answer you're looking for. But then again, there's an "epic trailer" that might answer your question.)

Physics quiz question: frequency of Blu-ray™ laser light in polycarbonate

Physics 205B Quiz 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Comprehensive Problem 22.67(a)

A Blu-ray Disc™ player uses laser light (wavelength[*] 405 nm) in air (index of refraction of 1.000) that goes through a layer of polycarbonate (index of refraction[**] of 1.585). The frequency of this light in polycarbonate is:
(A) 4.67×10¹⁴ Hz.
(B) 7.41×10¹⁴ Hz.
(C) 1.17×10¹⁵ Hz.
(D) 1.22×10²⁰ Hz.

[*] en.wikipedia.org/wiki/File:Comparison_CD_DVD_HDDVD_BD.svg.
[**] physics.info/refraction/.

Correct answer (highlight to unhide): (B)

The relations between the index of refraction and the speed of light, for air (medium 1) and for polycarbonate (medium 2), are:

n₁ = c/v₁,

n₂ = c/v₂,

where the given (or assumed to be known) quantities, unknown quantities, and quantities to be explicitly solved for are denoted. Also the relations between wavelength, speed, and frequency are:

λ₁ = v₁/f₁,

λ₂ = v₂/f₂.

However, the frequency of the light in air is the same as the frequency it has in polycarbonate, such that:

f₂ = f₁,

f₂ = v₁/λ₁,

f₂ = (c/n₁)/λ₁,

f₂ = c/(n₁·λ₁) = (3.00×10⁸ m/s)/((1.000)·(405×10^–9 m)),

f₂ = 7.40740740741×10¹⁴ s^–1,

or to three significant figures, 7.41×10¹⁴ Hz.

(Response (A) is c/(λ₁·n₂); response (C) is (c·n₂)/λ₁; response (D) is c·(405×10⁹ m).)

Sections 30882, 30883
Exam code: quiz01c0Co
(A) : 24 students
(B) : 21 students
(C) : 3 students
(D) : 0 students

Success level: 44%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.41

Physics quiz question: diagonally polarized light, different polarizer sets

Physics 205B Quiz 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

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

Light polarized at a 45° angle (as seen traveling towards you) passes through a set of two ideal polarizing sheets. If the amount of light transmitted after passing through both polarizers is 25% of the original polarized light, the first polarizer transmission axis is ________, and the second polarizer transmission axis is __________.
(A) horizontal; parallel to the original light polarization.
(B) parallel to the original light polarization; horizontal.
(C) (Both of the above choices.)
(D) (None of the above choices.)

Correct answer (highlight to unhide): (A)

From Malus' law, the fraction of polarized light passing through a polarizer is given by cos²θ, where θ is the angle between the original polarization and the transmission axis of the polarizer. If θ = 0°, then the polarized light is parallel to the transmission axis of the polarizer, then all of the light will pass through the polarizer.

For the "horizontal; parallel" set of polarizers, the fraction of light passing through the first polarizer is cos²(45°) = 0.5, and will have a horizontal polarization. The fraction of this light passing through the second polarizer is cos²(45°) = 0.50, and will have a polarization that is at a clockwise angle of 45° with respect to the vertical. Thus the fraction of the original polarized light that passes through both polarizers is the product 0.50·cos²(45°) = 0.25.

For the "parallel; horizontal" set of polarizers, the fraction of light passing through the first polarizer is 1, and will still have its diagonal polarization. The fraction of this diagonally polarized light passing through the second horizontal polarizer is cos²(45°) = 0.50, and will have a horizontal polarization.

Thus only the first set of polarizers will pass "25% of the original polarized light."

Student responses
Sections 30882, 30883
Exam code: quiz01c0Co
(A) : 19 students
(B) : 6 students
(C) : 18 students
(D) : 5 students

Success level: 40%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.51

Physics quiz question: reflection, refraction at cocoa butter-Pyrex® interface

Physics 205B Quiz 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

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

"Cocoa Butter"
John (star5112)
flic.kr/p/Agns9

Light of wavelength 585 nm in melted cocoa butter (index of refraction[*] of 1.457) is incident at an angle of 60.0° at the interface between melted cocoa butter and Pyrex® (index of refraction[*] 1.474). (Drawing is not to scale.) As measured from the normal, the reflected angle in melted cocoa butter is __________ the transmitted angle in Pyrex®.
(A) less than.
(B) equal to.
(C) greater than.
(D) (There is no actual transmitted ray in Pyrex®.)
(E) (Not enough information is given.)

[*] physics.info/refraction/.

Correct answer (highlight to unhide): (C)

Snell's law relates the indices of refraction with the incident and transmitted angles, where cocoa butter is medium 1, and Pyrex® is medium 2:

n₁·sinθ₁ = n₂·sinθ₂,

and the law of reflection relates the incident and (specularly) reflected angles in cocoa butter:

θ_incident = θ_reflected,

where the given (or assumed to be known) quantities, unknown quantities, and quantities to be explicitly solved for (or compared) are denoted.

From the law of reflection, the reflected angle in cocoa butter must also be 60.0°:

θ_incident = θ_reflected,

60.0° = θ_reflected.

From Snell's law, since the index of refraction for cocoa butter n₁ is greater than the index of refraction n₂ for Pyrex®, then the incident angle θ₁ in cocoa butter must be smaller than the transmitted angle θ₂ in Pyrex®. The transmitted angle θ₂ in Pyrex® can also be solved for directly:

n₁·sinθ₁ = n₂·sinθ₂,

(n₁/n₂)·sinθ₁ = sinθ₂,

sin^–1((n₁/n₂)·sinθ₁) = θ₂,

sin^–1((1.457/1.474)·sin(60.0°)) = θ₂,

sin^–1(0.85603732247) = θ₂,

58.8745233263° = θ₂,

and because the reflected angle in cocoa butter is 60.0°, and the transmitted angle in Pyrex® (to three significant figures) is 58.9°, then the reflected angle in cocoa butter is greater than the transmitted angle in Pyrex®.

Student responses
Sections 30882, 30883
Exam code: quiz01c0Co
(A) : 9 students
(B) : 11 students
(C) : 27 students
(D) : 1 student

Success level: 56%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.32

Physics quiz question: crown glass versus flint glass

Physics 205B Quiz 1, spring semester 2015
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Question 23.7


Light in crown glass and light in flint glass are each transmitted out into air. (Drawing is not to scale.) __________ has a greater index of refraction.
(A) Crown glass.
(B) Flint glass.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (B)

Snell's law relates the indices of refraction with the incident and transmitted angles:

n_{crown glass}·sin(θ_{crown glass}) = n_air·sin(θ_air),

n_{flint glass}·sin(θ_{flint glass}) = n_air·sin(θ_air),

where the given (or assumed to be known) quantities, unknown quantities, and quantities to be explicitly solved for (or compared) are denoted.

Since the terms n_air·sin(θ_air) appear in both Snell's law equations, we can then eliminate those two terms and set the following quantities equal to each other, in order to directly compare the indices of refraction for crown glass and flint glass:

n_air·sin(θ_air) = n_air·sin(θ_air),

n_{crown glass}·sin(θ_{crown glass}) = n_{flint glass}·sin(θ_{flint glass}),

n_{crown glass}·sin(41.3°) = n_{flint glass}·sin(39.6°),

and because sin(41.3°) is greater than sin(39.6°), then n_{crown glass} must be less than n_{flint glass}, such that flint glass has the higher index of refraction. More specifically:

(sin(41.3°)/sin(39.6°))·n_{crown glass} = n_{flint glass},

(0.6600016679/0.6374239897)·n_{crown glass} = n_{flint glass},

1.035420189·n_{crown glass} = n_{flint glass},

where to three significant figures, the index of refraction of flint glass is 1.04× that of crown glass (or 4% greater than that of crown glass).

Student responses
Sections 30882, 30883
Exam code: quiz01c0Co
(A) : 12 students
(B) : 35 students
(C) : 1 student
(D) : 0 students

Success level: 73%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.48