20180217

Physics quiz question: polarized light transmitted through two polarizers

Physics 205B Quiz 1, spring semester 2018
Cuesta College, San Luis Obispo, CA

Polarized light passes through two polarizers with polarization axes turned as shown below.


The total fraction of the incident light intensity transmitted through both polarizers is:
(A) 0.
(B) 0.19.
(C) 0.38.
(D) 0.56.

Correct answer (highlight to unhide): (B)

The fraction of the diagonally polarized light that passes through the vertical polarizer 1 is cos2θ, where the angle θ = 60° is measured between the diagonal polarization of the light entering polarizer 1 (60° clockwise from vertical) and the transmission axis of polarizer 1 (vertical). The light after passing through polarizer 1, but before passing through polarizer 2 is now vertically polarized, having a polarization that matches the transmission axis of polarizer 1.


The fraction of this vertically polarized light that passes through polarizer 2 is again cos2θ, but where the angle θ = 30° is measured between the polarization of the light entering polarizer 2 (vertical) and the transmission axis of polarizer 2 (30° counterclockwise from the vertical).


Thus the fraction of light that passes through both polarizer 1 and polarizer 2 is:

cos2(60°)·cos2(30°) = (1/4)⋅(3/4) = (3/16) = 0.1875,

or to two significant figures, 0.19 of the original unpolarized intensity.

(Response (C) is (1/2)·cos2(30°), which would be the fraction of unpolarized light that would pass through both polarizers; and response (D) is cos2(30°)⋅cos2(30°).)

Student responses
Sections 30882, 30883
Exam code: quiz01AM0l
(A) : 4 students
(B) : 25 students
(C) : 5 students
(D) : 1 student

Success level: 71%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.45

Physics quiz question: water wavelength in spharelite

Physics 205B Quiz 1, spring semester 2018
Cuesta College, San Luis Obispo, CA

Light of wavelength 476 nm in water (index of refraction of[*] 1.33) with an incident angle of 16.0° 
is transmitted into sphalerite (index of refraction of 2.43). (Drawing is not to scale.) The wavelength of this light traveling through sphalerite is:
(A) 196 nm.
(B) 261 nm.
(C) 358 nm.
(D) 870 nm.

[*] physics.info/refraction/.

Correct answer (highlight to unhide): (B)

The relations between the index of refraction and the speed of light, for water (medium 1) and for spharelite (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 spharelite is the same as the frequency it has in water, such that:

f1 = f2,

(v1/λ1) = (v2/λ2),

λ2 = λ1·(v2/v1),

λ2 = λ1·((c/n2)/(c/n1)),

λ2 = λ1·(n1/n2) = (476 nm)·(1.33/2.43) = 261 nm.

(Response (A) is (476 nm)/(1.33); response (C) is (218 nm)/(2.43); response (D) is (476 nm)⋅(2.43/1.33).)

Sections 30882, 30883
Exam code: quiz01AM0l
(A) : 4 students
(B) : 28 students
(C) : 1 student
(D) : 2 students

Success level: 80%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.64

Physics quiz question: diamond-air interface total internal reflection?

Physics 205B Quiz 1, spring semester 2018
Cuesta College, San Luis Obispo, CA

Light with an incident angle of 44.8° in diamond strikes the interface between diamond (index of refraction[*] 2.418) and air (index of refraction 1.000). (Drawing is not to scale.) As measured from the normal, the angle of the transmitted ray in air is __________ 44.8°.
(A) less than.
(B) equal to.
(C) greater than.
(D) (There is no transmitted ray in air.)

[*] physics.info/refraction/.

Correct answer (highlight to unhide): (D)

The critical angle for light incident on a diamond-air interface is given by:

θc = sin–1(n2/n2) = sin–1(1.000/2.418) = 24.43°.

Since the incident ray in diamond has an angle greater than the critical angle, it is totally internally reflected back into diamond, and thus there is no transmitted ray in air.)

Student responses
Sections 30882, 30883
Exam code: quiz01AM0l
(A) : 2 students
(B) : 0 students
(C) : 8 students
(D) : 25 students

Success level: 71%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.45

20180215

Astronomy quiz question: phase during partial solar eclipse

Astronomy 210 Quiz 2, spring semester 2018
Cuesta College, San Luis Obispo, CA

A partial solar eclipse will be visible for observers in portions of South America and Antartica on February 15, 2018[*]. During this partial solar eclipse, the moon will be in its __________ phase.
(A) new.
(B) first quarter.
(C) full.
(D) third quarter.
(E) (Depends on the time of day.)

[*] timeanddate.com/eclipse/solar/2018-february-15.

Correct answer (highlight to unhide): (A)

During any type of solar eclipse, the moon is directly between the sun and Earth, and must be in its new phase.

Section 30674
Exam code: quiz02npP4
(A) : 15 students
(B) : 6 students
(C) : 3 students
(D) : 0 students
(E) : 0 students

Success level: 66% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.63

Section 30676
Exam code: quiz02sn4E
(A) : 21 students
(B) : 4 students
(C) : 11 students
(D) : 4 students
(E) : 0 students

Success level: 54% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.91

Astronomy quiz question: planets visible at sunset?

Astronomy 210 Quiz 2, spring semester 2018
Cuesta College, San Luis Obispo, CA

The locations of Saturn, Earth, and Jupiter are shown in the diagram below (not to scale, and orbits have been simplified as circles instead of ellipses).


Which planet(s) will be visible at sunset?
(A) Saturn.
(B) Jupiter.
(C) (Both of the above choices.)
(D) (Neither of the above choices.)

Correct answer (highlight to unhide): (C)

If a line is drawn from Earth to the sun, the observer at sunset (6 PM) is located perpendicular that line. Since Saturn and Jupiter are both above that horizon line, they will both be visible at that time, where Saturn would be low over the east horizon, and Jupiter would be low over the west horizon.)


Section 30676
Exam code: quiz02sn4E
(A) : 17 students
(B) : 4 students
(C) : 13 students
(D) : 6 students

Success level: 35% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.45

Astronomy quiz question: planets visible at midnight?

Astronomy 210 Quiz 2, spring semester 2018
Cuesta College, San Luis Obispo, CA

The locations of Saturn, Earth, and Jupiter are shown in the diagram below (not to scale, and orbits have been simplified as circles instead of ellipses).


Which planet(s) will be visible at midnight?
(A) Saturn.
(B) Jupiter.
(C) (Both of the above choices.)
(D) (Neither of the above choices.)

Correct answer (highlight to unhide): (A)

If a line is drawn from Earth to the sun, the observer at midnight (12 AM) is located along that line, in the middle of the night side of Earth. Since Saturn is above that horizon line, it will be visible at that time, and would be located somewhere high in the sky. (Since Jupiter is below that horizon line, it would not be visible at midnight.)


Section 30674
Exam code: quiz02npP4
(A) : 18 students
(B) : 2 students
(C) : 3 students
(D) : 1 student

Success level: 77% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.09

Astronomy quiz archive: eclipses/history of astronomy

Astronomy 210 Quiz 2, fall semester 2017
Cuesta College, San Luis Obispo, CA

Section 70158, version 1
Exam code: quiz02Sdi3


Section 70158
0- 8.0 :   ** [low = 3.0]
8.5-16.0 :   ********
16.5-24.0 :   ****************** [mean = 22.0 +/- 7.8]
24.5-32.0 :   ***********
32.5-40.0 :   ***** [high = 36.5]


Section 70160, version 1
Exam code: quiz02NoL4


Section 70160
0- 8.0 :   * [low = 6.5]
8.5-16.0 :   ******
16.5-24.0 :   *********** [mean = 23.3 +/- 8.4]
24.5-32.0 :   ******
32.5-40.0 :   ***** [high = 40.0]

20180214

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

Astronomy 210, spring semester 2018
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 we are literally living in the ocean of air. This was interesting because I never thought of all the ripples and things we see underwater in a scientific way."

"Atmospheric turbulence and the explanation of our 'ocean of air.' I had no idea that the atmosphere could cause views through a telescope or the human eye to be distorted. I enjoyed the super neat way you chose to explain it, too."

"That turbulence causes the twinkling that I see in stars. I had never really thought of it that way, and it really served to cement a thought in my head about nature."

"The reason behind why stars twinkle--I just assumed their brightness caused that but it is how its light bounces around once it goes through our atmosphere."

"Light pollution interested me because depending on where you are and how little or how much light pollution is in the sky affects how many stars you can see with the naked human eye."

"The greenhouse effect; more specifically the dangers of too much greenhouse effect. When the suns energy is converted to infrared light and is unable to escape the interior becomes too hot and almost deadly. The child being trapped in the car and in danger of dying from heat exhaustion is the perfect example of too much greenhouse effect."

"What really caught my attention was the continental drift, and the comparison to gravy skins. I am a huge fan of the day after Thanksgiving leftovers and know very well what the gravy looks like when its not hot. This was a very personal and easy visual for me."

"The youngest and oldest features of the moon and Mercury, because it's really cool that some parts of the moon are older than others, especially since it had never occured to me that some parts were older than others."

"I had never heard of the large impact hypothesis which explains how the moon was supposedly formed and that was just interesting because id always wondered where the moon comes from."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I guess that the only thing that would be confusing for me is that of adaptive optics. Is the mirror that is flexible an actual mirror? How does the computer measure what is actual disturbance?"

"Active optics confuses me because I am not sure how it affects the atmosphere turbulence."

"How someone can make an image such that is has the actual shape after turbulance from the atmosphere (twinkling stars)."

"The problem of the opacity of our atmosphere. And mostly the electromagnetic spectrum."

"I didn't really understand the history of Earth's moon and how it formed. I am also confused about how lava plains were made. Please go over that."

"I was having a really hard time understanding the order the things that shape the moon and Mercury. The book was really unclear and I read it multiple times but I am still confused."

"How Mercury actually formed is still confusing."

A large modern optical telescope in outer space would have images with better __________ than a comparable ground-based telescope.
brightness.   *** [3]
resolution.   **************** [16]
magnification.   ** [2]
(None of the above choices.)   [0]
(Two of the above choices.)   **** [4]
(All of the above choices.)   ****** [6]
(Unsure/guessing/lost/help!)   **** [4]

Stars to appear to "twinkle" in the night sky because of...
"Stars twinkle because of turbulence in the atmosphere of the Earth. As the atmosphere churns, the light from the star is refracted in different directions. This causes the star's image to change slightly in brightness and position"

"Stars twinkle from our perspective because we are seeing them through our turbulent atmosphere, which bends the light and creates the apparent flashing look."

"They are moving?"

"Gases reacting with one another and causing flares?"

Identify how carbon dioxide enters and how it is taken out of Earth's atmosphere.
(Only correct responses shown.)
Enters atmosphere from: volcanoes [41%]
Taken out of atmosphere by: oceans [38%]

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) [43%]
Flat lava plains: middle [20%]
Craters on top of flat lava plains: youngest (formed most recently) [31%]

Identify the oldest (longest ago) to the youngest (most recent) features on Mercury.
(Only correct responses shown.)
Large crater basins: oldest (formed longest ago) [57%]
Lava-filled lowlands: middle [40%]
Long curving ridges: youngest (formed most recently) [57%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Is there less atmospheric turbulence in Hawaii, where a lot of the largest telescopes are? Is that why Hawaii is such a good place for telescopes?" (I think the one of the main reasons why is that the jet stream (the main source of upper atmospheric turbulence) does not typically pass right over Hawaii most of the time.)

"Could you please go over the details of the surfaces of the Moon and Mercury?"

"How do they decide what a young/old feature on a planet is?"

"I was a little bit confused by the explanation of the creation of the moon. Is there a definite answer as to how it was created, or just the high probability that it was created as fragment of a planetary collision?" (The large impact hypothesis is actually not only supported by geologic evidence in rocks brought back from the moon; it is the only hypothesis remaining that is supported by that evidence.)

"Will there be study guides posted for the midterms and final?" (Yes, and there will be review sessions as well.)

"Where does P-dog get his fresh haircuts?"

Online reading assignment: interference

Physics 205B, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students have a bi-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 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.
"When two light waves arrive the same point they combine. they can reinforce each other during constructive interference, or cancel each other through destructive interference."

"With constructive interference the waves are in sync and reinforce each other and with destructive interference the waves cancel each other out. There are also different types of source phases and path length differences that can affect whether a wave is constructive or destructive."

"I understand that when sound waves troughs and crests line up (move in unison) there is constructive interference. On the other hand, when the troughs and crests don't line up (out of unison) there is destructive interference."

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 found distinguishing between in phase and out of phase sources slightly confusing. I'm not entirely sure whether a wave is considered to be constructive or destructive when the sources are out of phase. I just need some examples and I think I'll be able to figure it out."

"I don't understand the source phase and path length differences."

"I don't understand how to determine the path length differences."

"I have a good understanding of this material. Maybe some in-class examples of constructive and destructive interference would be helpful."

"I didn't find anything really confusing this lesson."

Classify the various interfering wave examples. (Only correct responses shown.)
1: in phase sources [92%]; whole wavelength path difference [96%]; constructive [92%]
2: in phase sources [63%]; half wavelength path difference [96%]; destructive [92%]
3: in phase sources [83%]; whole wavelength path difference [83%]; constructive [92%]
4: out of phase sources [83%]; whole wavelength path difference [67%]; destructive [88%]
5: out of phase sources [42%]; half wavelength path difference [63%]; constructive [83%]
6: out of phase sources [92%]; whole wavelength path difference [42%]; destructive [88%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Are you enjoying the Olympics?" (Only while watching Mrs. P-dog's cousin compete in slopestyle and big air snowboarding.)

I think I got these diagrams...but sometimes I think I understand something and it later turns out that I'm entirely wrong."

"Lab due next Monday?" (No school next Monday. So, they're due next next Monday.)

20180213

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

Astronomy 210, spring semester 2018
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.
"I love telescopes, and I always love understanding that large diameter equals more light gathering capability, Which is everything."

"How turbulence is what gives stars their 'twinkle.' I never knew it was because of disturbances stirring up the air in the atmosphere that caused a distorted view, which causes the twinkle we see."

"Light pollution--how sensitive telescopes are, and also due to personal experience--during the most recent eclipse I traveled to Oregon and went to a government research facility with a radio telescopes and we weren't allowed to even have our cell phones on due to the sensitivity of the telescopes."

"I found the whole spectrum of visible light interesting and very informative. Being that I had minimal to no clue as too what it was to begin with."

"That Earth's turbulence caused the twinkling in the stars--I thought they were just the flames flicking in the atmosphere."

"Effects of atmospheric winds on starlight."

"Each power of telescopes, especially to learn and read in detail about them. Also, being able to identify the different shapes and sizes of telescopes in class was very cool and interesting."

"This might sound dumb...but I didn't know how much manual labor was involved with operating and maintaining those big telescopes ("Keck in Motion"). I thought a person just sat behind a computer and pressed a button for everything."

"That Mercury and the moon being somewhat similar was interesting. I didn't think that they would have been."

"How the moon and planets such as Mercury have changed over time and the changes to the landscape."

"The large impact hypothesis--I have never heard/thought of anything like this happening and it blows my mind that it might have happened."

"I didn't know that the oceans dissolved carbon dioxide at the level it did; causing carbon dioxide levels in the atmosphere to lessen."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I found active optics and adaptive optics to be confusing, I don't understand the difference between the two."

"Active and adaptive optics--I just would like you to go over them in class."

"I don't really like telescopes."

"The oldest features of the moon and Mercury because I can't really tell what would be the oldest."

"The 'planetary smash-up' of two colliding planetsimals. Is this a hypothesis on how the moon was formed or Earth was formed? Or both?"

A large modern optical telescope in outer space would have images with better __________ than a comparable ground-based telescope.
brightness.   * [1]
resolution.   ******* [7]
magnification.   [1]
(None of the above choices.)   [0]
(Two of the above choices.)   ***** [5]
(All of the above choices.)   **** [4]
(Unsure/guessing/lost/help!)   *** [3]

Stars to appear to "twinkle" in the night sky because of...
"Stars appear to twinkle at night because the light from the stars travels through the air and causes the light to bend a certain way. This causes changes in the light from the stars that we see from Earth and us seeing the 'odd twinkle.'"

"Stars appear to twinkle due to the movement of air in the earths atmosphere. The light bends which causes some of the stars' light to be seen and some to not be as seen which causes the illusion of twinkling."

"Turbulence in the atmosphere that stir up the air and cause distorted astronomical viewing."

"This is due to turbulence in Earth's atmosphere. If the atmosphere is unsteady, then the stars will twinkle more."

"My guess would be light pollution?"

Identify how carbon dioxide enters and how it is taken out of Earth's atmosphere.
(Only correct responses shown.)
Enters atmosphere from: volcanoes [43%]
Taken out of atmosphere by: oceans [57%]

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) [43%]
Flat lava plains: middle [24%]
Craters on top of flat lava plains: youngest (formed most recently) [48%]

Identify the oldest (longest ago) to the youngest (most recent) features on Mercury.
(Only correct responses shown.)
Large crater basins: oldest (formed longest ago) [55%]
Lava-filled lowlands: middle [50%]
Long curving ridges: youngest (formed most recently) [67%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I only live about 15 minutes away from North County campus, but because I live out where there isn't much man-made light, there were about twice as many stars visible compared to when we viewed them on Thursday on campus. There were so many I had trouble finding some of the ones we'd looked at! What's the minimum amount of light that's capable of polluting the atmosphere enough to hide some stars? Is even a phone flashlight too much?" (For hard-core naked-eye observing, any amount of man-made light pollution is bad, as even a little would affect the faint stars of the Milky Way. Long time exposures help to reveal faint stars in photos, but even then the effect of light pollution also gets brightened as well. Phone flashlights aren't too much of a big deal, though those would have a big impact on temporarily ruining your night vision.)

"Can we go over in more detail the oldest to youngest parts of both Mercury and the moon?."

"A little confused about the youngest to oldest questions of the planets. The book just words it confusingly."

"Do you want students to bring anything to the star parties (other than people)?" (Just bring your love of astronomy (and any like-minded people as well).)

"I'm not quite understanding this material and need help."

"Why are the questions on our quizzes four points each and not two points each? :/"

20180212

Online reading assignment: optical instruments

Physics 205B, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students have a bi-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.


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.
"The two-lens ray tracing models, where the image from the first lens affects the image in the second lens. It wouldn’t make sense for these two to be separate entities, and this seems pretty straightforward."

"Angular size is the measure of how big something seems from your viewpoint. Angular magnification is the measure of how much larger the angular size of an object seems through a magnifier rather than with your naked eye. 25 cm is the near point, or the nominal closest distance an unaided eye can focus on."

"The difference between a telescope and a microscope. They both serve to make a object the right magnification for observation by the human eye, but do so in very different ways."

"There are various similarities between microscopes and telescopes, such as they both have focal objective lenses and eyepiece lenses to see the image. The similarities and differences also lie in the ray tracings, which I kind of don't understand."

"The distinction between ray tracings for microscopes and telescopes made sense to me. Being able to visualize it in the presentation helped. For microscopes the object is closer to the focal point and for telescopes it is really far away."

"Microscope and telescope both have two lenses. The objective takes the light from object, and creates a real image that becomes the object 2 for the eyepiece."

"Microscopes and telescopes both use converging lenses to make an object appear bigger but they differ in length in order to make a really small object seem big or a really far object seem close."

"For a microscope objective the object is placed close to the focal point and thus gives a very enlarged image. For a telescope objective the object is very far away, producing incoming rays that are essentially parallel."

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 will need some in class help with the new equations for microscope magnification and telescope magnification."

"The difference between microscopes and telescopes are a little difficult. I’ve had difficulty with ray tracings so I need more explanation on that."

"Since we are now studying angular magnification of compound microscopes, telescopes, and magnifying glasses we have to use different types of angular magnifications for each scenario. I am really confused as to use which equation for which scenario. I feel that if we go over some examples in class I'll have a better idea but right now I don't quite get it."

"I don't understand the microscope ray tracings and what they mean--definitely need help with that."

"I don't understand how the image from the objective becomes the object for the eyepiece."

"I'm having some trouble understanding the telescope eyepiece as well as the microscope eyepiece. This may however just be because I need some review on magnifications."

Identify the type for each of these lenses. (Only correct responses shown.)
Microscope objective: converging [82%]
Microscope eyepiece: converging [70%]
Telescope objective: converging [82%]
Telescope eyepiece: converging [70%]


Identify the ray tracing for each of these lenses. (Only correct responses shown.)
Microscope objective: ray tracing 2 [57%]
Microscope eyepiece: ray tracing 3 (or 4) [36%]
Telescope objective: ray tracing 3 (reversed) [9%]
Telescope eyepiece: ray tracing 3 (or 4) [36%]

For the microscope equation, 'L' is the distance between the objective and eyepiece lenses, and 'N' refers to the near point, which is assumed to be the nominal 25 cm value.

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.  **************** [16]
short; long.  ******** [8]
long; short.  ***** [5]
long; long.  [0]
(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.  ******* [7]
long; short.  ****************** [18]
long; long.  *** [3]
(Unsure/lost/guessing/help!)  ***** [5]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I have used a compound microscope in my microbiology class but the angular magnification equation was different there?" (The angular magnification equation for a microscope is just an approximation; and it turns out there are slightly different approximation equations. We're going to stick with the form given in the textbook.)

"Does the negative sign of the angular magnification equation indicate an upside-down image?" (sǝ⅄.)

"Can we do some examples of these angular magnification scenarios during class?"

"Can you please discuss more about angular magnification in respect to microscopes and telescopes?"

"I liked the optometry lesson the other day."

20180209

Astronomy current events question: neutron star merger brightening

Astronomy 210L, spring semester 2018
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!)
Daryl Haggard and Chris Chipello, "Neutron-Star Merger Yields New Puzzle for Astrophysicists" (January 18, 2018)
chandra.harvard.edu/press/18_releases/press_011818.html
NASA's Chandra X-ray Observatory recorded light from the merger of the two neutron stars GW170817/GRB170817A that appears to be unexpectedly:
(A) lacking neutrinos.
(B) cold.
(C) distorting space-time.
(D) brightening over time.
(E) made of antimatter.

Correct answer: (D)

Student responses
Sections 30679, 30680
(A) : 2 students
(B) : 1 student
(C) : 3 students
(D) : 31 students
(E) : 2 students

Astronomy current events question: laser-triggered mini-gamma ray bursts

Astronomy 210L, spring semester 2018
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!)
Emma Gallagher, "Queen's University Scientist Unlocks Gamma Ray Burst Secrets" (January 19, 2018)
https://www.qub.ac.uk/News/Allnews/QueensUniversityscientistunlocksgammarayburstsecrets.html
Researchers used __________ to reproduce miniature gamma-ray bursts similar to those observed in distant galaxies.
(A) lasers.
(B) cold fusion.
(C) computer simulations.
(D) dark matter.
(E) ultrasound.

Correct answer: (A)

Student responses
Sections 30679, 30680
(A) : 28 students
(B) : 2 students
(C) : 4 students
(D) : 3 students
(E) : 1 student

Astronomy current events question: the "Humanity Star" satellite

Astronomy 210L, spring semester 2018
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!)
News release, "FAQs" (ca. January, 2018)
thehumanitystar.com
Rocketlab recently launched "Humanity Star" into orbit, which will be visible to the naked eye in the sky for the next nine months until it: (A) creates an impact crater on the moon.
(B) docks with the International Space Station.
(C) burns up in Earth's atmosphere.
(D) depletes its batteries.
(E) refolds back into its cube.

Correct answer: (C)

Student responses
Sections 30679, 30680
(A) : 1 student
(B) : 9 students
(C) : 24 students
(D) : 3 students
(E) : 1 student

20180207

Online reading assignment: history of astronomy, telescope powers (SLO campus)

Astronomy 210, spring semester 2018
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 reviewing the history of astronomy, Kepler's and Newton's laws, and telescope powers.


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 ancient model of the universe to be very interesting. I was intrigued by Plato's idea that 'all motions in the heavens must be made up of combinations of circles moving at uniform rates.'"

"That we once had no idea that our Earth was moving and instead believed that it stayed still. I think this is interesting because we knew so little about the planet that we live on."

"How planets move. I always thought they moved in circular motions but found it fascinating that they move in ellipses."

"That planets move at different speeds at different parts of their orbits."

"I guess this isn't necessarily about the science itself, but I find the Church's and society's response to heliocentrism fascinating. I think that science and the institutions in charge (government/church) have a very cyclical relationship with a lot of current parallels to this, so it's very interesting to compare."

"That centuries ago people were able to calculate elliptical orbits and gravitational pull so interesting. Its fascinating because they accomplished all this without the use of computers or calculators"

"I think Newton's laws are interesting to me, especially the first law. The concept of a object staying in motion unless acted upon by another force was extremely cool to me when I initially learned about it."

"The information about Newton's cannon is very interesting to me as it is something that I have honestly never heard of before. The idea that eventually firing a projectile with an adequate level of speed (along with the other requirements mentioned) could cause it to then 'arc downwards' after traveling for a long enough distance that it would continue to orbit around the planet is blowing my mind. I suppose this is personally interesting to me simply because it presents an aspect of astronomy that I have never heard or thought of before, and thus changes the way that I view the world in a big way."

"Learning about telescopes and their differences, now I want a telescope."

"That the magnifying power of a telescope was not the most important power for a telescope to have."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Who discovered what, when, and for what existential or rational reason(s)."

"Whether or not certain astronomers were movers or disprovers. There is no clearly defined line which makes this a little hard to identify."

"The force laws, and motion laws and what they attempt to regulate is still pretty confusing for me. I don't really understand the difference between Kepler's second and third laws for example. I also don't have a super solid grasp on the telescope optics yet, but i think that a quick refresher in class would help with that."

"Basically all of the laws of motion were a bit hard to understand."

"I am finding the process of matching the descriptions of Newton's laws here on the survey with the laws presented in the presentation and in the textbook. The process of matching them doesn't seem as clear-cut as I imagine it should be for me after reading the material, and I would love to go over then in class to really get the foundation of each law. I suppose that this is personally confusing to me because this information is so new and thus it's confusing to recognize from the short options given in the survey what law really belongs where. Also, I feel like a lot of the information regarding the telescopes is going over my head despite my reading all of the slides provided. I think this is personally confusing to me only because I tend to learn concepts such as this better when I can have the real thing in front of me to really put everything into place."

"Kepler's laws confuse me because I'm just unsure what is trying to be explained."

"I was confused between Kepler's second and third law. If the closer planets go faster, then doesn't that already mean that the ones with the closer orbit to the sun go faster?"

"Kepler's laws and Newton's laws. It's a lot of information."

"Why was the Church so involved in astronomy? Did they believe space was an extension of heaven? or did they believe God made them (Earth) the center of the universe and did not want to believe the new scientific studies?"

"Anything and everything involving telescopes. I need clarification on this."

"What appeared to me most confusing to me was the chapter on the telescopes. There was a lot of terminology in the textbook and what helped decipher all that terminology was the online presentation pictures. Not that it was difficult to understand there is just so much to it."

When a planet is undergoing retrograde motion, over several nights it moves __________ with respect to the background stars.
east to west.   ******************* [19]
west to east.   *************** [15]
(Either of the above choices is possible.)   [2]
(Unsure/lost/guessing/help!)   ***** [5]

When a planet is undergoing prograde motion, over several nights it moves __________ with respect to the background stars.
east to west.   **************** [16]
west to east.   ******************* [19]
(Either of the above choices is possible.)   * [1]
(Unsure/lost/guessing/help!)   ***** [5]

Categorize each of Kepler's laws.
(Only correct responses shown.)
Kepler's first law: describes the shape of a planet's orbit. [88%]
Kepler's second law: describes the motion of a planet along its orbit. [90%]
Kepler's third law: describes the motion of a planet along its orbit. [80%]

Categorize each of Newton's laws.
(Only correct responses shown.)
Newton's first law: relates forces with changes in motion. [66%]
Newton's second law: relates forces with changes in motion. [68%]
Newton's third law: describes a property of forces. [61%]

The __________ power of a telescope depends on the: (Only correct responses shown.)
light-gathering: diameter of the primary lens/mirror [46%]
resolving: diameter of the primary lens/mirror [63%]
magnifying: both the focal lengths of the primary lens/mirror and eyepiece: [24%]

The least important feature to consider when purchasing an optical telescope is the __________ of its images.
brightness.   ********** [10]
resolution.   ** [2]
magnification.   *************************** [27]
(Two of the above choices.)   ** [2]
(Unsure/lost/guessing/help!)   [0]

Briefly explain your answer for the least important feature to consider when purchasing an optical telescope.
"Higher magnifying power doesn't mean that it will show you more detail. The primary function of a telescope is to gather light to make it appear brighter."

"The brightness and resolution need to be on point to clearly view anything. Magnification is not as important of a characteristic if you start with a poor image."

"Magnification just blows up whatever image your brightness and resolution got you. Blowing up a blurry picture just gives you a bigger blurry picture."

"Magnifying power is the least important feature to consider when purchasing an optical telescope because the mere act of making something larger will be rendered almost meaningless if the other (more important) features such as resolution and brightness are not adequate enough to complement the strength of its magnification abilities. As said in the presentation, just making the image bigger alone can't make it appear any clearer or brighter."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Who do you think had the biggest impact (out of all the great astronomers listed in the book, or otherwise) on the scientific revolution?" (The physicist in me would say Newton, as he was the first to ever formulate a set of laws that explains what is observed in nature, but I certainly admire Kepler, as he was willing to let go of preconceived notions once he made an honest, open assessment of Tycho's data--that to me is the real spirit of science.)

"I am having a hard time understanding all of the physics behind what we are learning in our textbook. Are there any sources that I should read to brush up on my physics or would it be wiser for me to read through the textbook a bit confused and come to class with more questions? I feel like once I miss one of the things in the textbook it is going to have a snowball effect on my questions though." (In class I'll emphasize the descriptive, conceptual part of physics that you'll be ultimately responsible for on the quizzes and exams, so don't stress out about having to know everything about all the things. If you're still confused after class, then by all mean ask or e-mail me questions.)

"Will the questions about Kepler's laws and Kepler's laws be on the quizzes? (Yes, similar to those in the question packet.)

"What is the difference between forces and changes in motions?" (It's easier to talk about motions first, whether it is stationary, or moving with a certain speed and direction. Anything that would change the motion of an object (starting it to move, stopping it from moving, changing its speed and/or direction) is defined as a force: gravity, air resistance, friction, kicking, hitting, lifting, etc.).

"Isn't the light-gathering power supposed to be defined by the primary lens/mirror's total area? On the quiz the only option is for diameter." (In a strict sense, yes, but if you have the diameter of a primary lens or mirror, you can calculate its area; so bigger diameters correspond to bigger areas.)

"What are some tips to remembering which telescope gives which effect?" (I'll try to help you make a cheat sheet for this in class.)

This section is pretty boring no offense." (Eh, it's like that for some people.)

"I'm having trouble understanding what a radio telescope is and what it does." (It is designed to detect natural long-wavelength forms of light we can't visibly see, given off by low temperature sources, such as the type of gas and dust clouds that stars and planets form from. Cell phones, radio stations, and satellite TV are all man-made sources of that same long-wavelength type of light, which radio telescopes need to be kept away from.)

"Do you think that Galileo would have made even more discoveries if he had not been locked away?" (Well, if he wasn't persecuted for his scientific findings, then he wouldn't have all that science-y street cred he has today.)

Favorite thing about space?" (Right now this week, it would be the "Starman" driving the Tesla Roadster that was just launched by Space X.) "

Online reading assignment: corrective optics, magnifiers

Physics 205B, spring semester 2018
Cuesta College, San Luis Obispo, CA

Students have a bi-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.
"Using a two-lens system you can correct for common visual effects. Diopters can be (+) for converging lens and (–) for diverging lens."

"Diverging lenses are used to correct for myopia and that converging lenses are used to correct for hyperopia."

"For two lens systems, the image produced from the first lens is treated as the object for the second lens. I also understand a little bit about how optometrists prescribe corrective glasses to people and the difference between focal length and diopters. Finally, I have a decent understanding of angular magnification works by relating the distance away from the object to the angle at which you are seeing it."

"If you can't see both close and far things, get bifocals."

"I understand what angular size and magnification are. I also get that a 'magnifier' focuses rather than magnifies."

"The two-step model is used in corrective vision as the contact lenses produce a virtual intermediate image at a distance that the eye can focus on. This becomes object 2 for the second lens--the eye--as it turns it into a real image on the retina. If the far point is less than ∞ and/or near point is greater than 0.25 m, then an individual needs corrective optics. Bifocals for have converging lenses for myopia (looking straight) and diverging lenses for hyperopia/presbyopia (looking down for reading)."

"That 'magnifiers' aren't really magnifying, they're playing with angular magnification. By using a magnifying glass you aren't making an object bigger but by placing the object at the focal point of the lens in creates a virtual image that makes it look bigger/closer to you."

"I understood the process of why two lenses are sometimes needed. The first lens produces an intermediate image that the second lens then has to make into the final product. This reminded me of polarized vs non polarized light going through filters--if polarized light passes through two filters, the way it passes through the first directly affects the way it presents through the second filter."

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.
"This is all relatively confusing, as it is a lot of new information to take in. I need in-class reinforcement and repetition as usual :)"

"The contacts/glasses stuff confused me. From the slides I was uncertain how to contact the thin lens equation with the two step model."

"Some parts at the end of the online presentation were a bit confusing. The last few pictures didn't help."

"Angular magnification."

"I found the concept of 'projecting to infinity' confusing. It is hard to comprehend such an abstract idea."


In general, a converging lens will produce virtual, upright images located __________ the original object.
closer than.   ****** [6]
at the same distance as.  ** [2]
farther than.  ******************** [20]
(Unsure/lost/guessing/help!)  * [1]


In general, a diverging lens will produce virtual, upright images located __________ the original object.
closer than.   ******************** [20]
at the same distance as.  ** [2]
farther than.  ****** [6]
(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 [72%]
Glasses/contacts to correct for hyperopia: converging [72%]
Glasses/contacts to correct for presbyopia: converging [31%]
Magnifying lenses: converging [70%]

State the units of refractive power for lenses, and briefly describe the relationship between refractive power P and focal length f.
"The units of refractive power are P, in units of diopters. This is the inverse of the focal length f, which is measured in meters."

"I have no idea."

Explain the difference between the two types of magnification, m and M.
"Angular magnification M is a value that describes how much larger the angular size of an object appears to be through a magnifier compared to an unaided eye. Meanwhile the linear magnification m is the ratio of image length to object length measured."

"m = linear magnification, while M = angular magnification which tells you how much larger the angular magnification is when looking at an object through a magnifier."

"Unsure."

A nominal, relaxed eye is set to focus on objects located at:
+∞.  *** [3]
+25 cm (at your near point).  ****** [6]
+f (at the focal point of the lens).  [15]
(Unsure/lost/guessing/help!)  ***** [5]


Bringing something closer biggifies it. BIGGIFIES.

If an object is brought closer to your eye, its angular size will:
increase.  *********************** [23]
decrease.  ***** [5]
remain unchanged.  * [1]
(Unsure/lost/guessing/help!)  [0]

When a converging lens is used as a simple magnifier, the object is placed at a distance do = __________ in front of (to the left of) the lens.
+∞.  * [1]
+25 cm (at your near point).  ******** [13]
+f (at the focal point of the lens).  ******** [8]
(Unsure/lost/guessing/help!)  ******* [7]



The ray tracing that best matches when a converging lens is used as a simple magnifier is:
#3.  ******** [8]
#4.  ************** [14]
(Unsure/lost/guessing/help!)  ******* [7]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Can we talk about angular magnification?"

"It seems like for presbyopia you would need both types of lenses? But isn't presbyopia similar to hyperopia?" (Yes, presbyopia is basically age-onset hyperopia; even if you can see near now, you will eventually lose that ability as you get older. So if you don't need glasses/contacts now, you'll need reading glasses if you live long enough. However, if you have glasses/contacts to be able to see far (myopia or nearsightedness), you'll need bifocals to also see near when you get old. (If you're still young and have glasses/contacts to be able to see near (hyperopia), you'll just need stronger reading glasses to see near when you get old.)

"I am sorry, I am not there yet. My answers look crazy. Trying to catch up already."

"I feel like everything seems to straightforward in class but then I get to these assignments and I feel so lost :("

"Thank you for all of your hard work in simplifying the text's material on your website (and making it fun)."

"My schedule right now is making things very hard to learn outside of class. The downside to doing the lecture oupside of class class is it can be hard to find the time or space to do this."

"Why does the object's height not mater when we did the ray tracings in lab? Won't that change the distance that the image is from the lens?" (In the thin lens equation (and for ray tracings), the object distance and image distance only depend on each other (and the focal length) of the lens:

(1/do) + (1/di) + (1/f),

and the object height and image height do not affect the object distance and image distance. However, the object height and image height are related to the object distance and image distance:

(hi/ho) = –(di/do).

Graphically, making the object arbitrarily large or small on a ray tracing just makes the resulting image proportionally large or small as well (stretching or scrunching the vertical dimensions of your ray tracing), but the object distance and image distance (the horizontal dimensions of your ray tracing) are unaffected.)