20130228

Astronomy quiz question: telescope funding

Astronomy 210 Quiz 3, spring semester 2013
Cuesta College, San Luis Obispo, CA

Based on being able to detect its wavelength, and cost-effectiveness of location, which telescope should be funded?
(A) A near-infrared telescope on an aircraft (45,000' altitude).
(B) A gamma ray detector in Antarctica (8,000' elevation).
(C) A (TV) radio telescope in space (above 500,000' altitude).
(D) An ultraviolet detector in the Mojave desert (5,000' elevation).


Correct answer (highlight to unhide): (A)

Gamma rays, ultraviolet, and near-infrared cannot be detected at sea level (the bottom edge of the graph), due to absorption of these wavelengths by the atmosphere. Some gamma rays and ultraviolet may be detected at high elevations, but a near-infrared telescope on an aircraft would have a much greater altitude, and receive much more signal than high-elevation gamma rays and ultraviolet detectors. A radio telescope would work in space, but would work just as well on the ground for much less cost than a near-infrared telescope on an aircraft. So while the near-infrared telescope on an aircraft and a radio telescope in space would both be able to detect its wavelength, funding a radio telescope in space is not a very effective use of money, so out of these four choices, the near-infrared telescope on an aircraft is the best choice that should be funded.

Section 30674
Exam code: quiz03nPmP
(A) : 23 students
(B) : 7 students
(C) : 4 students
(D) : 5 students
(No response: 1 student)

Success level: 79% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.67

Section 30676
Exam code: quiz03sPmP
(A) : 27 students
(B) : 10 students
(C) : 14 students
(D) : 2 students

Success level: 66% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.55

Astronomy quiz question: comparing telescope magnifying powers

Astronomy 210 Quiz 3, spring semester 2013
Cuesta College, San Luis Obispo, CA

Consider two Orion™ reflector telescopes, which have mirrors with different diameters and focal lengths. The StarBlast®(*) telescope has a larger diameter and longer focal length mirror than the SkyScanner®(**) telescope. If a 20 mm focal length eyepiece is used with both telescopes, the __________ telescope will have more magnifying power.
(A) StarBlast®.
(B) SkyScanner®.
(C) (There is a tie.)
(D) (More information is needed to determine this.)

(*) "Orion™ StarBlast® 4.5 Astro Reflector Telescope, 114 mm aperture, 450 mm focal length," bit.ly/XXpRpM.
(**) "Orion™ SkyScanner® 100 mm TableTop Reflector Telescope, 100 mm aperture, 400 mm focal length," bit.ly/YyqFA1.

Correct answer: (A)

The magnifying power of a telescope is the focal length of the primary mirror (or lens) divided by the focal length of the eyepiece. Since the same eyepiece is used by both telescopes, the telescope with the longer primary mirror focal length will have more magnifying power.

Section 30674
Exam code: quiz03nPmP
(A) : 18 students
(B) : 8 students
(C) : 4 students
(D) : 0 students

Success level: 63% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.58

Section 30676
Exam code: quiz03sPmP
(A) : 18 students
(B) : 10 students
(C) : 14 students
(D) : 2 students

Success level: 45% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.18

Astronomy quiz question: adaptive optics

Astronomy 210 Quiz 3, spring semester 2013
Cuesta College, San Luis Obispo, CA

Adaptive optics improves the resolution of telescope images by using a computer to rapidly:
(A) change the humidity inside the tube.
(B) trigger a laser to heat up the atmosphere.
(C) combine the light collected by several connected telescopes.
(D) adjust the shape of the mirror.

Correct answer: (D)

Distortions in images caused by atmospheric turbulence can be removed in real-time by using a computer to reshape the (secondary) mirror such that a reference star (or a laser beam) within the field of view has a point-like shape. Response (C) is interferometry (which also improves the resolution of telescope images).

Section 30676
Exam code: quiz03sPmP
(A) : 0 students
(B) : 0 students
(C) : 17 students
(D) : 27 students

Success level: 64% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.55

Astronomy quiz question: adaptive optics

Astronomy 210 Quiz 3, spring semester 2013
Cuesta College, San Luis Obispo, CA

Adaptive optics is used in modern optical telescopes to improve:
(A) light-gathering power.
(B) resolving power.
(C) magnifying power.
(D) the amount of radiation transmitted through the atmosphere.

Correct answer: (B)

For large ground-based telescopes, their resolving power is limited by atmospheric turbulence, which distorts and "twinkles" the stars. Using adaptive optics to shape the mirror to compensate for these distortions will improve the resolution of images obtained by ground-based telescopes.

Section 30674
Exam code: quiz03nPmP
(A) : 2 students
(B) : 17 students
(C) : 3 students
(D) : 8 students

Success level: 58% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.68

Astronomy quiz archive: telescopes

Astronomy 210 Quiz 3, spring semester 2013
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz03nPmP


Section 30674
0- 8.0 :
8.5-16.0 : ***** [low = 8.0]
16.5-24.0 : *******
24.5-32.0 : ********* [mean = 25.7 +/- 8.1]
32.5-40.0 : ******* [high = 40.0]


Section 30676, version 1
Exam code: quiz03sPmP


Section 30676
0- 8.0 :
8.5-16.0 : ******** [low = 10.0]
16.5-24.0 : ****************** [mean = 23.0 +/- 6.7]
24.5-32.0 : ***********
32.5-40.0 : ******* [high = 36.5]

20130226

Online reading assignment: double-slit interference

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

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on double-slit interference.

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 found Thomas Young's experiment very interesting. I liked this experiment, because it reminds me of one done on electrons, and how those act. I know that this is kind of unrelated, but it is based on how the electrons behave when shot through two slits just like the light experiment."

"I thought it was really neat how Thomas Young was the first person to be able to measure the wavelength of light by using a double slit experiment."

"I found that maxima is the location were two sources interfere constructively, and minima is the same definition, but where destructive interference occurs."

"Nothing because I don't understand how this information applies to anything."

"The idea of light waves canceling is weird, but I like that. I like the real world example of water waves."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I was having trouble understanding why the light that comes out of the two slits starts in phase but ends up being out of phase."

"I don't think Young's experiment could be written any more confusingly than in the book."

"Where those waves from the double slit are constructive or destructive as theta increases."

"How ∆l = d·sinθ."

"This section doesn't seem too hard to grasp."

"I am confused on all of this. Could use some explanation in class not solely inclusive of problem-solving."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I don't understand for waves from a double-slit how the rays converge to one point. Why are they not constantly parallel from the beginning?" (They can't be parallel if they are to eventually meet at the same location. But if that location is very far away, and the space between the two slits is relatively small, then the two rays can be said to be approximately parallel.)

"Sometimes the animated slides can be more confusing then if they weren't animated. they may be a bit to fast to read and comprehend before the animation changes." (Well, it's a compromise between being too slow, and waiting a long time to see what happens, and being too fast, and not being able to see each step. At least the animations loop continuously.)

"I got a little off-topic and side-tracked while reading when I came across the image of a cross-section of a CD. Not very much of it made sense. Could we possibly go over this in class briefly? Just interested in how it really works with the 'pits' in the reflective layer." (The bumpy concave/convex "pits" scatter laser light in all directions, while the flat "land" portions will reflect laser light back to the detector for a standard CD-ROM. The length and spacing of the both the "land" and "pit" portions that encode binary data.)

Online reading assignment: Kirchhoff's laws (SLO campus)

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

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on Kirchhoff's laws.

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 find the section on star distances interesting because stars are SO FAR AWAY."

"The whole idea of measuring the distances in the stars was pretty interesting. It seems so simple, just basic trigonometry, but it is so much more complex."

"I thought it was interesting to learn about apparent magnitude, because that's something that I can relate to by just looking at the sky at night with my own eyes."

"Knowing that there is an actual name for the wavelengths that lower or raise in volume when they become closer or farther (Doppler effect). This is interesting because I didn't think there was an actual specific word for it."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"How did I never think to do a Doppler effect video for science class in high school?"

"The Doppler effect is confusing. I get it kind of, but I can never remember which color goes with receding and which one goes with approaching."

"Spectra."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I have to admit that I haven't been studying or reading for the last couple of weeks. That is definitely why I scored so low on Quiz 2. I do not feel good about it, as I really do like astronomy. And you seem to be an awesome educator/human. Much respect." (Word. But yes, get on studying more for this class.)

"Can we not have a 'celebration of learning' today?" (Party-pooper.)

"This class is fun but it's very difficult so far. Can you make it easier somehow?" (Come see me just before/after class, or during office hours (make an appointment if you can't come during the regularly-scheduled office hours), or e-mail. Let's find out what you're doing right (or wrong) in studying for this class, and see how you can best study to improve your standing in this course.)

"I HATE the quizzes. I feel like I know all of the material, then I bomb the quizzes...how do I not bomb the quizzes?" (Go through the unused flashcard questions. More than half of the quiz questions so far are from the flashcard question packets.)

"Please explain what an isotope is so it makes more sense in my brain! Still throws me off. Not sure how it relates to the quantum leaps, photon absorbing, and changing orbits." (Eh, it's not really related, so you don't need to know about isotopes for this course. That said, isotopes are a group of atoms that all have the same number of protons (iso = "equal," tope = "place" on a periodic table chart), but have different numbers of neutrons. Some helium atoms have two protons and two neutrons, but some helium atoms have two protons and only one neutron. These different forms of helium are said to be isotopes.)

Astronomy current events question: final moments before type II supernova

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

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Ron Cowen, "Astronomers Catch Rare Glimpse of a Star's Final Moments," February 6, 2013
http://www.nature.com/news/astronomers-catch-rare-glimpse-of-a-star-s-final-moments-1.12383
Astronomers at the Weizmann Institute of Science in Israel have observed the behavior of a star before undergoing a recent type II supernova explosion, from:
(A) earlier images taken of the same region of sky.
(B) neutrino emissions in deep underground mines.
(C) pulsar timing variations.
(D) radioactivity fluctuations.
(E) gravitational lensing.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 23 students
(B) : 1 student
(C) : 10 students
(D) : 15 students
(E) : 2 students

Astronomy current events question: Curiosity rover night photos

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

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Guy Webster, "Mars Rover Curiosity Uses Arm Camera at Night," January 24, 2013
http://www.nasa.gov/mission_pages/msl/news/msl20130124.html
NASA's Mars rover Curiosity used its arm camera to take photos at night, in order to:
(A) watch a sand dune avalanche.
(B) overwrite faulty data in a memory bank.
(C) determine local light pollution conditions.
(D) use up excess energy stored from its solar panels.
(E) detect minerals that glow under ultraviolet light.

Correct answer: (E)

Student responses
Sections 30678, 30679, 30680
(A) : 0 students
(B) : 0 students
(C) : 1 student
(D) : 2 students
(E) : 48 students

Astronomy current events question: "next door" Earth-size planets?

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

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Michele Johnson, "Kepler Data Suggest Earth-size Planets May Be Next Door," February 6, 2013
http://www.nasa.gov/mission_pages/kepler/news/kepler-data-suggests-earth-size-planets-next-door.html
Astronomers at the Harvard-Smithsonian Center for Astrophysics estimate that Earth-size planets may be "next door," based on analyzing data from NASA's Kepler space telescope of planets orbiting:
(A) stars about to undergo type II supernova explosions.
(B) our sun, out beyond Pluto.
(C) red dwarf stars.
(D) sun-like stars.
(E) massive stars.

Correct answer: (C)

Student responses
Sections 30678, 30679, 30680
(A) : 1 student
(B) : 3 students
(C) : 40 students
(D) : 6 students
(E) : 1 student

20130225

Online reading assignment: Kirchhoff's laws (NC campus)

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

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on Kirchhoff's laws.

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 think the emission spectrum is pretty cool. I like the fact that you can't see the full continuous spectrum, that through the emission of the gas, there are only certain things you can see on the spectrum."

"I liked to officially read in a textbook about the Doppler Effect. I had first learned about this from The Big Bang Theory, the TV show!"

"The different sound wavelengths of when the car moves 'towards' or 'away' can either be squished or stretched, just like light from moving stars."

"I find it very interesting that light can be split up into a rainbow."

"Hearing about how parallax is used to measure the distance of the sun from planets--especially hearing about how the best time to do this is when Venus is eclipsing the sun since I got to see the transit of Venus this summer."

"How astronomers are able to calculate the amount of each element present in a star and how those elements are identified."

"I thought 'spectrum' was interesting because I always heard that word and never really understood what it meant."

"I found the different spectra interesting because I never really took time to notice the differences before when I'd see something with a spectrum until now."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Can we talk about different spectra more? They are hard to tell apart in certain visuals."

"Trying to imagine light as a photon and a wave can be a little mind-boggling."

"What I found confusing was the 'redshift' and 'blueshift'--how do you know when it's a red or blue shift?"

"The Doppler effect is confusing. I can't understand why sound waves seem to compress traveling out ahead of an object and then stretch out traveling away behind an object."

"Absolute magnitude and apparent magnitude. It seems like they should be simpler than how the book describes it. But I'm not sure."

"I'm still working on understanding how absorption spectra and emission spectra are formed, and how these lines form a 'fingerprint' for each element."

"I found confusing how the parallax is measured."

"How to distinguish the types of spectrum in the pictures was confusing. I was looking for rainbows."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Absolute magnitude is the apparent visual magnitude that star would have if it were 10 pc away, what does 'pc' stand for?" (A parsec, which is 3.26 light years, or the distance light would travel in 3.26 years.)

"I found the triangulation of stars to be a little confusing. The only reason for this is that I hate math. I did all the math that I needed to so that I can transfer, and I don't really want to do a whole lot more. It wasn't terribly confusing, math just freaks me out." (Teaching math freaks me out, too. However, the focus in this course is on comparing which variables affect certain quantities, and not on actually calculating values for those quantities.)

"Do you like physics or astronomy more?" (To me, they are the same thing. However, I enjoy teaching astronomy to non-science majors more than teaching physics to engineers.)

"Star night?" (Cancelled as of 5:30 PM that night due to party cloudy conditions. Yes, I know that the clouds cleared, but I had to make the call based on what I saw.)

"Why don't you like The Big Bang Theory?" (The Big Bang Theory makes fun of nerds and geeks. Shows like Community has fun with nerds and geeks.)

"Starting to get the hang of this class finally." (Keep doing what you're doing (that is, going through the unused flashcard questions.)

"Can we do more flashcard questions in class?" (As time allows in class, but go through the unused flashcard questions for homework.)

"I love how we spot check each other in-class activities and flashcards, can we start spot checking each other on quizzes too? :)" (I don't think you'd want to do that, if I get to choose which students you work with on the quizzes.)

"How does light waves have anything to do with the Doppler effect?" (All types of waves emitted from moving objects (whether sound, or light) experience the Doppler effect.)

"Do you have a system or algorithm with these group rotations? Been grouped with some people multiple times already while a bunch of others not at all." (Each group is meant to be comparable mixture of students in overall course ranking. If you haven't been grouped with certain students (yet), you are probably very close to them in class standing so far in this course.)

20130224

Online reading assignment: interference

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

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on interference.

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.
"If you don't plug stereo cords in their appropriate color inputs the waves as a result will oscillate out of phase and not align which why it won't produce a sound."

"How switching polarities of a speaker can in theory silence the sound, but in reality just reduce the sound."

"How destructive and constructive waves work, my brothers are both in bands and when they are setting up the amps I always wonder why so many cords are necessary."

"It's interesting to think about the application of sound waves and how they work and can interfere with each other. I DJ and you deal with that all of the time."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"The use of the equations for interference. I am getting lost with the equations."

"I found the equations for constructive and destructive interference confusing! We should use them in an example in class!"

"I was a little confused on what exactly constructive and destructive interference were. Is constructive when sound is produced and destructive silence?"

"What exactly happens when two speakers are set up so the sound waves are perfectly destructive? They create silence?"

"I read the portion about constructive and deconstructive interference, and I do not understand them through the text. I would benefit from some for visual examples in the class to distinguish the two apart."

"Nothing too confusing."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Are we going to listen to speakers in class?" (Oh, yes.)

"So are we doing a lab with sound soon?" (No, but you will have two labs with interfering light waves.)

"If two waves are coherent, do they create constructive interference, if they travel the same distance?" (Yes, provided that they also start in phase from their sources.)

20130223

Presentation: electric forces and fields

Look at this van de Graff generator exerting attractive and repulsive forces on these soap bubbles. Just look at it. (Video link: "Static Electricity and Bubbles!")

While we will quantify how charges exert electric forces on other charges, consider the philosophical problem of why charges are able to exert electric forces on other charges, without touching, across empty space. This is the action-at-a-distance problem. We are going to "solve" this problem in this presentation--well, sort of--and much later will only be able to completely "solve" the action-at-a-distance problem near the end of this semester by introducing the concept of quantum electrodynamics.

In this presentation we will discuss two models of how charges exert electric forces on other charges.

First, a "direct" model of electric forces.

By convention we label the two charges that exert forces on each other as "source" and "test" charges, where the source charge q1 is said to be exerting a force on the test charge q2. This force is attractive if the source charge and test charge have opposite signs, and repulsive if the source charge and test charge have the same sign.

Coulomb's law quantifies the magnitude of the force that a source charge exerts on a test charge, separated by a distance r. Note that the signs of the charges do not matter when calculating the magnitude of the force, and that the constant k handles unit cancellation and conversion to express the force with the proper units of newtons.

Second, an "indirect" or two-step model of electric forces.

Here the convention is to label the source charge and test charge as Q and q, respectively. Instead of the source charge Q directly exerting a force on the test charge q, in this two-step model, the source charge Q is said to create an electric field everywhere around it, and it is this electric field that exerts a force on a test charge q.

Let's focus on the first step of this two-step model. The source charge Q creates an electric field everywhere around it. The magnitude of this electric field can be calculated for a location at a distance r from the source charge, and has units of newtons per coulomb (N/C). The direction of this electric field depends on the sign of the source charge Q: if the source charge is positive, the electric field vectors point outwards from it; if the source charge is negative, the electric field vectors point in towards it.

An electric field is depicted as filling in all space surrounding a source charge, and is drawn as field lines that point outwards from a positive source charge, and point in towards a negative source charge.

Now what? If there is another charge anywhere in the presence of an electric field, this electric field will exert a force on the test charge q. Note that this is a vector equation, where the force F (magnitude and direction) exerted on the test charge q is the test charge q multiplied by the electric field E (magnitude and direction) at the test charge's location. Since the test charge q could be positive or negative, then the electric force exerted on it could have the same or opposite direction as the electric field lines.

Here, from before, we show the electric fields filling in all space surrounding a positive or a negative source charge. Putting a positive test charge in the presence of these electric fields will cause an electric force to be exerted along a field line, while putting a negative test charge in the presence of these electric fields will cause an electric force to be exerted in the opposite direction of a field line. (In any case, as a check the direction of the force on any source charge q should be attractive or repulsive depending on whether it has the opposite or same sign as the source charge Q.)

So if using Coulomb's law in the direct model of calculates the electric force a source charge exerts on a test charge, why do we need a two-step model of a source charge generating a field, and this field exerting an electric force on a test charge?

Here in this excerpt from Star Wars Episode IV: The Empire Strikes Back (Lucasfilm/Twentieth Century Fox, 1980), Luke Skywalker is trying to grab his lightsaber, which is just beyond is reach. He could use the "force" to pull his lightsaber, but this brings up the philosophical problem of how a force of one object on another can be exerted across empty space.

Instead, let's reinterpret this in terms of the two-step field model. Luke goes into a trance, and let's say that he is generating some sort of field around himself (as Obi-Wan Kenobi explains: "...an energy field created by all living things. It surrounds us and penetrates us; it binds the galaxy together"). This field spreads out from and surrounds Luke, and it is this field that exerts a force on the lightsaber, pulling it out of the snowbank. Mayhem ensues.

So now we've "solved" the action-at-a-distance problem here by discussing a field as occupying the empty space surrounding and between the source object (Luke) and the test object (the lightsaber). (Perhaps, then, Luke is really using the "Field," and not the "Force" in the Star Wars universe.) And we put "solved" in quotes because this really recasts the philosophical action-at-a-distance problem as a philosophical question of what exactly is a field (and is it really generated by and surrounds a source object)? In a subsequent presentation near the end of this semester we will explain the physical nature of what a field is, but for now we will merely take an electric field as a given in our two-step model of how charges exert electric forces on other charges.

In this discussion we only considered the force exerted by a single source charge on a test charge, or the field generated by a single source charge. Later in class we will go through more complex situations where there may be multiple source charges, each exerting forces on the same test charge (thus requiring us to determine the net force on the test charge); or multiple source charges, each creating an electric field at the same location in space (thus requiring us to determine the net electric field at that location). So be sure to brush up on one-dimensional vector addition, as discussed last semester.

So remember, may the field be with you...

20130222

Astronomy quiz question: August 2017 partial/total solar eclipse in St. Louis, MO

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

In August 2017, observers in different neighborhoods of St. Louis, MO will either observe a partial solar eclipse or a total solar eclipse[*], depending on whether they are located in the moon's __________ or __________, respectively.
(A) negative shadow; penumbra.
(B) negative shadow; umbra.
(C) penumbra; negative shadow.
(D) penumbra; umbra.
(E) umbra; negative shadow.
(F) umbra; penumbra.

[*] eclipse2017.org/2017/maps/cities/STL.htm.

Correct answer: (D)

An observer in the moon's penumbra will see a partial solar eclipse, while an observer in the moon's umbra will see a total solar eclipse. (The "negative shadow" refers to the antumbra of the moon.)

Section 30674
Exam code: quiz03Ne3v
(A) : 4 students
(B) : 4 students
(C) : 0 students
(D) : 14 students
(E) : 1 student
(F) : 7 students
(No response: 1 student)

Success level: 47% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.23

Section 30676
Exam code: quiz02Sl1v
(A) : 5 students
(B) : 4 students
(C) : 8 students
(D) : 15 students
(E) : 5 students
(F) : 5 students

Success level: 41% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.73

Astronomy quiz question: Copernicus' model of planetary motion

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

Copernicus' model explained the retrograde motion of a planet by:
(A) having it orbit at a different speed than Earth's orbit around the sun.
(B) moving it on a circle that itself moves around Earth.
(C) using elliptical instead of circular orbits.
(D) disregarding parallax.

Correct answer: (A)

Copernicus' heliocentric model of planetary motion features Earth and the rest of the planets orbiting the sun, with the other planets orbiting at different speeds such that retrograde motion is observed when Earth is laps (or is lapped by) a planet. Response (D) describes Ptolemy's geocentric model of planetary motion.

Section 30676
Exam code: quiz02Sl1v
(A) : 15 students
(B) : 9 students
(C) : 18 students
(D) : 0 students

Success level: 40% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.64

Astronomy quiz question: Ptolemy's model of planetary motion

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

Ptolemy's model explained the retrograde motion of a planet by:
(A) disregarding parallax.
(B) moving it on a circle that itself moves around Earth.
(C) using elliptical instead of circular orbits.
(D) having it orbit at a different speed than Earth's orbit around the sun.

Correct answer: (B)

Ptolemy's geocentric model of planetary motion features Earth at (or very near) the center of a circular deferent, along which has a planet moving along a circular epicycle. Response (D) describes Copernicus' heliocentric model of planetary motion.

Section 30674
Exam code: quiz03Ne3v
(A) : 1 student
(B) : 14 students
(C) : 7 students
(D) : 9 students

Success level: 48% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.68

20130221

Astronomy quiz question: Kepler's laws

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

Kepler developed laws that:
(A) form the basis of the scientific process.
(B) explain the cause of ocean tides.
(C) describe the motion of planets around the sun.
(D) relate the motion of a body to the forces acting on it.

Correct answer: (C)

Based on Tycho Brahe's data, Johannes Kepler formulated three laws to describe different aspects of how planets move around the sun.

Section 30674
Exam code: quiz03Ne3v
(A) : 2 students
(B) : 1 student
(C) : 25 students
(D) : 3 students

Success level: 82% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.18

Astronomy quiz question: Tycho's observations

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

Tycho made observations that:
(A) Earth could not be the center of motion in the universe.
(B) disproved the heavens were perfect and unchanging.
(C) heavenly objects move on circular paths at constant speeds.
(D) Venus goes through a full set of phases.

Correct answer: (B)

Tycho Brahe used parallax to determine the distance of celestial objects. He observed the sudden appearance and dimming of a new star (supernova SN 1572) that had zero parallax, which he interpreted as being located in the heavenly sphere of stars, which refuted Aristotle's first principle argument that the heavens were perfect and unchanging.

Section 30676
Exam code: quiz02Sl1v
(A) : 14 students
(B) : 19 students
(C) : 3 students
(D) : 6 students

Success level: 49% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.64

Astronomy quiz archive: eclipses/history of astronomy

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

Section 30674, version 1
Exam code: quiz03Ne3v


Section 30674
0- 8.0 :
8.5-16.0 : ******* [low = 11.0]
16.5-24.0 : ********** [mean = 22.8 +/- 6.7]
24.5-32.0 : ***********
32.5-40.0 : *** [high = 36.0]


Section 30676, version 1
Exam code: quiz02Sl1v


Section 30676
0- 8.0 : **** [low = 0.0]
8.5-16.0 : **********
16.5-24.0 : ***************** [mean = 19.7 +/- 7.7]
24.5-32.0 : ********
32.5-40.0 : **** [high = 33.0]

20130220

Online reading assignment: atmosphere problems, quantum leaps, sun's outer layers (SLO campus)

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

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on problems caused by the atmosphere for telescope observing, quantum leaps, and the sun's outer layers.

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 reasons behind where astronomers place telescopes and why there have to be certain conditions, in order to have the maximum output from these telescopes and observatories."

"I enjoyed learning about turbulence in the sky, and how we live at the bottom of an ocean of air."

"That the speed of light was actually the speed of all electromagnetic radiation."

"Ultraviolet and x-ray telescopes have observed other stars having similar layers like our sun does. This is interesting to me because I tend to forget that our sun is star, so when I do think about it, it makes sense that other stars are layered as well."

"I found it very interesting that the ancient Egyptians, with the naked eye, perceived the sun as having wings and fire-spitting cobras."

"If I were floating in space with my friend and tried to talk to her she could not hear me, but if I flashed a light at her she could see it. This is because light waves can travel in a vacuum and sound waves can't."

"Well, I've only read the summary section so far, but I am more interested so far in reading about the sun's chromosphere than anything else."

"How the sun itself can have different temperatures on its surface itself like Earth, for example. Different areas can be warmer or colder."

"The phenomenon of convection and the example they gave with the hot coffee and cool creamer was interesting to me because I have witnessed that process through a cup of coffee before but did not really think much about it. Now that I know what convection is and how it works that will make drinking coffee a little more interesting."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I find it confusing to remember the different parts of the telescope and what is all needed. I think the most difficult part for me is figuring out what depends on what parts for light-gathering power or magnifying power."

I don't understand why electrons make quantum leaps. This type of information takes more than me simply reading a textbook to understand, because it is not something I can really visualize happening."

"I found confusing/mind boggling that the 'neon' lights that we see are colored by different gases, which have electrons excited with electricity, which then produces photons of different colors. The whole notion of colors caused by gases is confusing."

"How did 'radiation' become mostly known as something very dangerous? This is confusing because I feel that that word should not be so negatively looked as it seems to be most of the time."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Can we not have a quiz tomorrow?" (Don't call it a quiz--call it 'a celebration of learning.')

"I LOVE MISO SOUP. NOW I WANT SOUP. BRING MISO SOUP!!!" (Want to have some miso soup? That's your homework this weekend.)

"Astronomy is getting cooler and cooler!" (Or hotter and hotter.)

"Why are these quizzes so difficult? I can't study harder for them." (Quizzes are the toughest part of this course, but you get to drop your three lowest quizzes this semester. Also, you are expected to have nearly perfect in-class activity and online reading assignment scores, and should do much better on the midterms and the Final Exam than on the quizzes. In the meanwhile, make sure you go through the flashcard question packets and archived quizzes, and come in to office hours and/or e-mail me if you have questions.)

"Is there any extra-credit assignments we can do yet?" (Yes, but not yet. Soon.)

"Will we have a class activity that includes laying in the grass one night and finding constellations?" (Want to do some star-gazing? That's your homework this weekend. Watch out for automatic lawn sprinklers.)

20130219

Online reading assignment: magnifiers, microscopes, telescopes

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

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on magnifiers and microscopes and telescopes.

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.
"Angular magnification, because I was unaware that is was the ratio of the near point to focal length."

"Increasing the angular size increases the magnification."

"How magnifying lens don't really magnify, they just bring things into focus. I guess that makes sense when people use a magnifying glass to focus the sun."

"Images at infinity."

"How the telescope uses angular magnification to enlarge objects and the microscope as well, but with two lenses can magnify something up to 2000 times as much. I remember having a little telescope and microscope combination pen that could do both. It was a lot of fun. With the microscope piece I could look at comics in the newspaper and see the little dots that made up the color and how they mixed different dots to make different colors."

"How similar the structure of a microscope and telescope are; with just slight differences in focal lengths to change how we see through each."

"I found telescopes and microscopes interesting because they can make objects appear really close to the naked eye and because of that they have contributed to a lot of discoveries over the centuries. I learned that the objective lens creates an image, then this image becomes the object for the eyepiece."

"How there are only two lenses in a telescope--I thought that there would be more."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"The magnification process was a little confusing. I wasn't really sure if anything was being magnified."

"How is it that magnifying lenses 'don't actually magnify?'"

"The different barrel lengths and lens focal lengths for microscopes and telescopes."

"The ray tracing for a telescope seems confusing."

"Angular magnification is confusing to me. I am not sure exactly what its purpose is. I am also curious why the angles have to be in radians, when most physics is done in degrees."

"Objective and eyepiece lenses--and what happens between them is a little weird."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"When would it be a good time to go to your office, not during office hours?" (I usually stick around for 10-15 minutes after class, especially on Wednesdays. Otherwise e-mail me to arrange an appointment for times other than immediately after class, and regularly scheduled office hours.)

Online reading assignment: atmosphere problems, quantum leaps, sun's outer layers (NC campus)

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

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on problems caused by the atmosphere for telescope observing, quantum leaps, and the sun's outer layers.

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.
"Always wondered why large observatories were located in such remote locations."

"The sun, because it's something we see everyday but don't fully understand yet."

"Light pollution--you don't really take into account how many stars you can't see because of all the lights."

"Astronomers no longer study the sky by mapping constellations or charting the phases of the moon, and now the modern astronomers analyze light using sophisticated instruments and techniques to investigate the compositions, motions, internal processes, and evolution of celestial objects. This is personally interesting to see how far astronomers have come from basic understanding to a more complete understanding of what happens in the universe."

"How two or more scopes (interferometer) working together accomplish what a larger single (more expensive) telescope would do, in terms of resolving power."

"Seeing all the different types of telescopes in class. It's totally different reading about it in the textbook than actually getting to look at one in person. It helps me because I am a 100% visual learner."

"How electromagnetic waves can travel through empty space."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"The excitation of atoms. The quantum chemistry laws went over my head."

"How does turbulence in the atmosphere make the stars look like they are twinkling in the night sky?"
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Are we going to be put into groups every class?" (Yes, nearly every class you will be working in a different assigned group on an in-class activity.)

"How exactly does the diameter of a lens or mirror in a telescope determine its resolving power?" (A crude analogy would be thinking of light passing through a telescope like water coming out of a nozzle at the end of a hose--light passing through a narrower telescope lens or mirror will spread out like water passing through a narrow nozzle, losing its "directionality," which means fine details will be lost.)

"How do several telescopes work together as one (in an interferometer)? How is the light they gather combined to form one image?" (The light from each telescope is reflected through several mirrors and directed to reach the same detector simultaneously. Think of several separate mirrors that gather and reflect sunlight, and direct their beams and focusing them to the same spot (in this case, to cook something.) Now think of these several separate mirrors gathering and reflecting light from the same star during the night, directing their beams and focusing them to the same spot (in this case, a digital camera detector.))

"How do they put a telescope on a plane and make it stable? I have never been on a plane that would be stable enough for viewing space with a telescope, or even stable enough to not have to worry about my in-flight beverage spilling." (The airplane observatory flies at high altitudes when the air is clear and calm, and the telescope is also mounted such that it can be automatically stabilized independently of the airplane's motion.)

"If you can help cover the material we need to know in class it would help a lot, I've been very busy lately and haven't had much time to study." (I'm trying to "flip" the instruction in this class, where the presentations I would normally lecture during class is posted verbatim on the blog for students to read before coming to class, and to review after class. The intent is to only cover the material in class that students have trouble understanding on their own, as time allows. On occasion just a few minor concepts may need clarification in class, or sometimes the entire presentation may need to be gone over in class--so please come to class as prepared as possible so you can let me know what you need further explanation on in these online reading assignments, and I'll adapt the level and amount of instruction in each class accordingly.)

"Where can we learn to swing dance?" (The Cal Poly Swing Club (http://sloswing.com/) has beginner and intermediate lessons on Sunday afternoons during the school year.)

20130215

Presentation: charges and materials

Static electricity is never your friend. Not at the gas station. Nope. (Video link: "Fuel Pump Fire.")

In this presentation we will discuss how charges move differently through certain materials, and the effects of this behavior in certain situations.

We will assume that you already familiar with certain basics of electrostatics, in that there are positive and negative charges...

...and that two charges with opposite signs (positive-negative, or negative-positive) will attract, while two charges with the same sign (positive-positive, or negative-negative) will repel.

First, the mobility of these charges in certain materials.

We will also assume that you are already familiar with a simple atomic model of solids, where the positive charged nuclei of atoms are held at fixed locations, while their negatively charged outmost electrons are relatively free to move. The degree to which these electrons can move depends on the type of material.

For an insulator, the outermost electrons are more or less fixed to their atomic locations, but at least are able to move somewhat around these locations. (As in the gas station spark movie shown above, electrons can be exchanged when two different types of insulators that have different affinities for electrons are rubbed against each other.)

In contrast, the outermost electrons in a conductor are much more free to move about the entire material.

For a polar molecule, while the molecule itself may be neutrally charged, the electrons are distributed such that certain atoms at each end of the molecule have a permanent small positive or small negative charge. In a liquid state, these molecules would be free to align in different orientations.

Second, the response, or polarization for these different materials to external charged objects held nearby.

When a positively charged object is brought near a neutral insulator, the outermost electrons at each atom will be drawn to the side facing the positively charged object. Note that for each atom, the outermost electrons are slightly closer to the positively charged object (and feel an attractive force), while the positively charged nuclei are slightly farther away from the positively charged object (and feel a repulsive force). But since the outermost electrons are slightly closer to the positively charged object, and the positively charged nuclei are slightly farther away from the positively charged object, then the attractive forces will be slightly greater than the repulsive forces, such that there is a net attraction between the neutral insulator and positively charged object.

When a negatively charged object is brought near a neutral insulator, the outermost electrons at each atom will move to the side facing away from the negatively charged object. Note that for each atom, the outermost electrons are slightly farther way from the negatively charged object (and feel a repulsive force), while the positively charged nuclei are slightly closer to the negatively charged object (and feel a attractive force). But since the outermost electrons are farther away from the negatively charged object, and the positively charged nuclei are slightly closer to the negatively charged object, then the repulsive forces will be slightly less than the attractive forces, such that there is a net attraction between the neutral insulator and negatively charged object.

An example of this is when an insulating object (here, a cat) acquires a charge, due to rubbing or sliding against a different type of insulator. It doesn't matter whether the cat lost electrons (and thus becomes positively charged) or gained electrons (and thus becomes negatively charged) from this rubbing, as in either case the object will still attract neutral insulators (such as these styrofoam packing peanuts).

Convince yourself that a similar effect occurs when a charged object (positive or negative) is brought near a neutral conductor. While outermost electrons are much more mobile than in an insulator, they will still move to the side facing towards a positively charged object, or away from a negatively charged object, such that net attraction will result in either case.

Again, let's start with an insulating object (here, a balloon) acquiring a charge, due to rubbing or sliding against a different type of insulator (a fabric curtain). It doesn't matter whether the balloon lost electrons (and thus becomes positively charged) or gained electrons (and thus becomes negatively charged) from this rubbing, as in either case the object will still attract neutral conductors (such as this aluminum can). (Video link: "Aluminium can static roll.")

Once again a similar effect occurs when a charged object (positive or negative) is brought near a a liquid containing polar molecules. However, in this case the molecule will reorient itself such that the negative end will move to the side facing towards a positively charged object, or away from a negatively charged object, such that net attraction will result in either case.

Once again, start with an insulating object (here, a comb) acquiring a charge, due to contact with a different type of insulator (hair). It doesn't matter whether the comb lost electrons (and thus becomes positively charged) or gained electrons (and thus becomes negatively charged) from this rubbing, as in either case the comb will still attract neutral polar molecules (such as in this water stream). (Video link: "Water Bending.")

20130213

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

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

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on 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.
"I'm excited to get into more insight about telescopes! I'm also intrigued by how things don't always orbit on dead-center."

"What I knew about Galileo was a lie--Galileo did not in fact invent the telescope. But he was the one to show that Venus goes through a full set of phases--I didn't know that it did that."

"I found the illusion of a retrograding planet to be the most interesting for me once I understood it. It's crazy how planets look like they're moving backwards in the sky."

"Newton's second law--I found it especially interesting when applied to the planets. I hadn't thought about why/how the plants orbit, however, it is very interesting and logical that they are forced to orbit because of the sun's gravitational force. The last thing I expected to be the reason why planets orbit is gravitational force."

"Through Jupiter and its moons, Galileo was able to recognize that the way Jupiter could keep its moons, Earth in the same way was capable of keeping our moon. In a broader picture, the planets could be considered the sun's 'moons.'"
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Retrograde motion still confuses me."

"Reading about all the astronomers was a lot of information, and it was a little confusing, but after you map it out it starts to make sense."

"Why the planets move faster when they are near the sun."

"Reading about telescopes was not too confusing, but I would like to see how they work in class."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"You rock, P-dog! I'm really interested in this class (wish I could say that for any of my other classes)!" (I pity your other classes.)

"Can't wait to see the giant telescope in the observatory." (Me, too.)

"You should bring in Mrs. P-dog's dog." (What about my cat, with her very own Facebook page?)

"Is the rest of the class going to rely on drawing diagrams, or will it have more lecture and concept ideas? After the first quiz, it seemed as if the reading of the textbook didn't really contribute a whole lot to my level of success." (After prograde/retrograde motion, we'll be following the textbook more closely for the remainder of the semester.)

"Do you grade these online reading assignments, or is it a 'just do it' and 'get credit' sort of deal? (As long as you complete the online reading assignment in a conscientious manner (i.e., putting a serious effort in reading the textbook, previewing the presentations, and answering the questions), you'll get full credit.)

"P-dog! I'm learning a lot, and really enjoying your class! Because it is not just lectures, it's you incorporating the students into the learning." (Then it's not just what I do in class--it's what you're doing in class as well. You rock!)

"I really did not enjoy learning the history of these astronomers. Are we going to be heavily tested on that information?" (Emphasis is on what these astronomers contributed to science, whether by building or refuting models of planetary motion, and whether their contribution was based on first principles or the scientific process.)

Online reading assignment: corrective optics, magnifiers

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

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on corrective optics and magnifiers.

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 lenses can be used to correct defects in vision by determining the compensation that needs to be made to help the eye focus on the desired object; the resulting measurement is measured in diopters."

"I liked finding out what my contact prescription means!"

"I found the magnifier concept that was in the notes very interesting because the angular magnification is the ratio of angular size as when you look at a magnifier compared to the angular size of what you see with the naked eye."

"Learning about the different types of prescription lenses, because I am one of the only members in my family who doesn't wear glasses."

"I like the optical illusions of Ames room because I have been in a room sort of like this and it is a cool experience."

"Trufocals glasses are really cool! I've always thought they should make glasses like that."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Lenses in combination confuse me. I had some trouble with only one lens, and now there are several."

"I don't understand what it means when using a magnifier when it says 'the final image is formed at infinity.'"

"A virtual image from a first lens being the object for a second lens--that's just crazy."

"Four years of post-graduate optometry school were condensed into a short presentation. Why does learning optometry take so long?"

"Determining if something is enlarged or diminished."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"How can I make an appointment for office hours?" (For regularly-scheduled office hours, just show up. Otherwise e-mail me to arrange an appointment for other times during the week.)

"Can you go over the corrective optics for farsighted and nearsighted vision...do they both just form a virtual image for the eye?" (Yes, and yes.)

"Do we get to look through any optical instruments like microscopes or telescopes?" (Yes, next week in class there will be opportunities to look through compound microscopes, and refractor telescopes.)

"How does astigmatism in eyes affect vision, and how do contact lenses for astigmatism differ from typical contact lenses?" (Astigmatic eyes have different curvatures vertically versus horizontally, so eyeglasses must have different shapes vertically versus horizontally. Recently, weighted contact lenses can maintain a fixed orientation to correct for different vertical versus horizontal curvatures.)

20130212

Physics quiz question: comparing radio wave speeds

Physics 205B Quiz 1, spring semester 2013
Cuesta College, San Luis Obispo, CA

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

"Under the radio towers on Capitol Hill"
Matthew Rutledge
flic.kr/p/5JTuuF

FM radio station KCBX broadcasts at 90.1 MHz, while AM radio station KVEC broadcasts at 920 kHz[*]. Radio signals from station __________ travel with a faster speed in air.
(A) KCBX.
(B) KVEC.
(C) (There is a tie.)
(D) (Not enough information given.)

[*] radio-locator.com/cgi-bin/locate?select=city&city=San+Luis+Obispo&state=CA.

Correct answer (highlight to unhide): (C)

Wave speed v depends on the properties of the medium. Frequency f depends on the properties of the source. These two parameters can be varied independently of each other.

The wavelength λ is the parameter dependent on both of the independent parameters:

λ = v/f.

The radio waves from these two stations must have the same speed v, as they travel through the same medium. However, they can have different f frequencies (as this parameter depends only the wave source), and thus must also have different λ wavelengths (as this parameter depends on both the wave source and the properties of the medium).

Section 30882
Exam code: quiz01b3Es
(A) : 6 students
(B) : 9 students
(C) : 19 students
(D) : 1 student

Success level: 51%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.05