20150425

Astronomy quiz question: light passing through a dark nebula

Astronomy 210 Quiz 6, spring semester 2015
Cuesta College, San Luis Obispo, CA

__________ light can be seen from stars behind a dark nebula.
(A) Blue.
(B) Infrared.
(C) Ultraviolet.
(D) Doppler shifted.

Correct answer (highlight to unhide): (B)

Dust particles will scatter shorter wavelength light more than longer wavelengths. Infrared light, which is the longest wavelength light listed here, should be least affected by passing through a dark nebula.

Section 30676
Exam code: quiz06n1iI
(A) : 10 students
(B) : 20 students
(C) : 6 students
(D) : 30students

"Success level": 59% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.48

Astronomy quiz question: blue color of a reflection nebula

Astronomy 210 Quiz 6, spring semester 2015
Cuesta College, San Luis Obispo, CA

A reflection nebula appears to be blue because its dust particles:
(A) absorb red light.
(B) scatter blue light.
(C) emit blue photons.
(D) have cool temperatures.

Correct answer (highlight to unhide): (B)

Very small dust particles will scatter short-wavelength (blue) light in all directions more than scattering longer wavelengths of visible light (all other colors), such that this nebula will appear blue in color.

Section 30676
Exam code: quiz06szLR
(A) : 3 students
(B) : 37 students
(C) : 7 students
(D) : 0 students

Success level: 81% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.46

Astronomy quiz question: hydrostatic equilibrium between fusion and gravity

Astronomy 210 Quiz 6, spring semester 2015
Cuesta College, San Luis Obispo, CA

To maintain a stable size, the sun uses hydrogen fusion to counteract:
(A) gravity.
(B) dark matter.
(C) convection currents.
(D) proton-proton repulsion.

Correct answer (highlight to unhide): (A)

Hydrostatic equilibrium demands that pressure and weight must balance in order for the sun to maintain its stable size; this pressure is generated by the energy released from fusion in its core to support the weight of the outer layers of the sun produced by its gravity.

Section 30674
Exam code: quiz06n1iI
(A) : 15 students
(B) : 2 students
(C) : 10 students
(D) : 9 students

Success level: 46% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.47

Section 30676
Exam code: quiz06szLR
(A) : 27 students
(B) : 0 students
(C) : 12 students
(D) : 13 students

Success level: 61% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.69

Astronomy quiz archive: stellar evolution

Astronomy 210 Quiz 6, spring semester 2015
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz06n1iI


Section 30674
0- 8.0 :  
8.5-16.0 :   ************* [low = 11.0]
16.5-24.0 :   *********
24.5-32.0 :   *********** [mean = 21.3 +/- 7.3]
32.5-40.0 :   *** [high = 40.0]


Section 30676, version 1
Exam code: quiz06szLR


Section 30676
0- 8.0 :   * [low = 8.0]
8.5-16.0 :   ********
16.5-24.0 :   **********
24.5-32.0 :   **************** [mean = 25.2 +/- 8.2]
32.5-40.0 :   ************ [high = 40.0]

20150424

Online reading assignment: flux laws & devices

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

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

The following questions were asked on reading textbook chapters and previewing presentations on flux laws and devices.


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.
"We look at flux laws and devices here; proving them using different laws. The first law is Faraday's law which begins with the magnetic flux ΦB. The law states that the electric potential is equal to the number of coils N multiplied by the change in magnetic flux ∆ΦB over the change in time ∆t.

"I honestly do not understand any of this stuff! I know it relates to what we learned Monday and Monday's stuff made sense for the most part but I feel like this is another language! Help!"

"I understand the laws used in the presentation. Lenz's law states that direction of this induced current must 'oppose' the changes in magnetic ΦB."

"The basics of how transformers work: they take oodles of electricity and tone it down so it can actually be used."

"When there is a changing magnetic flux there is a emf. That is Faraday's law. The more coils the more emf."

"The magnetic flux ΦB is the product of the magnetic field magnitude B and the area A. The symbol '⊥' represents the maximum value for magnetic flux ΦB."

"Let's be honest. What I understand is that this stuff is confusing. I could not repeat anything back in confidence just from reading the presentation."

"When the magnetic flux is constant or unchanging the there is no induced emf in the wire loop. I understand that the amount of induced emf can be compounded by the number of coil turns N in the wire loop."

"Magnetic flux relates an area to a magnetic field. The most magnetic flux is achieved when the area is exactly perpendicular to the magnetic field lines."

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 got somewhat confused on how the primary and secondary coils gets mixed up when strength is increasing and decreasing. also, I got a little confused from how primary coil voltage can be so high and secondary too low."

"I am still kind of confused as to what a magnetic flux is exactly and how it relates to generators."

"I'm having trouble understanding when a transformer steps down voltage it actually steps up the current."

"Pretty much everything to be honest, I read the blogs and I like to tell myself that it makes it easier to see it again in class because I don't understand anything while reading."

"I need to see some simple laid-out explanations of what is expected of us in terms of formula usage and some of the basic concepts."

"So magnetic flux is sideways current? Or sideways power? I'm still trying to fully understand what a magnet is and does. Flux, coil, inducing...something? None of it makes logical sense."

"I don't really understand what magnetic flux is? Is this just magnetic force?"

"Faraday's law doesn't seem to click conceptually."

State/describe the symbol used for magnetic flux, and give its SI units.
B represents magnetic flux."

"Funny alien looking symbol."

"Wb, T·m2."

For each situation involving magnetic flux and a wire loop, determine whether or not there would be an induced current in the loop.
(Only correct responses shown.)
Constant zero magnetic flux: no induced current in loop [77%]
Constant non-zero magnetic flux: no induced current in loop. [46%]
Magnetic flux increasing in strength: induced current in loop. [82%]
Magnetic flux decreasing in strength: induced current in loop. [59%]

For an ideal transformer that "steps-down" voltage from its primary coils at 120 V to its secondary coils at 2.1 V, determine what happens to the current and to the power from its primary coils to its secondary coils.
(Only correct responses shown.)
Current: stepped-up (increases). [41%]
Power: no change. [28%]

For an ideal transformer that "steps-up" voltage from its primary coils at 1.5 V to its secondary coils at 220 V, determine what happens to the current and to the power from its primary coils to its secondary coils.
(Only correct responses shown.)
Current: stepped-down (decreases). [38%]
Power: no change. [23%]

Explain why a transformer that has the same number of primary coils and number of secondary coils would not be useful.
"The voltage stays constant."

"Because it would not transform anything, by looking at the equations we can see nothing would change. A transformer not transforming is like a heater not heating."

"There magnetic fields that are generated would be the same. So there would be no step up or down."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"The word 'flux' reminds me of the flux capacitor from the Back to the Future movies."

"Hellllppppppp."

"My mind is all fluxed up."

"Why is this class getting harder?"

20150421

Online reading assignment: the Milky Way (SLO campus)

Astronomy 210, spring semester 2015
Cuesta College, San Luis Obispo, CA

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

The following questions were asked on reading textbook chapters and previewing presentations on the Milky Way's shape, size and composition and spiral arm structure and formation.


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 can see galaxies from far away, but because of where we are, we cant see a whole lot of stars in our own galaxy. Freaky!"

"We have the capability to map out where in our galaxy our solar system is!"

"I really like being able to think that we are in a galaxy we can't see out of even though there are a multitude of them."

"Spiral arms are mostly made up of young massive stars that form and die in the arms and that's why the arms are so bright and beautiful."

"The fact that the Milky Way has a flat disk shape. I would have never pictured the shape to be like that."

"Dark matter, because the concept is intriguing and I love a good mystery."

"Where the word 'Milky Way' had originated from."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I would like some clarification on dark matter. I understand it's in the outer regions of our galaxy, but it is it something I can place in flask jar and bring back with me?"

"What density waves are, and if they cause anything else to happen."

"I don't really understand how we know about our galaxy. I got the analogy about camping but I don't understand the ways or how we deduce what our galaxy looks like."

"How we know how old our galaxy is."

"Nothing confused me."

"I don't really understand the spiral arm density waves and the PimpStar Rims. If you could go over this and the 'traffic jam' reference in class that would help."

"How they figure out the mass of the galaxy did not make sense to me."

"Where is the Milky Way? I've never seen it, or at least known which set of stars it is."

"I found it confusing how to figure out where we are in the Milky Way. This is because I couldn't understand how they could identify where we where exactly without travelling outside. Now I do understand, though."

In your experience, how much of the "Milky Way" (the band of faint stars across the celestial sphere) have you been able to see in the night sky?
As much as can be seen with the naked eye.  ************* [13]
Not very much.  *************** [15]
Barely seen it.  ********** [10]
(Never been able to see it.)  * [1]
(Unsure/guessing/lost/help!)  * [1]

Using the most powerful light-gathering telescopes in the darkest skies, up to how much of the stars in our entire galaxy can be observed from Earth?
1%.  ********* [9]
5%.  *** [3]
10%.  **************** [16]
50%.  * [1]
100%.  ** [2]
(Unsure/guessing/lost/help!)  ********* [9]

If you did not have access to a mirror while camping, what could you do to find out whether or not you're having a bad hair day?
"Use the reflection of water. Or say screw it, I don't need to impress these bears anyways."

"You could use your phone."

"Ask a friend."

"I've never had a bad hair day."

"Throw it in a bun."

"Shave my head."

"Feel your hair to find out if its messy or not."

"The shadow created by the sun."

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.
"The eye perceives a synchronized pattern as the lights move, making our eyes think we are looking at consistent image."

"There's a delay between your eyes and what your brain registers so you perceive the patterns into a single image."

"P-dog should work for Pimp My Ride and put Milky Way spinners on rims!"

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"If we take more quizzes then we have to do we get those extra points or do you just drop the lowest three scores?" (The course policy is that you keep your top five quiz scores, and drop your three lowest/missed quizzes.)
"If you could take a minute or two during class to explain how we came to believe there is a supermassive black hole at the center of the galaxy, and what that means for the death of our galaxy." (No, I will not--I know just as much as you do on that topic (i.e., I read the two pages on the supermassive black hole in the textbook), and because it's basically just factual information, it won't be on the next quiz. And no, the supermassive black hole is not going to kill us.)

"Almost two years ago there was a meteor shower and a couple friends and I drove to the middle of nowhere, where there was no light pollution, to see it. What we didn't expect was to also see the Milky Way. It was one of the most beautiful things I have every seen."

"The H-R diagram pisses me off. Makes no sense. And supernovae of all types are not explained well in the book. You should write an astronomy book, please." (No. Because writing textbooks is a trap.)

"Star Wars or Star Trek? Do not take this question lightly." (#jedihandwave This is not the answer you're looking for. But then again, there's an "epic trailer"  that might answer your question.)
"I'm going to need a little more explanation on persistence of vision and how that relates to our galaxy. P.S. Your bike is boss. No hate."

Online reading assignment: the Milky Way (NC campus)

Astronomy 210, spring semester 2015
Cuesta College, San Luis Obispo, CA

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

The following questions were asked on reading textbook chapters and previewing presentations on the Milky Way's shape, size and composition and spiral arm structure and formation.


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 enjoyed learning how astronomers determine the shape of the milky way, and theories to why the arms exist."

"The lantern analogy regarding the shape of the galaxy we're in, and how we can determine that shape by looking at the Milky Way 'strip' across the night sky."

"That dark matter exists even though we don't know what it's made of."

"I found the bad-hair day example very interesting because just the simplicity of it made sense, spiral arms equal good hair and blob equals bad hair! Although I have a buzz cut so I cant really have a bad hair day unless I spontaneously lose my hair."

"That the spiral arms of the galaxy are just an illusion they are continuously being created."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I am still confused about how and why the spiral arms continue to grow."

"I wasn't that confused with this section. My brain did have a hard time grasping the idea of dark matter."

"Radio wave maps."

"Finding the mass of the galaxy was pretty confusing, the text didn't word it very well."

"I found the PimpStar Rims confusing for two reasons:
  1. Would someone really drive around with something like that because that is just screaming to the world a bad message, and
  2. The way it works is interesting, but I can't quite grasp it, I have an idea but am uncertain."
"Where does dark matter come from and what is it?"

"How much of the Milky Way galaxy can be seen with the naked eye?"

"The spiral arms of galaxies--how they are created and how we know we have 'arms.'"

"The Milky Way kept being referred to as a disk, I'm not quite sure what that meant."

"I kind of got how to tell the distance of stars within the galaxy, but would like to get a bit more clarifying information on this."

In your experience, how much of the "Milky Way" (the band of faint stars across the celestial sphere) have you been able to see in the night sky?
As much as can be seen with the naked eye.  ************* [13]
Not very much.  ********** [10]
Barely seen it.  *** [3]
(Never been able to see it.)  ** [2]
(Unsure/guessing/lost/help!)  ** [2]

Using the most powerful light-gathering telescopes in the darkest skies, up to how much of the stars in our entire galaxy can be observed from Earth?
1%.  ***** [5]
5%.  **** [4]
10%.  ********* [9]
50%.  ******** [8]
100%.  [0]
(Unsure/guessing/lost/help!)  **** [4]

If you did not have access to a mirror while camping, what could you do to find out whether or not you're having a bad hair day?
"Have someone look at your hair for you and tell you how it is."

"Look into a still pond or a pool in a brook."

"I would grab a hair brush and french braid my hair to get it our of my face and stop bothering me."

"Eh, I would just rock it, camping is camping."

"You could look at your shadow on the ground, or feel it with your hands."

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.
"The lights cordinate when to turn on and off which when crossing our line of visions creates a pattern."

"Rapidly blinking lights can be coordinated to create patterns when swept across our field of view."

"The faster they spin the eye gets tricked and begins to see it as a still picture or light arrangement."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I always have a signal mirror with me when camping. Actually, if you want a cheap signal mirror just use an old CD. Most signal mirrors have holes in them in which you use to aim at whatever you're signalling. You can use a CD in the same manner."

"How often do you update our overall point totals (grades)?" (After each midterm, and the weekend before the final exam.)

"Where did you get your cool light thingy for your bike?" (It was a Schwinn bike accessory from Target, there are similar kits available online.)

20150420

Online reading assignment: generators

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

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

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


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.
"That some generators do not have to be reset and keep moving. These are continuous generators."

"How a generator and a motor are essentially the same thing. It all depends on whether it is receiving a rotational input on the shaft or is receiving a current flow to cause it to rotate."

"That a metal rod can become a battery when moving at constant speed. The force on the rod pumps the charge in the rod in order to maintain a constant potential difference."

"Hmmm, every lecture we are getting asked what we 'understand.' The more lectures we delve into, the less I am putting it all together and understanding."
"Still haven't gotten to it. I don't understand anything yet."

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.
"The 'hoop-drag' generator was a little difficult to visualize."

"How you would reset a single-pass generator or what constitutes as resetting."

"How continuous generators work, and how to find the forces."

"I don't quite get the point in having ac over dc, or vice versa."

"How as long as a rod moves through a magnetic field its bottom is negative and its top is positive."

"I still don't understand how to make a bicycle-powered generator to fend off the zombie hordes..."

A metal rod moves to the right along a magnetic field that points into the page. The direction of the magnetic force on (fictitious) positive charges in the rod is:
up ↑.  ********************** [22]
down ↓.  ****** [6]
left ←.  *** [3]
right →.  ***** [5]
into the page ⊗.  [0]
out of the page ⊙.  ** [2]
(No direction, as this quantity is zero.)  [0]
(Unsure/guessing/lost/help!)  **** [4]

A metal rod pivoted at one end rotates counterclockwise in a magnetic field that points out of the page. The direction of the magnetic force on (fictitious) positive charges in the rod is:
in towards the center of rotation.  ****** [6]
out away from the center of rotation  *************** [15]
into the page ⊗.  ***** [5]
out of the page ⊙.  ***** [5]
(No direction, as this quantity is zero.)  *** [3]
(Unsure/guessing/lost/help!)  ******** [8]

Explain what a generator is supposed to "generate."
"The movement of electric charges."

"emf."

"Voltage and current."

"Electrical power."

Explain the meaning of "motional" in the term "motional emf."
"It moves."

"The resulting difference in potential when moving a rod through a magnetic field."

"That the emf is created as long as the object is in motion."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"It seems that there are starting to become more than a couple lectures where this 'flipped classroom' style is not working for me. I'm reading and looking at these lectures and not much is sinking in or clicking. I guess this is just how physics goes. When you're not in love with the subject (but still quite fascinated by it) trying to comprehend how things (electricity and magnets) work is just extra-challenging. #stayfocused #onedayatatime" (At the very least your pre-reading responses let me know exactly what you are stuck on--even if it's on the basic stuff--so I know what key points to hit in the following lecture. #notallwhowanderarelost)

"Speaking of a zombie apocalypse, I am watching The Walking Dead right now and it is pretty much epic :-) Also I got a new German Shepherd today, so I am pretty sure I don't have to worry about zombies anymore."

"Still lost on concepts from this past quiz." (Let's make sure that you get caught up on this before the second midterm. See me after lecture, during office hours (make an appointment if necessary), and/or email me.)

"Can you go over the rotating metal rod? It was confusing."

"Can we go over the equations and possibly ways to remember all of them?" (Meh. The right-hand rules are probably more important.)

20150418

Physics quiz archive: circuits (2)

Physics 205B Quiz 5, spring semester 2015
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz05aL7y



Sections 30882, 30883 results
0- 6 :   * [low = 6]
7-12 :   ****
13-18 :   **********************
19-24 :   ************* [mean = 19.0 +/- 5.5]
25-30 :   ******* [high = 30]

20150417

Astronomy current events question: meteorite clues of planetary formation

Astronomy 210L, spring semester 2015
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Johnny Gibbons, "Beautiful Meteorites Hold Clues to Solar System’s Violent Start" (March 27, 2015)
http://smithsonianscience.org/2015/03/beautiful-meteorites-hold-clues-to-solar-systems-violent-start/
Analysis of __________ minerals by Smithsonian Institute researchers reveal clues about impacts that built up Earth and other terrestrial planets.
(A) meteorite.
(B) Earth's ocean floor.
(C) lunar rock.
(D) martian.
(E) fresh Earth lava.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 38 students
(B) : 7 students
(C) : 2 students
(D) : 3 students
(E) : 1 student