20140430

Online reading assignment: radioactive decay modes

Physics 205B, spring semester 2014
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 radioactive decay modes.

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"A nucleus must have just the right ratio of protons to neutrons or the atom becomes unstable."

"This presentation was an overview of basic chemistry. I never knew about the stability within the protons and neutrons."

"I understand everything in this section--it is just a lot of memorization to know what each type of process includes."

"I understand how to calculate the number of protons, electrons, and neutrons when given a variable. I get the stability conditions for atoms. I get that atoms give off radiation to become more stable."

"I remember the different types of decays from chemistry, but the presentation was a good refresher, especially about unstable and stable nuclei."

"I took a basic chemistry class last semester, so quite a bit of this stuff is fairly familiar. Also, even though I was unfamiliar with the different decay processes before this section, I feel pretty confident in my ability to utilize them when needed."

"A neutron equals a proton and an electron, and a proton equals a neutron and a positron."

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.
"Electron capture wasn't very clear on if it does anything to the protons/neutrons, I'm guessing that they stay the same. Everything else isn't too bad."

"I'm still mixing up the different kinds of decay. As in which are alpha, beta, and so forth. I think with practice I will be fine."

"Pretty straightforward. No problems so far."

Explain what a "nucleon number" is, and/or describe how to calculate it for a nucleus.
"The total number of protons and neutrons. Z + N = A."

"Denotes the number of nucleons (protons and electrons) where the number of neutrons is the nucleon number minus the atomic number."

"The nucleon number is also the 'mass number,' and it can be found in the top left corner of each elements box on the periodic table. It is the number of protons and neutron in an atom."

Identify the processes that increase, decrease, or do not change the number of protons in the nucleus.
(Only correct responses shown.)
α decay: decrease. [82%]
β– decay: increase. [75%]
β+ decay: decrease. [68%]
electron capture: decrease. [43%]
γ decay: do not change. [75%]

Identify the processes that increase, decrease, or do not change the number of neutrons in the nucleus.
(Only correct responses shown.)
α decay: decrease. [50%]
β– decay: decrease. [79%]
β+ decay: increase. [71%]
electron capture: increase. [32%]
γ decay: do not change. [79%]

Identify the processes that change a proton to a neutron, or change a neutron to a proton in the nucleus.
(Only correct responses shown.)
α decay: no p/n conversion. [61%]
β– decay: n → p. [79%]
β+ decay: p → n. [79%]
electron capture: p → n. [36%]
γ decay: no p/n conversion. [82%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Can we make antimatter?" (Ask your doctor if you can get a PET scan. They'll typically inject you with fludeoxyglucose containing 18F atoms, which will undergo β+ decay. Since the β+ particle is a positron--the antimatter version of an electron--you will be "making" antimatter.)

"I wish there was more math and equations instead of just stuff to memorize."

"I just want to go over examples of each decay process and then I'll be good."

"A lot of late second-semester chemistry carryover."

"This material is really interesting. I am looking forward to this lecture"

20140428

Online reading assignment: radioactive decay rates

Physics 205B, spring semester 2014
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 radioactive decay rates.

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"I do vaguely remember the radioactive decay equation from pre-calculus. I get that the more atoms there are the older the object being tested."

"Radioactive atoms decay into daughter atoms. In one half-life, half of the radioactive atoms in a sample decay into their daughter atoms."

"You can reset the solidification age of a radioactive material if you melt it. This means it will have no daughter atoms when it resolidifies."

I liked the M&M's™ example. It really showed me how much probability plays into decay."

"I understand the average lifetime before decay and the half life and how they relate to one another."

"Didn't get much done over break."

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.
"Nothing."

"The toy model of a radioactive substance was a little confusing. Also I couldn't really wrap my mind around a time constant and how it could be equal to approximately the average lifetime of a single M&M™ before it decays."

"The equations will confuse me as soon as I try to use them."

"Why are the equations so different than from an exponential decay problem from calculus?"

"I don't know why the M&M's™ don't have a 0.50 half-life."

"It seems confusing to find the radioactive age of a substance. I understand the explanation but I would benefit from practice."

State the SI units for activity (radioactive decays per time).
"Probability/ second."

"Lambda."

"SI unit for activity is the becquerel. 1 becquerel (abbreviated 'Bq') is 1 disintegration per second."

Explain what the Greek letter τ ("tau") refers to when used in radioactive decay calculations.
"Tau is the time constant, which is 1/λ. It is the average time that a nucleus survives before decaying."

What is the mathematical relationship between τ and half-life for radioactive decays?
"They are inverses of each other."

"T1/2 = τ·ln(2)."

"I'm not sure. I'm confused on this."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I'm radioactive, radioactive." (Is this what you kids listen to these days? Or did you mean this video?)

"Yes...M&M's™. Nom nom nom."

"What did you do for spring break?" (I managed to both impress Mrs. P-dog and avoid killing myself...USING PHYSICS.)

"I think after I see some sample problems I will be okay with this section."

"What is decay referring to? When a nucleus decomposes and splits?" (That sounds like fission. A decay is just a conversion of a nucleus to a slightly more stable form, usually by converting or ejecting protons and/or neutrons, as we'll see in the next class.)

20140425

Physics quiz question: replacing light bulb with ideal wire in parallel branch

Physics 205B Quiz 5, spring semester 2014
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Questions 18.21-18.23.

An ideal 6.0 V emf source is connected to an ideal ammeter, a light bulb, and two resistors, as shown at right. The ammeter reading if the light bulb were instead replaced with an ideal wire would be __________ the ammeter reading while the light bulb was lit.
(A) less than.
(B) equal to.
(C) greater than.
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (B)

From applying Kirchhoff's loop rule for circuits to the outermost loop (shown in green), the amount of current flowing through the ammeter will be unaffected by changes in the other parallel (uncolored) branch. Thus the ammeter reading will be the same whether the light bulb is replaced with wire, or is left intact.

Sections 30882, 30883
Exam code: quiz05b4L8
(A) : 15 students
(B) : 14 students
(C) : 9 students
(D) : 0 students

Success level: 37%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.52

Physics quiz question: brighter light bulb?

Physics 205B Quiz 5, spring semester 2014
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Questions 18.21-18.23

An ideal voltmeter is connected to a switch in a circuit with an ideal 12.0 V emf source and two light bulbs, as shown at right. While the switch remains open, the __________ light bulb is brighter.
(A) 3.0 Ω.
(B) 5.0 Ω.
(C) (There is a tie.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (B)

No current will flow through the ideal voltmeter and its connecting wires (shown in blue), only through the lower part of the circuit (indicated in green). Since the 3.0 Ω and the 5.0 Ω light bulbs are in series, from applying Kirchhoff's junction rule for circuits both light bulbs must have the same amount of current passing through them. As brightness is related to power dissipated, which depends on current, voltage drop, and resistance:

P = I·∆V = I·(I·R) = I2·R,

then with the same amount of current passing through each light bulb, the greater resistance 5.0 Ω light bulb will dissipate more power, and be brighter than the 3.0 Ω light bulb.

Sections 30882, 30883
Exam code: quiz05b4L8
(A) : 12 students
(B) : 17 students
(C) : 9 students
(D) : 0 students

Success level: 45%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.38

Physics quiz question: voltmeter reading of "open switch"

Physics 205B Quiz 5, spring semester 2014
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 18.73

An ideal voltmeter is connected to a switch in a circuit with an ideal 12.0 V emf source and two light bulbs, as shown at right. While the switch remains open, the voltmeter reading is:
(A) 0 V.
(B) 4.5 V.
(C) 7.5 V.
(D) 12.0 V.
(E) ∞.

Correct answer (highlight to unhide): (C)

No current will flow through the ideal voltmeter, only through the lower part of the circuit (indicated in green). Since the 3.0 Ω and the 5.0 Ω light bulbs are in series, the equivalent resistance of the circuit is their arithmetic sum, Req = 8.0 Ω. This means that the current in this circuit is:

Icircuit = εeq/Req = (12.0 V)/(8.0 Ω) = 1.5 A.

The voltmeter will "feel" the total difference in potential of the emf and the 3.0 Ω light bulb together (where its connection to the circuit is shown in blue). The emf and the 3.0 Ω light bulb contribute a voltage rise of ε and a voltage drop of I·R, respectively:

V = +ε – I·R = +(12.0 V) – (1.5 A)·(3.0 Ω) = +12.0 V – 4.5 V = +7.5 V.

(Alternatively, as wired the voltmeter also "feels" just the voltage drop of the 5.0 Ω light bulb, which would be ∆V = – I·R = –(1.5 A)·(5.0 Ω) = 7.5 Ω. This would be expected from applying Kirchhoff's loop rule for circuits. Note that as in the laboratory component of this course, the affect of the polarity (and thus the ± sign of voltmeter readings) of wiring the voltmeter to a circuit is neglected.)

Sections 30882, 30883
Exam code: quiz05b4L8
(A) : 18 students
(B) : 1 student
(C) : 6 students
(D) : 10 students
(E) : 3 students

Success level: 16%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33

Astronomy quiz question: comparing star cluster ages

Astronomy 210 Quiz 6, spring semester 2014
Cuesta College, San Luis Obispo, CA

A star cluster containing white dwarfs would be __________ a star cluster containing massive protostars.
(A) younger than.
(B) the same age as.
(C) older than.
(D) (At least one of these star clusters cannot exist.)

Correct answer (highlight to unhide): (C)

All stars in a star cluster are born at the same time, but undergo stellar evolution at different rates depending on their masses. Medium-mass stars evolve slower than massive stars, so a star cluster containing medium-mass stars that already have reached the end of the main-sequence lifetimes to reach their white dwarf end-stage must be much older than a star cluster containing massive protostars that have not yet begun their main-sequence stage.

Section 30674
Exam code: quiz06n0mM
(A) : 8 students
(B) : 1 student
(C) : 16 students
(D) : 0 students

Success level: 66% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.27

Section 30676
Exam code: quiz06sn0V
(A) : 8 students
(B) : 1 student
(C) : 31 students
(D) : 1 student

Success level: 77% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.36

Astronomy quiz question: compact object with accretion disk

Astronomy 210 Quiz 6, spring semester 2014
Cuesta College, San Luis Obispo, CA

A __________ with a companion star can have a glowing x-ray accretion disk.
(A) white dwarf.
(B) neutron star.
(C) black hole.
(D) (Two of the above choices.)
(E) (All of the above choices.)
(F) (None of the above choices.)

Correct answer (highlight to unhide): (E)

Depending on the initial mass of the compact object--whether a very massive star, a massive star, or just a slightly more massive medium-mass star--this compact object could be a black hole, neutron star, or white dwarf. In all these cases, the compact object would have completed its stellar evolution faster than and be sufficiently close enough to its companion star (that would have been a medium-mass star that has just finished its main-sequence lifetime to become a giant) to accumulate hydrogen from its expanding outer layers.

This infalling hydrogen collects into an accretion disk surrounding the companion star, and due to Kepler's third law, the outer part of the disk orbits slower than the inner part of the disk. Due to the density of the disk, the difference in speeds between adjacent parts causes friction, producing enough heat for the disk to become incandescent, thus emitting blackbody radiation that peaks in the x-ray portion of the electromagnetic spectrum.

Section 30674
Exam code: quiz06n0mM
(A) : 3 students
(B) : 8 students
(C) : 6 students
(D) : 4 students
(E) : 4 students
(F) : 0 students

Success level: 21% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.27

Astronomy quiz question: white dwarf accretion companion

Astronomy 210 Quiz 6, spring semester 2014
Cuesta College, San Luis Obispo, CA

A white dwarf with a __________ companion can have a glowing x-ray accretion disk.
(A) protostar.
(B) black hole.
(C) neutron star.
(D) giant.

Correct answer (highlight to unhide): (D)

The accretion disk around a white dwarf is made of hydrogen accumulated from a companion. This would eliminate neutron stars and black holes, as they do not have any hydrogen remaining. A protostar and a giant would both be made of hydrogen (in the case of giants, in their outer layers), but a companion close enough to transfer material would need to have been born at the same time as the white dwarf. This makes it very unlikely that the companion star would be a low-mass protostar that has not even started its main-sequence lifetime, yet close enough to transfer hydrogen to the white dwarf. It would be much more likely that the companion star would have been a slightly less massive medium-mass star that has already gone through its main-sequence lifetime, and as a giant expanded its outer layers enough such that the white dwarf (which started as a slightly more massive medium-mass star) can begin accretion.

(This infalling hydrogen collects into an accretion disk surrounding the white dwarf, and due to Kepler's third law, the outer part of the disk orbits slower than the inner part of the disk. Due to the density of the disk, the difference in speeds between adjacent parts causes friction, producing enough heat for the disk to become incandescent, thus emitting blackbody radiation that peaks in the x-ray portion of the electromagnetic spectrum.)

Section 30676
Exam code: quiz06sn0V
(A) : 11 students
(B) : 2 students
(C) : 16 students
(D) : 12 students

Success level: 32% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.73

20140418

Astronomy current events question: BICEP2 evidence of cosmic inflation

Astronomy 210L, spring semester 2014
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!)
Cynthia Eller, "BICEP2 Discovers First Direct Evidence of Inflation and Primordial Gravitational Waves," March 17, 2014
http://www.caltech.edu/content/bicep2-discovers-first-direct-evidence-inflation-and-primordial-gravitational-waves
Jon Kaufman and Jorge Cham, "PHD Comics: Cosmic Inflation Explained," March 19, 2014
http://www.phdcomics.com/comics.php?f=1691
The BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) telescope in Antarctica observed fluctuations in the cosmic microwave background caused by:
(A) inflation just after the Big Bang.
(B) wormholes.
(C) matter-antimatter annihilation.
(D) the first generation of stars.
(E) galaxies moving away from each other.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 31 students
(B) : 1 student
(C) : 2 students
(D) : 3 students
(E) : 7 students

Astronomy current events question: Dark Energy Camera dwarf planet discoveries

Astronomy 210L, spring semester 2014
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!)
Aviva Rutkin, "Gaggle of Dwarf Planets Found by Dark Energy Camera," April 2, 2014
http://www.newscientist.com/article/dn25351-gaggle-of-dwarf-planets-found-by-dark-energy-camera.html
Researchers using the Dark Energy Camera in Chile discovered __________ in the outer reaches of the solar system.
(A) several dwarf planets.
(B) spacetime fluctuations.
(C) a companion red dwarf.
(D) a new asteroid belt.
(E) dark matter pockets.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680
(A) : 36 students
(B) : 2 students
(C) : 1 student
(D) : 0 students
(E) : 5 students

Astronomy current events question: detecting Enceladus' underground ocean

Astronomy 210L, spring semester 2014
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!)
Dwayne Brown, Jane Platt, and Brian Bell, "NASA Space Assets Detect Ocean inside Saturn Moon," April 3, 2014
http://www.nasa.gov/press/2014/april/nasa-space-assets-detect-ocean-inside-saturn-moon/
NASA's Deep Space Network observed the Cassini spacecraft __________ to determine that Saturn's moon, Enceladus, has a large underground ocean.
(A) fluctuating in temperature.
(B) passing behind water vapor geysers.
(C) deviating from its flight path.
(D) covered by icy particles.
(E) reflecting laser beams.

Correct answer: (C)

Student responses
Sections 30678, 30679, 30680
(A) : 6 students
(B) : 18 students
(C) : 15 students
(D) : 3 students
(E) : 2 students

20140417

Astronomy quiz archive: stellar evolution

Astronomy 210 Quiz 6, spring semester 2014
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz06n0mM


Section 30674
0- 8.0 :
8.5-16.0 : **** [low = 12.0]
16.5-24.0 : ********* [mean = 23.3 +/- 6.9]
24.5-32.0 : **********
32.5-40.0 : ** [high = 40.0]


Section 30676, version 1
Exam code: quiz06sn0V


Section 30676
0- 8.0 : * [low = 4.0]
8.5-16.0 : **
16.5-24.0 : *****************
24.5-32.0 : *********** [mean = 25.7 +/- 8.2]
32.5-40.0 : ********** [high = 40.0]

20140416

Online reading assignment: the Milky Way (SLO campus)

Astronomy 210, spring semester 2014
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 found how we are able to accurately describe how to the Milky Way is shaped is pretty interesting seeing as how we are in it."

"I think dark matter is interesting. the fact that something has such a strong gravitational force but we can't see it."

"I thought that the fact that the birth of stars is triggered by density waves and then lead to the type II supernovae explosions that are just plain epic and hard to fathom for a human mind. Also the idea that they must continuously swallow nearby dwarf galaxies for it all to occur is just a trip! Perpetuation of life in cycles is just really interesting to me for some reason."

"I love the Milky Way! I still remember learning about it way back when I was in 1st grade! It's so beautiful when you look up in the night sky and see it, its magic! I think its interesting learning about it after admiring it for so many years."

"I always thought Nibbler's poop was what dark matter was, now my mind is blown haha."

"I thought it was interesting that the Milky Way was named because the greeks thought it was a milky river flowing through the night sky. I thought a similar thing when I was little."

"I think that the persistence of vision concept is pretty interesting. I've never really seen anything like that before."

"Something that was interesting was the fog model, this was interesting because I liked the visual aid."

"I found it really interesting that in the Milky Way's spiral arms, massive stars are born and die at certain times as they orbit which helps to create the illusion."

"Dark matter, it makes a great source of evil since it is an unknown form of matter. Its also crazy that it is still a fundamental problem of modern astronomy."

"Your 'P-dog' lights on your bike! That made me laugh so hard! 'They see me rollin...' Too funny!"

"I thought that the traffic jam example was really interesting. A lot of your 'real world' applications help things click for me."

"I found the MonkeyLectric rims really awesome! I would like to get some for my mom's bike to keep her safe (and look really awesome) when she is riding at night!"

"It was interesting to learn that the sun and our solar system are located near the edge of the disk of the Milky Way. I guess us Earthlings are pretty self-centered, since I've always just assumed we would be located in the central bulge."

"I didn't know our galaxy was so exceptional structurally or aesthetically."

"I had to look YMMV up on UrbanDictionary.com. I feel un-hip."

"I thought it was very interesting learning about the spiral arms. How they learn about them is locating the O-type and B-type stars, which are often found because they are really luminous and also easy to detect from great distance. I also found it interesting how the spiral arms are where star formation happens."

"I found that the spiral arm formation of the Milky Way was very interesting, and how they are being 'cut off' and are regrowing. I liked this comparison because I love starfish and it will be easy to remember."

"I thought it was interesting how we were able to determine that our galaxy has a disk shape."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"This is all very confusing to me, I'm not really understanding how the whole illusion called persistence of vision works. Or what this has to do with the Milky Way and stars, please more explanation needed."

"How is the spinning of the Milky Way relayed to the way light-up rims spin on cars?"

"I don't understand how globular clusters tell help us determine the shape of our galaxy."

"I've been gone for awhile so pretty much everything."

"I found the spiral density wave theory confusing. I am not completely sure how star formation occurs by gas clouds passing through spiral arms."

"I didn't find anything confusing."

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.  ******************* [19]
Not very much.  ************ 12]
Barely seen it.  **** [4]
(Never been able to see it.)  *** [3]
(Unsure/guessing/lost/help!)  [0]

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%.  ************ [12]
5%.  *** [3]
10%.  ************** [14]
50%.  *** [3]
100%.  ** [2]
(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?
"Find a still puddle of water."

"A spoon!"

"Ask a friendly squirrel! If it scurries away in horror, I'll know the answer..."

"To be honest I don't care, when I go camping I don't really care what I look like."

"I have the curliest hair ever. Every day is a bad hair day."

"Since no one goes camping alone (or should), just ask whoever you're with."

"Well, I don't brush my hair on a daily basis, so I'm always having a bad hair day."

"I'm never having a bad hair day. I have a shaved head, bro."

"If I really had some ridiculous reason to be worried about such issue, I would look in the lens mirror reflection of a friend's sunglasses."

"This question is irrelevant. My hair is always on point."

"Take a #selfie. Delete it if you're having a bad hair day, save it if it's a good hair day."

"I would look at the screen on my phone."

"I would feel around with my hands, I guess--honestly I like my hair messy."

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.
"Both consist of lightbulbs that flash and when put in motion create a patter or seemingly solid color. It like a fan, when the fan is not turned on you can see the propellers but once its in motion they all become a blur. Same with the lights on either car rims or bike wheels, the lights blur together due to the wheel's motion creating either a word or blurred effect (solid color, blue as in the example image)."

"The blinking lights can be timed to the speed of the wheel to light up at the right time to produce a pattern on the wheel."

"I'm not sure at all...through a computer?"

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Did you get to see the lunar eclipse on Monday?" (Yes, but I almost missed seeing it. True story, bro.)

"Here's a really cool stabilized *.gif of the lunar eclipse from last night I found online." (Awesome.)

"When is our final and what time is it?" (Wednesday, May 21, 4:30-6:30 PM in this room. It's also marked on the course calendar.)

"How did you swoon Mrs. P-dog?" (With my swing dancing skills.)

"Is Quiz 8 really just 40 freebie points? If so, I'd like to give you a hug." (Well, you would just need to complete the education-research questionnaires during the last week of class. And psychic hugs only, please. PSYCHIC HUGS.)

Livetweets: April 14-15, 2014 total lunar eclipse

Online reading assignment: flux laws & devices

Physics 205B, spring semester 2014
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.
"The SI units are starting to stick."

"Dang. This is going to be a difficult section."

"I understand that the area enclosed by a rod-rail circuit that the magnetic field lines passes through increases, and therefore the magnetic flux increases and this area increases. That is why there is no magnetic flux if the rod is stationary. I can also apply this concept of increasing area to a rotating-coil generator."

"Lenz's law is responsible for the negative sign in Faraday's law, and this negative sign has an important meaning. There are going to be two possibilities for the direction of a current induced in a wire loop, due to the changes in magnetic flux ΦB through it. Lenz's law states that direction of this induced current must "oppose" the changes in magnetic ΦB."

"Faraday's law is a statement that an induced emf ε occurs in a wire loop while the magnetic flux ΦB through it changes, whether the magnetic field gets stronger or weaker, or by changing the orientation of the surface such that more or fewer magnetic field lines go 'through' the surface."

"Transformers: voltage increase causes a current decrease and vice versa. The magnetic field lines and a wire circle hate change and in order to keep the status quo the current in the wire will change accordingly."

"I understand that so long as the magnetic field is perpendicular to the surface area, the magnetic flux will have a maximum value. If on the other hand, the magnetic field is parallel to the surface area then the magnetic flux will equal zero."

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 am a little confused on the idea of a rotating-coil generator. It seems a little strange to me that the faster the coil rotates the more current and induced emf is produced. Is there a maximum that it will go or is it going to keep going forever?"

"Where do I start? How about....everything. Can we please go over this extensively in class?"

"I find most of the rest of the material confusing. I don't understand Faraday's law, Lenz's law, or transformers very well :/ I am going to need to pay really close attention in lecture tomorrow."

"I still don't understand the concept of flux very well. I understand the units, but is it only present in a moving system or can the area and field be stationary?"

"How does the coil 'know' the direction that the induced current must flow in order to resist changes in the external magnetic field? I don't get it or understand."

"It was a little hard to grasp how the induced current opposes the magnetic flux change."

State/describe the symbol used for magnetic flux, and give its SI units.
B is the product of a magnetic field B and an area A and its units are webers (Wb) or teslas·m2."

"Phi, webers or volt-seconds."

"Tesla's symbol is B."

For each situation involving magnetic flux and a wire loop, determine whether or not there would be an induced current in the loop.

If the magnetic flux through the loop is __________, this would __________ a current in the loop.

(Only correct responses shown.)
zero: not induce. [81%]
increasing in strength: induce. [81%]
decreasing in strength: induce. [70%]
a constant value: not induce. [56%]

Briefly describe what a transformer is supposed to "transform."
"A transformer allows voltage to either be stepped down or stepped up."

"Transformers alter the magnetic field of the secondary coil, inducing a greater or lesser emf into the circuit."

"A transformer uses what's known as 'induction' to change voltage. Transformers don't create energy, the overall amount of power remains the same."

"It transforms power."

Identify the conserved (or non-conserved) quantities that are put into the first coil, and output from the second coil of an ideal transformer.
(Only correct responses shown.)
Voltage: not conserved. [56%]
Current: not conserved. [44%]
Power: conserved. [61%]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"If you don't change the flux is there a way to still induce an emf? (No.)

"So how did the aluminum plate levitate?" (A coil below changes the magnetic flux through the plate, which induces current in the plate. The induced current in the plate moves in the direction such that the magnetic field of the current pushes up on it. We can work out the Lenz's law and right-hand rules on this in class as time allows.)

"How can you tell when to use I instead of v for the thumb during RHR1?" (Use your right thumb for v for the direction of positive charges. Since current I is defined to be the flow of positive charges, then you can also use your right thumb for the direction of current as well.)

20140415

Online reading assignment: the Milky Way (NC campus)

Astronomy 210, spring semester 2014
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 found it very interesting that we can deduce what type of galaxy we are just using the naked human eye. Personally, I'm continually impressed by the sheer observational power of humans, and the intelligence required to think about something as large as a galaxy."

"The spiral arms because it is constantly changing and almost like a circle of life but for stars."

"The beautiful shape of our galaxy. It's interesting because it is elegantly pretty."

"The formation of the spiral spurs was interesting to be because I think it's fascinating how they are self-sustaining."

"The fact that the Milky Way contains billions of stars and planets and it's just a tiny part of the entire universe. Not sure if amazing or terrifying."

"I found spiral arms interesting because one from our own galaxy can be seen on a clear night. It gives me the sense of how small I really am in the grand scheme of things."

"Learning about them cool spiral galaxies."

"I thought that the part about the spiral arms of galaxies was really interesting. I thought it was interesting how some have more spirals than others. All the forms it can take are really cool and beautiful."

How our galaxy absorbs dwarf galaxies is pretty cool."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Dark matter. Definitely going to need some explaining on this one. What I am most confused about is the two types of possible dark matters, MACHOS and WIMPS, and how dark matter could be so dense that it would move the galaxy. Mind blowing..."

"That we don't really know what dark matter is."

"Dark matter. It is confusing because we know something is creating a lot of gravity in the galaxy, but we are unsure exactly what it is--called 'dark matter.'"

"The gas and dust compression [for new star formation in the spiral arms] is a little confusing. Why does it happen at particular times?"

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.  ******** [8]
Not very much.  ******* [7]
Barely seen it.  ** [2]
(Never been able to see it.)  ** [2]
(Unsure/guessing/lost/help!)  [0]

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%.  **** [4]
5%.  * [1]
10%.  ******* [7]
50%.  ** [2]
100%.  [0]
(Unsure/guessing/lost/help!)  ***** [5]

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?
"I would use the reflection of my sunglasses."

"I would suggest trying to find water first so you can see somewhat of your reflection but if there is no water you can feel your hair with your hands and then you can tell what shape it is and if its unruly or not."

"A spoon."

"Well, first off, I am camping, it doesn't matter what my hair looks like! BUT, if I did worry about it, I would take a 'selfie' if I had my phone, or look in a river, lake or stream. If I was camping and had my car around, I would use a mirror. But I reiterate, I am camping--what my hair looks like, or how my breath smells--doesn't matter! HA!"

"I would find the nearest bear and ask if it had a mirror I could borrow briefly."

"Being the turbo nerd that I am, I usually bring my laptop with me everywhere--I'd just turn on the webcam and use that to tidy myself up."

"Dunk your head in water and you don't have to deal with the problem again until it dries. Or you could ask someone, but people lie to make you feel good. You may never really know."

"We're are but tiny ants in this humongous galaxy, does it really matter what our hair looks like one day out in the wilderness? Yes--you don't want people mistaking you for an animal that lives in the forest."

Look at PimpStar Rims (*.html) for cars, or MonkeyLectric Rims (*.html) for bikes. Briefly explain how they work.
"LEDS in the rim light up, and I would imagine the created image would have to rotate equally to the speed of the tire spin... $12,000 is a lot of money for pimpin' rims."

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

"The PimpStar Rims or MonkeyLectric Rims are visual illusions. Some lights blink shortly or are on for a brief period of time and while in motion, there is a pattern."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Do you have pimp wheels?" (Yes, on my bicycle. So if you see me rolling at night, don't be hating.)

"I've seen a good portion of the Milky Way a couple of nights. It's pretty cool."

"This might be a really stupid question, but where does the stuff that goes into a black hole go?" (Well, from an outside observer's viewpoint, that stuff just circles closer and closer inwards without actually getting "into" the black hole. From the viewpoint of your spaghettified atoms, they just fall "onto" the point-like singularity in a finite amount of time, and become part of its mass...thereby making the black hole gravitationally stronger!)

20140414

Online reading assignment: generators

Physics 205B, spring semester 2014
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.
"There two types of generators that produce current and motional emf. One type of generators ('single-pass') needs to be reset after it has been through the passageway, and 'continuous' generators do not need to be reset as it turns around and around as it creates current and motional emf."

"You can make a battery by encouraging electrons to collect at one end of a device and leaving the other end electronless. This can be done by passing the device over a magnetic field, rotating the disk-shaped device around a magnet or rotating the coil-shaped device around a magnet."

"A ingle pass generator creates a 'motional' emf by moving a rod through a magnetic field. If this rod is touching two rails, it can take advantage of this emf. Of course, this would at some point need to be reset. Continuous generators also create a "motional" emf...keep cranking."

"Liking this section! Very much enjoyed the 'Faraday disk' and 'rotating coil' examples because, for once, I can kind of see conceptually how a generator (at a very basic level, I'm sure) works."

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.
"What was harder for me to understand was a continuous generator. Why doesn't it have to restart in order to provide current?"

"I have a very basic understanding of generators. It seems the different approaches are different set ups for the same concept, which makes sense, but some clarification would be nice."

I'm kind of stuck on left and right hand rules."

"Not sure how to visualize a hoop drag generator."

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 ↑.  ************ [12]
Down ↓.  ****************** [18]
Left ←.  *** [3]
Right →.  ** [2]
Into the page ⊗.  * [1]
Out of the page ⊙.  * [1]
(No direction, as the magnetic field is zero.)  [0]
(Unsure/guessing/lost/help!)  [0]

Explain what a generator is supposed to "generate."
"Electricity from mechanical energy."

"Voltage."

"An emf?"

"An emf without the use of a battery or outside source of electricity."

"A motional emf that produces a current."

Explain the meaning of "motional" in the term "motional emf."
"Motional means moving or mobile system that creates current."

"A motional emf is produced by moving (this is the motional part) an object through a magnetic field."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Is it possible to connect one generator up to another in a reversed fashion so that the magnetic force of one will drive the turbine of the other and vice versa?" (Yes.)

"If you need power to rotate the devices or pass the device through the magnetic field in order to make the battery, doesn't that kind of defeat the purpose? There must be a lot more power we're getting than what we're spending...or maybe this is just a 'cool' way of generating power, but it's not really practical?" (If you have access to motional energy that is already there--such as the wind, or water--then you can use that to run a generator to convert this motional energy into electricity.)

"For the bicycle generator, would it be an ac generator with a split-ring commutator and brushes to make the emf go in one direction like a dc generator?" (Since an incandescent light bulb would work with either ac or dc current, it's hard to tell.)

20140411

Astronomy current events question: space telescope "starshade"

Astronomy 210L, spring semester 2014
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Whitney Clavin, "Space Sunflower May Help Snap Pictures of Planets," March 20, 2014
http://www.jpl.nasa.gov/news/news.php?release=2014-089
NASA engineers proposed a space-based telescope with a flower-shaped "starshade" to:
(A) detect exoplanets around stars.
(B) propel it out of the solar system.
(C) help keep the telescope cool.
(D) protect it from micrometeorites.
(E) collect interstellar dust particles.

Correct answer: (A)

Student responses
Sections 30678, 30679, 30680, 30682
(A) : 40 students
(B) : 5 students
(C) : 5 students
(D) : 7 students
(E) : 5 students

Astronomy current events question: finding particles collected by NASA Stardust

Astronomy 210L, spring semester 2014
Cuesta College, San Luis Obispo, CA

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Richard A. Kerr, "Spacecraft Returns Seven Particles From Birth of the Solar System," March 21, 2014
http://news.sciencemag.org/space/2014/03/spacecraft-returns-seven-particles-birth-solar-system
Interstellar dust particles in NASA's Stardust aerogel collector were located by:
(A) trained service dogs.
(B) "crowdsource" volunteers.
(C) automatic computer algorithms.
(D) washing down the spacecraft.
(E) radioactivity levels.

Correct answer: (B)

Student responses
Sections 30678, 30679, 30680, 30682
(A) : 1 student
(B) : 39 students
(C) : 10 students
(D) : 7 students
(E) : 6 students

Astronomy current events question: asteroid Chariklo rings

Astronomy 210L, spring semester 2014
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!)
Felipe Braga-Ribas, Bruno Sicardy, José Luis Ortiz, and Richard Hook, "First Ring System Around Asteroid," March 26, 2014
http://www.eso.org/public/news/eso1410/
The rings around asteroid Chariklo were discovered by telescopes observing:
(A) from different angles.
(B) multiple collisions.
(C) infrared emission from dust.
(D) blocked starlight.
(E) reflected sunlight.

Correct answer: (D)

Student responses
Sections 30678, 30679, 30680, 30682
(A) : 7 students
(B) : 3 students
(C) : 12 students
(D) : 35 students
(E) : 5 students

20140410

Physics quiz archive: circuits (2)

Physics 205B Quiz 5, spring semester 2014
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz05b4L8



Sections 30882, 30883 results
0- 6 :   **** [low = 3]
7-12 :   **********
13-18 :   ********* [mean = 17.0 +/- 6.7]
19-24 :   ***********
25-30 :   **** [high = 30]

20140409

Online reading assignment: magnetic fields of current-carrying wires and loops

Physics 205B, spring semester 2014
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 re-reading textbook chapters and reviewing presentations on magnetic fields of current-carrying wires and loops.

Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"I understand that the second right hand rule should be used for a straight section of current carrying wire and the third right hand rule should be used for a circular loop of current carrying wire. The magnetic field for the second right hand rule will be in the direction of the curled fingers whereas in the third rule, the thumb will point in the direction of the magnetic field."

"It's cool how the iron fillings in oil line up parallel to the magnetic field around them."

"I get the concept of the magnetic field model where the source object creates a magnetic field and it exerts a force on a test object (a lot of similar concepts from the electric field model)."

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.
"Pretty much all of it."

"I'm thinking that remembering which fingers go where in a specific situation will be the toughest thing for me at this point. Of course, nothing serves as a better remedy as habitual and continued practice, so I should get the hang of this soon."

"Nothing yet."

"I could use some further explanations on source objects and the differences and similarities between straight wires and loops."

"I found the idea of solenoids to be confusing. I understand how they are very similar to circular current loops but I don't really understand this concept."

State/describe the symbol used for the "permeability of free space," and give its SI units.
"The symbol is a weird Latin-ish looking lowercase 'u' (the same letter used as the prefix for 'micro' in unit conversions) followed with a '0' in subscript. It's units are in T·m/A."

"Unsure what this is."

0, henries per meter."

"'mew,' newtons per ampere squared."

For the magnetic field created by current in a long straight wire, indicate which right-hand finger(s) point along which directions.
(Only correct responses shown.)
Current I in long straight wire: thumb [97%]
Magnetic field B: curled fingers [97%]

For the magnetic field created by a current in a circular loop of wire, indicate which right-hand finger(s) point along which directions.
(Only correct responses shown.)
Current I in circular loop of wire wire: curled fingers [83%]
Magnetic field B: thumb [83%]

Explain the similarities/differences between a circular current loop, and a solenoid.
"Solenoid has a longer length compared to its diameter. The Distance between two loops in a solenoid is longer."

"I'm not really grasping what a solenoid is."

"Both have looping field lines that pass through the middle and then loop back outside and around to complete their circuit. A solenoid is a helix of loops such that the field lines in the middle of the helix are near parallel."

"A solenoid has a large number of circular current loops. The field lines emerge from one side of the current look and solenoid and reenter the other side for both."

"The 'solenoid' is from Greek word for 'channel.' It is temporary strong magnet, when connected through external source like battery or when electricity passed through it. It is also known as an electromagnet."

"I'm lost."

"VFPt_Solenoid_correct2.svg"
http://en.wikipedia.org/wiki/File:VFPt_Solenoid_correct2.svg
Geek3

Determine which solenoid end (*.html) corresponds with which magnetic pole.
(Only correct responses shown.)
Left end: south pole [69%]
Right end: north pole [69%]

Briefly explain your reasoning for choosing which solenoid end corresponds with which magnetic pole.
"Confused!"

"The magnetic field lines exit out the right end and return via the left."

"In seeing the direction of the magnetic field lines they go on the outside from right to left in a N/S bar magnet the lines go from the north end to the south on the outside."

"The field by the solenoid is similar to that of a short bar magnet."

The B field comes out of the north pole and into the south pole."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"What is flux?" (You mean, 'what the flux?' More seriously, we'll cover this next week.)

"How safe are electromagnets? Well, a home-made electromagnets? I kind of made one by accident a year ago." (They shouldn't be dangerous, as long as you keep them away from magnetic media (credit cards, hard drives), and make them not as powerful as superconducting magnets in MRI (Magnetic Resonance Imaging) machines.)

Online reading assignment: medium-mass stars, massive stars, neutron stars and black holes, keep-quit-start resolutions (SLO campus)

Astronomy 210, spring semester 2014
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 evolution of medium-mass stars, massive stars, neutron stars and black holes, and keep-quit-start mid-semester resolutions.

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 thought the comparison of the Hummer with the SmartCar was cool. I never thought about how they could go the same amount of range with the same tank. Crazy!"

The car range comparison, even though I still don't quite understand how it relates to the death of medium-mass stars."

"I find it interesting that when stars are dying they start to fuse heavier elements. And that's why those elements exist in our universe."

"What was interesting for me was looking at how a medium mass goes from being 'alive', eating through all its supply (like eating everything in your fridge), turning into a white dwarf and then finally exploding."

"It was interesting to learn that low mass stars take so long to die and especially that none have even died yet and that some are older than our galaxy."

"I thought learning about black holes was really interesting. That was something I was interested to learn about in the beginning of this class. The most interesting thing to me about black holes is that you can be falling in them forever. And the part about the event horizon and how once you get to that you're screwed, you can't get away. It's also crazy that we can't see them but we still have proof some how that they are still there."

"I liked the way that when medium-mass stars start to die they just steal from the star closest to them. I do feel bad for the star next to it though--it has no say in the matter."

"It was super interesting to read that basically one day the atoms that make us up are going to be in the nebula surrounding the sun when it dies in 5 billion years. I have never thought about life like that and it makes me feel better about dying one day because my atoms will be always be a part of the universe, even long after my body is decomposed."

"After going through the reading and the online presentation previews I found the topic of expansion cooling interesting. I found this topic interesting due to how the outer layers of the star expand and cool."

"I personally found it interesting when they were talking about the white dwarf star. And how they don't consider calling it a star, since it contains no gas. How they think it should really be called 'compact object.'"

"I think it was really interesting that a low mass star will last longer than a star with a larger mass. As well, that massive stars can become a black hole or a neuron star."

"Degenerate matter--how white dwarf stars are supported by it, it is super interesting and just epic."

"The expansion of medium mass stars into nebulae."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"How black holes can be difficult to discuss with others due to either believing or not believing that they truly exist."

"I don't understand the difference between all the types of explosions."

"I thought mainly the black holes were confusing because how can you say something is there when you can't even see it or we haven't even really found one. I know in theory we can prove they're there because we can see their effects, but how?"

"The most confusing thing for me was about the life and death of a star and the different kinds of stars and how they run out of stuff to 'eat' and convert differently. I am very confused about that and how to remember it and just what it means in the first place."

"How does one actually know what it's like to step into a black hole."

"It took me a while to understand how massive stars die. But once I understood it more I actually found it very interesting as well."

"I don't understand black holes. how do we see them, how do they work?"

"I'm kind of confused with the stars' mass and how they die because it was a lot to read and keep track of."

A Hummer H2 and a SmartCar ForTwo can travel the same distance with a full tank of gas. Briefly explain how this is possible.
"A SmartCar has a smaller engine but is more fuel efficient while a Hummer has a large engine but burns it up rapidly."

"The SmartCar has a better gas mileage but a smaller tank whereas the Hummer has a bigger tank but worse gas mileage."

"Because of the gravity."

Match the end-of-life stage with the corresponding main-sequence star.
(Only correct responses shown.)
Black hole: massive main sequence star [82%]
Neutron star: massive main sequence star [55%]
White dwarf: medium-mass main-sequence star [74%]
(No stellar remnant observed yet: low-mass main-sequence star [53%]

Match the type of explosion (if possible) with the corresponding main-sequence star.
(Only correct responses shown.)
Type II supernova: massive main sequence star: [95%]
Type Ia supernova: medium-mass main-sequence star [89%]
Nova: medium-mass main-sequence star [55%]
Low-mass main-sequence star: (no explosion possible) [68%]

If you were to leap into a black hole, your friends would typically watch you falling in for __________ before you entered the event horizon.
seconds.  ***** [5]
hours.  * [1]
days.  [0]
a year.  [0]
many years.  *** [3]
forever.  ************************* [25]
(Unsure/guessing/lost/help!)  **** [4]

The first rule of astronomy class is...
"...respect P-Dog?"

"...go to class?"

"...pretend like you're a professional astronomer--which would call for reading and doing homework."

"...quit procrastinating and start work sooner."

"...to answer all of the questions!

"...don't take P-dog's chillaxness for granted."

"...respect the goatee."

"...all hail the mighty gods of space."

"...don't waste food, that's not good science."

"...all of the tools are given to you, it's up to you to use them and succeed in this class."

"...you don't talk about astronomy class."

"...not show up late to the totally real house party."

"...what happens in astronomy class, stays in astronomy class."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Did you hear about the photo taken on Mars from NASA's Curiosity rover? It's a picture of the landscape on Mars and there's this unexplained light that people are speculating points to alien life." (...or periodic glitches from cosmic ray radiation, or shiny rocks. They see something like this about once a week.)

"Is it true that the Stephen Hawking has recently released statement saying that black holes don't exist?" (Actually his latest proposal is that our understanding of event horizons should be revised slightly with better quantum mechanical theories. Other physicists have different opinions on this.)

"Where does one buy that AstroBlaster toy?" (Amazon.com has them.)

"Have you considered possibly either going over the in-class activities before we turn them in or posting a 'key' online after class? A lot of us agree this would be helpful." (If you are uncertain of your answers even after checking with other groups, then make an effort to ask me questions to clarify these for you, either during the wrap-up whole-class discussion or after class ends (which I strive to finish at least slightly early so you can have time for this.)

"When I walk into your class my head always sings, Lady Gaga's 'Venus': 'take me to your planet, take me to your planet...'"

"Do you have any pets? Like that cat in the picture?" (Pocahontas has her own Facebook page. She posts about her housemates as well.)

20140408

Online reading assignment: medium-mass stars, massive stars, neutron stars and black holes, keep-quit-start resolutions (NC campus)

Astronomy 210, spring semester 2014
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 evolution of medium-mass stars, massive stars, neutron stars and black holes, and keep-quit-start mid-semester resolutions.

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 the black holes interesting because...its a black hole! If something is fast enough it can get away from its gravitational pull but if it isn't it just gets pulled into it!"

"The comparison of the two cars. It is interesting to think about how although one gets much better mileage, they both go the same distance."

"A low mass star will actually last much longer than a high mass star due to its fusion rate, I always thought it would be the other way around."

"I found the death of stars very interesting because they need that energy so much so that they will steal hydrogen from neighboring stars and cause them both to die...they are so selfish. they are like I'M TAKING YOU DOWN WITH ME!"

"Nuclear fusion. I am fascinated by the process happening within these stars, just because it's awesome and powerful beyond belief."

"I thought it was interesting that massive stars can either become a black hole or a neuron star after they die."

"I found time dilation interesting because is seems that with enough curvature of space, like that of a black holes, time could come to a complete stop. Makes me think of time as relative. Just depends on whether or not you're experiencing life inside a black hole or out."

"I knew stars 'died' but didn't know what actually caused their deaths."

"That everything that is heavier than iron was produced in a supernova. I find that interesting."

"It was interesting to learn the death of medium-mass stars. I didn't know some of the stars took so one to die and others were way faster."

I really liked reading about the black holes. I think it's super cool how there is a point of no return basically where you cannot outdo the pull which is the 'event horizon.'"

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Also black holes...I understand the concept of the gravitational force, but I didn't quite grasp the space-time curvature."

"Black holes are also really confusing and its hard for me to wrap my brain around it. Where does the light go and is anything existent behind it?"

"I found the black hole stuff confusing. I just dont get it at all"

"The event horizon of black holes. I am going back in the reading to try and straighten out the concept in my mind."

"How are black holes the most dense compact object?"

"Black holes. Stretching bodies. Falling into it forever. Weird."

Found density of a black hole hard to understand. How can something so small become so dense? Reading about it makes sense but just hard to conceive of in actual life."

I think it's confusing how black holes work and how the event horizon affects time."

"It was kinda confusing how the hummer and smart car both has the same range. But I think I see how that works. Pretty cool."

"I didn't understand what mass a black hole would be."

A Hummer H2 and a SmartCar ForTwo can travel the same distance with a full tank of gas. Briefly explain how this is possible.
"The Hummer H2 has a bigger fuel tank and wastes a lot of gas while the SmartCar has a little fuel tank but saves a lot of gas, so they both can travel the same distance."

"While the SmartCar has better mileage, it has a smaller tank and the difference comes out that they can both go the same distance on a tank of gas. One will just cost a lot more..."

"They can start off at a full tank of gas, but you may need to fill up that Hummer more often...or they are both on a trailer being pulled! ;)"

Match the end-of-life stage with the corresponding main-sequence star.
(Only correct responses shown.)
Black hole: massive main sequence star [71%]
Neutron star: massive main sequence star [33%]
White dwarf: medium-mass main-sequence star [58%]
(No stellar remnant observed yet: low-mass main-sequence star [42%]

Match the type of explosion (if possible) with the corresponding main-sequence star.
(Only correct responses shown.)
Type II supernova: massive main sequence star: [88%]
Type Ia supernova: medium-mass main-sequence star [58%]
Nova: medium-mass main-sequence star [63%]
Low-mass main-sequence star: (no explosion possible) [54%]

If you were to leap into a black hole, your friends would typically watch you falling in for __________ before you entered the event horizon.
seconds.  * [1]
hours.  * [1]
days.  [0]
a year.  * [1]
many years.  *** [3]
forever.  ********** [10]
(Unsure/guessing/lost/help!)  ********* [9]

The first rule of astronomy class is...
"...do your homework!"

"...read the book!"

"...everything is awesome! Everything is cool when you're part of a team!"

"...show up to class ready to learn and have a good attitude. At least that seemed like a good general rule to follow. Is this a trick question?"

"...uh, why are you called P-dog?"

"...don't show up late to the party."

"...dude, do not jump in black holes, that's dangerous."

"....you don't talk about astronomy class."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"Spacetime continuums freak me out, also they leave me inclined to believe in time travel."

"What are the chances of the Milky Way galaxy being sucked into a black hole?" (None, unless you are in the very tiny fraction of the galaxy that is already extremely close to the black hole to begin with, and wind up colliding with other stuff to slow down your orbital speed around the black hole. Otherwise, you're safe.)

"I'm sorry this weekend has kept me busy--I am so tired, and this will never happen again."