20130430

Online reading assignment: radioactive decay modes

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

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

The following questions were asked on reading textbook chapters and previewing presentations on radioactive decay modes.

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 the nucleus of the atom that is decaying simply want to be more stable and changes to become that and therefore emits some particle."

"It was interesting to read about the strong force and that it is responsible for holding the nucleus together."

"That protons can become neutrons."

"I like how this lecture seems kinda like chemistry."

"I find it interesting that we are learning the same thing in my chemistry class!"

"I found the PET scan image interesting and how when sugar molecules are ingested they can be configured to be metabolized only in certain tissues, and will then give off positrons in these regions as the fluorine decays."

"The cloud chamber demonstration was awesome. It was cool to visually see a half-life undergoing."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"The concept of stability has always been confusing to me, I know it seems simple with just certain numbers of protons and neutrons but i just get confused."

"Electron capture is a little fuzzy for me."

"I can't figure out what other particles are created when a proton turns into a neutron, and when a neutron turns into a proton."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I am confused on why 83 is this magic number of instability and why atoms with more protons than that will be unstable" (Actually, nobody seems to know from first principles why this number is so special--but taken that 83+ protons cannot be possibly be stable in a nucleus, nuclear physicists (and yes, nuclear chemists as well) come up with models that are consistent with this real-world observation.)

"I was a little confused that there are so many types of decay." (Because there are so many ways a nucleus can be unstable (having the wrong number of protons and neutrons), and many ways a nucleus can best reach a more stable combination of protons and neutrons within it.)

"If found it confusing to understand how proton turn into neutron and vice versa. I understand that a neutron will decay into a proton but I don't understand how a proton turns into a neutron." (Protons don't really want to be changed into neutrons, but can be forced to do so if it is for the benefit of the making the nucleus more stable. On the other hand, isolated neutrons outside of a nucleus will eventually turn back into protons, as there is no need to keep being a neutron.)

Astronomy current events question: Kepler-69e and Kepler 69f

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

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Michele Johnson and J. D. Harrington, "NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date," April 18, 2013
http://www.nasa.gov/mission_pages/kepler/news/kepler-62-kepler-69.html
NASA's Kepler space telescope discovered three super-Earth planets which may have oceans, as determined by their:
(A) lack of microwave emissions.
(B) reflectivity.
(C) distances from their stars.
(D) colors.
(E) infrared absorption.

Correct answer: (C)

Student responses
Sections 30678, 30679, 30680
(A) : 1 student
(B) : 7 students
(C) : 32 students
(D) : 2 students
(E) : 6 students

Astronomy current events question: Thirty Meter Telescope construction site

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

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Tim Hornyak, "Eye in the sky," April 14, 2013
http://news.cnet.com/2300-17938_105-10016452.html
Hawaii's Board of Land and Natural Resources __________ for the Thirty Meter Telescope atop Mauna Kea.
(A) approved the construction site.
(B) requested a size reduction.
(C) issued a volcano eruption warning.
(D) is holding a naming competition.
(E) will have all city streetlights turned off after midnight.

Correct answer: (A)

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

Astronomy current events question: dark matter detected?

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

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Camille Carlisle, "Homing in on Dark Matter," April 16, 2013
http://www.skyandtelescope.com/news/Dark-Matter--203199671.html
The Cryogenic Dark Matter Search (CDMS) collaboration detected possible three dark matter events from sensors:
(A) at old atomic bomb test sites.
(B) on the dark side of the moon.
(C) in a deep underground mine.
(D) downrange from the Large Hadron Collider.
(E) in an Antarctic research station.

Correct answer: (C)

Student responses
Sections 30678, 30679, 30680
(A) : 1 student
(B) : 6 students
(C) : 33 students
(D) : 5 students
(E) : 3 students

20130428

Astronomy quiz question: Milky Way capture of dwarf galaxies

Astronomy 210 Quiz 6, spring semester 2013
Cuesta College, San Luis Obispo, CA

__________ is evidence that small galaxies were captured by the growing Milky Way.
(A) Halo dark matter.
(B) The sun's absorption lines.
(C) Different ages of globular clusters.
(D) Stars orbiting the central supermassive black hole.

Correct answer: (C)

According to the monolithic collapse model, the Milky Way evolved from a spherical shape to its current disk shape, leaving behind the globular clusters out in its halo. Thus globular clusters should all have the identical (old) ages (as determined from the lack of metal absorption lines, and their H-R diagram turn-off points), while the disk should be comprised of mixed age (old and newer) stars. However, the presence of globular clusters of different ages indicates that they may have been inherited from smaller dwarf galaxies.

Section 30674
Exam code: quiz06Nu1N
(A) : 0 students
(B) : 1 student
(C) : 26 students
(D) : 1 student

Success level: 94% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0

Section 30676
Exam code: quiz06Sl6n
(A) : 7 students
(B) : 2 students
(C) : 24 students
(D) : 8 students

Success level: 65% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.41

Online reading assignment: radioactive decay rates

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

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

The following questions were asked on reading textbook chapters and previewing presentations on radioactive decay rates.

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.
"Radioactive decay as a whole interests me. We spent a large portion of CHEM 201B on it so it will be interesting to see it from a physics perspective."

"I thought that is was super interesting the probability of a given single M&M™ being eaten in a given time interval was not 0.5 and I can't explain why. :-( It caught my attention and boggled me."

"It was interesting to read about the radiocarbon dating because it offers such important data to our past."

"How independent identical (but unstable) nuclides are of each other."

"I thought that it was interesting how we will not be able to use carbon-14 as a way to date things in the distant future because we burn so much fossil fuel."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"The difference between the half-life and exponential decay expressions was a little confusing to me."

"It will be confusing looking at it from physics instead of a chemistry perspective because I spent so long learning it for chemistry! There are a bunch of new terms for stuff!"

"Where the equations come from are confusing, and why there is a natural logarithm within the half-life equation is still confusing to me."

"I was confused by quantum mechanical tunneling explaining radioactive half-lives for alpha decay. I'm not sure what is meant by tunneling or how it occurs."

"It will be confusing looking at it from physics instead of a chemistry perspective because I spent so long learning it for chemistry! There are a bunch of new terms for stuff!"

"I have to wonder how this model applies to something like depleted uranium. Depleted uranium munitions are thought to be part of the cause of 'Gulf War Syndrome,' which affects veterans of the first Gulf War, and even civilians from Iraq and Afghanistan from the current Gulf War. Depleted uranium comes mainly from spent nuclear fuel, and is valued as a munition for being denser than even lead. Supposedly, DU is melted and cast into munitions. How will this affect its half life and effect on human exposure?"
What is the mathematical relationship between τ and half-life for radioactive decays?
"τ is the decay constant while the half-life is the probability of decay per the unit time."

"τ is double the half-life."

"T1/2 = τ·ln(2)."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I liked the expression of using M&M™s to explain radioactive decay, but I didn't quite follow it. Everytime you toss them, some flip "m"-up and some "m"-down, but it is not necessarily even. The odds are sporadic and unpredictable. Radioactive decay is predictable, right?" (Only in the limit of a sufficiently large sample of unstable nuclei. If you were given only one unstable nucleus, knowing its half-life would only give you a probability of it decaying for the current time interval, regardless of how many time intervals it has survived up to present.)

"Can you go over why radioactive decay happens? Or what initiates it?" (That will be the top of the next presentation, but the short answer right now is that it has something to do with Jenga® and Ellen DeGeneres.)

"How hard is Midterm 2 compared to Midterm 1?" (About as difficult as quizzes 4-6 were to quizzes 1-3.)

"This is hard! There are only there weeks left in the semester!" (What?!? This is supposed to be the easy, fun stuff.)

20130427

Presentation: radioactive decay modes

Contrails in the sky, produced by airplanes passing through cold, water-saturated air. Airplanes pass overhead all the time, whether or not the sky just so happens to be cold and water-saturated. (Video link: "Chemtrail or Contrail bonanza time-lapse Amsterdam 2012.")

Contrails in a cloud chamber, produced by natural background radioactive decay particles passing through cold, alcohol-saturated air. Radioactive particles from natural background decays zing around all the time, whether or not the air just so happens to be cold and alcohol-saturated. (Video link: "large diffusion cloud chamber with radon gas double-decaying!.")

In this presentation we look into the causes of radioactive decays (compared to the previous presentation discussing the behavior of radioactive decays over time).

First, structure of atomic nuclei.

Each nucleus, whether stable or unstable, contains a set number of positively-charged protons and neutrally-charged neutrons. From chemistry, the specific element is denoted by its chemical symbol, and (somewhat redundantly) the atomic number of the element denotes the number of protons in the nucleus. The nucleon number denotes the total number of nucleons (protons and electrons), such that the number of neutrons is the difference between the nucleon number and atomic number.

Second, stability and instability of nuclei.

For all atomic nuclei, big and small, the key to stability is being able to keep the protons in the nucleus together, in spite of them all repelling each other. Having a certain number of neutrons in the nucleus will mitigate the proton-proton repulsion, and not just merely by spacing apart the protons.

A nucleus containing more than 83 protons will always be unstable, no matter how many neutrons there are, as there is just too much proton-proton repulsion.

For a nucleus with 83 or fewer protons, having too few neutrons than protons will be unstable. Also having too many neutrons than protons will also be unstable. But having the proper ratio of neutrons, approximately equal to or slightly greater than the number of protons, will make the nucleus stable.

The model of why neutrons are critical for keeping a nucleus stable is that there is a "strong force" that "sticks" nucleons together. This is an attractive, short-range contact force--think of velcro--that balances out the repulsive forces between the protons in a nucleus, and is a fundamentally different type of force than those covered in this course so far (gravitational forces, electromagnetic forces).

Related to the weirdness of the strong force is that a proton (which is intrinsically stable) can be transformed into a neutron, and vice versa (through processes we'll discuss later). Even more weird is that a neutron is intrinsically unstable--an isolated neutron outside of a nucleus has a half-life of 10.2 minutes, and will eventually decay back into a proton. Think of a stable nucleus as having protons continuously transforming into neutrons, and neutrons continuously transforming into protons, and as they are transforming back and forth into each other, the strong force "sticks" them together, balancing the repulsive force between protons. An unstable nucleus, then, also has protons transforming into neutrons and vice versa, but the wrong ratio of protons to neutrons does not optimize the amount of proton-neutron transformations--and thus strong force "stickiness"--that would balance the repulsive force between protons, such that the nucleus will eventually need to somehow undergo a process to reach a more stable configuration, whether by falling apart (fission), or ejecting small parts of itself, as in the modes of radioactive decay discussed below.

Third, the different processes that unstable nuclei can undergo to achieve more stable configurations, and applications of these different types of decays.

Alpha decay is how a nucleus with way too many protons achieves a more stable configuration. This is observed to happen by ejecting a blob containing two protons and two neutrons--thus, a helium nucleus--which reduces the number of protons in the nucleus, and this may occur a number of times as long as there are more than 83 protons in the nucleus.

Americium-241 (unstable americium with 241 nucleons: 95 protons and 146 neutrons) is used in a ionizing smoke detector, as it gives off alpha particles as it decays, and these positively charged particles are used to complete a circuit. Particles of smoke will also attract the alpha particles, and the presence of these in the vicinity of the detector will disrupt the flow of current in the detector, setting off an alarm.

Beta-minus decay is how a nucleus with too many more neutrons than protons achieves a more stable configuration. This is observed to happen by transforming a neutron into a proton (thus reducing the number of neutrons while increasing the number of protons). This transformation emits an electron--historically called a "beta particle" in the context of radioactivity--and a small, neutral particle called an antineutrino.

This is from my personal keychain.  Mrs. P-dog asks me if this why we don't have kids yet.  I tell Mrs. P-dog that when we do have children, they will have awesome mutant powers.
Helium-3 ("tritium," unstable helium with three nucleons: two protons and one neutron) is used in materials that glow in the dark without needing to be first exposed to sunlight. So instead of phosphorescent paint being conventionally excited by ultraviolet light, it is instead continuously excited day and night by the energetic electrons given off by the tritium as it undergoes beta-minus decay.

Beta-plus decay is how a nucleus with too few neutrons than protons achieves a more stable configuration. This is observed to happen by transforming a proton into a neutron (thus reducing the number of protons while increasing the number of neutrons). This transformation emits a positron--which is a positively charged antimatter "twin" of an electron--and again a small, neutral neutrino.

If you ever have a PET scan, think not just about drinking radioactive sugar water, but about antimatter and matter annihilating in your body!
Fluorine-18 (unstable fluorine with 18 nucleons: nine protons and nine neutrons) incorporated in sugar molecules is ingested by patients undergoing a positron emission tomography (PET) scan. The sugar molecule can be configured to be metabolized only in certain tissues, and will then give off positrons in these regions as the fluorine decaays. When an antimatter positron immediately runs into the first matter electron it encounters, this antimatter and matter pair will annihilate each other and give off two high energy photons that move off in directly opposing directions. By detecting and triangulating the specific regions in the body that keep emitting the pairs of photons from positron-electron annihilation, a three-dimensional metabolic map can be constructed.

(For the purposes of completing our discussion of beta decay, a third type is electron capture, where the nucleus will actually swallow an electron, in order to achieve a more stable configuration (and also emit a neutrino afterwards). Does this increase or decrease the number of nucleons in the nucleus? Does this increase or decrease the number of protons in the nucleus? Does this increase or decrease the number of neutrons in the nucleus? Is electron capture more similar to beta-minus decay or beta-plus decay?)

Gamma decay is how a nucleus achieves a more stable configuration, but not because it has too many protons, or the wrong ratio of protons to neutrons, which is what alpha and beta decays allow. After a stability-achieving alpha or beta decay, the nucleons in the nucleus may all still be too energetic, and can shed the excess energy in order to "calm down" by emitting a high-energy photon--historically called a "gamma ray" in the context of radioactivity.

There is an overlap between low-energy gamma ray photons and high-energy x-ray photons.  The distinction between them in this overlapping energy range is from their origin: a gamma ray photon, whether high or low energy, is emitted from an energetic nucleus, while an x ray photon, whether high or low energy, is emitted from quickly stopping a fast-moving electron.
Gamma rays are the most highly energetic type of photons, even more energetic an x-rays. This allows them to penetrate through thicknesses of metal that would be opaque to x-rays, allowing inspection of the interior of metal machine parts and shipping containers, as is done in mobile scanning unit.

So keep in mind that no matter what type of radioactive decay process occurs, a nucleus with an unstable configuration is merely seeking a more stable configuration. Just like Ellen DeGeneres. (Video link: "Best Game of Jenga Ever?")

Backwards faded scaffolding laboratory/presentation: poster session preview, preparation

Have you ever participated in a science fair? Posed your own research question, done your own research (this student apparently has done quite a bit of "research"), and displayed your results for all the world to see?

Same thing happens at real-world science conferences, although this is referred to as a "poster session," but pretty much the same idea as a science fair.

(This is the thirteenth Astronomy 210L laboratory at Cuesta College, San Luis Obispo, CA. This course is a one-semester, optional adjunct laboratory to the Astronomy 210 introductory astronomy lecture, taken primarily by students to satisfy their general education science transfer requirement.)

Let's take a look at what we'll be doing in the upcoming, final laboratory next week, and how to start preparing for it this week.

At a conference poster session, presenters and participants get to interact with each other and exchange constructive criticism...

...most importantly, face-to-face. In order to facilitate this valuable opportunity to mingle and network with colleagues, poster session organizers typically furnish refreshments and beverages.

Which is what we'll be doing next week--so before you leave today, write up on a whiteboard your proposal for an individual research question on some aspect of the concepts explored earlier this semester, get it approved along with a step-by-step procedure, and then complete your research report for homework before you come to the next laboratory.

We'll have a poster session then, so you'll be allowed space for nine letter size sheets in a 3 × 3 format (or equivalent-sized poster board) to present your findings.

20130426

Presentation: radioactive decay rates

This crane claw from Chernobyl? Hot. Totally hot. Hawt. (Video link: "chernobyl 2012 II the highly radioactive graphite crane claw (deja vu).")

But for how long? In this presentation we will consider the behavior of radioactive decays over time, while the next presentation will look into the causes of these radioactive decays.

First, M&M™s make friends. And makes a great model for radioactivity.

Pair up and grab a snack pack of M&M™s. Tear it open, and toss the contents on the table. Eat the M&M™s that show an "m" face-up, and don't eat the face-down. But before you eat any of the face-up M&M™s, count them! These will be the radioactive decays that happen each time interval.

Toss the remaining M&M™s, count and eat the face-up "m" M&M™s, and then repeat. Keep tossing, counting and eating, and repeat for each round.

We'll use these numbers later to mathematically model the "decay" of the class' M&M™s.

Second, mathematical models of radioactive decay.

We can write an exponential expression for the activity of these M&M™s, which is not the number of M&M™s that we have remaining during each time interval (as we typically cannot count the number of radioactive atoms in a sample), but the activity is the number of M&M™s that are eaten during each time interval (corresponding to the number of radioactive atoms that decay, which can be counted by a detector).

In this case, R0 is the initial rate of decays per second at t = 0. We can use a Wolfram Mathematica template with our M&M™ data to find an expression for the decay constant λ, which for a statistically large sample is the probability that a given single M&M™ will decay in a given time interval.

Related to decay constant λ is the time constant τ, which for a statistically large sample is approximately the average lifetime of a given single M&M™ before it decays (that is, eaten). (This is not one toss interval--can you explain why? And it is not merely because your class' sample of M&M™s may not be statistically large.)

The number of M&M™s that are eaten during each time interval can also be given in terms of an equivalent half-life expression, where the half-life T1/2 is the time for one-half of a statistically large sample to decay (which should be one time interval for the M&M™s--right?). (This half-life T1/2 is related to the time constant τ and the decay constant λ.)

Third, determining the "age" of a sample from its radioactive decay activity.

Consider this toy model of a substance that has radioactive atoms (represented by dark gray squares) and inert, non-radioactive atoms ("×" squares), which we will ignore for the purposes of discussion, as they do not participate in the radioactive decay process.

Each time interval on the clock displayed here is one half-life for the radioactive atoms to decay into a daughter atom (light gray squares). After one half-life, one-half of the original radioactive atoms remain; after two half-lives, one-quarter of the original radioactive atoms remain; so after three half-lives, one-eighth of the radioactive atoms remain. The key to determining the radioactive age of this substance is to assume that it started out with radioactive atoms with no daughter atoms (disregarding the amount of inert material), so the greater proportion of daughter atoms to radioactive atoms corresponds to an older sample.

Radioactive atoms used for this method of dating rocks decay into gaseous daughter atoms, which are trapped within the sample. When this sample is melted, then these gaseous daughter atoms are released and can be compared to the amount of radioactive atoms left in the molten sample (which can be inferred from the activity) to determine how long ago the sample started with radioactive atoms with no daughter atoms.

Note that after a molten sample solidifies, it will start anew with having radioactive atoms with no daughter atoms. So, melting a sample "resets" its solidification age--how long ago has it been since the sample started with radioactive atoms with no daughter atoms.

20130425

Astronomy quiz archive: Milky Way, cosmology

Astronomy 210 Quiz 6, spring semester 2013
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz06Nu1N


Section 30674
0- 8.0 :
8.5-16.0 :
16.5-24.0 : ********* [low = 16.5]
24.5-32.0 : ******** [mean = 28.2 +/- 7.6]
32.5-40.0 : *********** [high = 40.0]


Section 30676, version 1
Exam code: quiz06Sl6n


Section 30676
0- 8.0 : * [low = 5.5]
8.5-16.0 : ********
16.5-24.0 : *************** [mean = 21.1 +/- 5.9]
24.5-32.0 : ***************
32.5-40.0 : * [high = 36.5]

20130423

Online reading assignment: flux laws & devices

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

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

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

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.
"It was interesting to read about how transformers work because they are a part of our everyday lives and are important."

"I like how this is kind of a different way to figure out what we just did."

"I thought that the units given from a magnetic field passing through a perpendicular area was Webers. I have a family of friends called the Webers!! I love them!"

"I liked the floating candelabra, although I don't understand it."

"I thought that it was super interesting when the AAA battery lit up the 220 V bulb with a transformer."

"I really liked the idea of magnetic flux and Faraday's Law, they completely made sense to me."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"Faraday's law was a little hard to follow the way they had it in the textbook."

"When looking at the equations, I still don't quite get what 'Wb' is. Watts?"

"I down quite understand the transformers step-up and step-down business."

"Faraday's law is weird. I think I get it, But what exactly is being induced?"

"I still don't fully understand what happens in transformers or how generators turn magnetic fields passing through areas into emf."

"I honestly tried to read and understand the online presentation and I read the book but I was just lost for a majority of it. I don't feel like I understood much. I would really benefit going over this in class."

"'However, the current induced in a loop (because the external magnetic flux through it is changing over time) will be in the direction that creates a magnetic field that opposes the changes in the external magnetic flux.' I cannot wrap my head around this, I think I just need to see it."

"I think what is difficult has been keeping up with everything so far with magnetic fields and being able to recall fast enough to serve me well with what we are currently working with."
Describe what happens to a wire coil while the magnetic flux through it is changing.
"A coil experiences an induced current when the magnetic field passing through it varies."

"If the magnetic flux is changing then there is an induced emf of the wire coil."

"Heats."
Briefly describe what a transformer is supposed to "transform."
"Voltage up and down as a step-up or step-down transformer."

"A transformer transforms one level of voltage and current into another. A step up transformer raises voltage and lowers current, usually to make long power lines more efficient, and a step down transformer raises current and lowers voltage, usually to make it safe for homes and appliances."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"The levitating chandelier was cool. After further reading the blog post, I was reminded of wireless charging, which I think is induced charging rather than direct charging. This is why the bulbs light up, right?" (Right. You can even buy an aftermarket wireless charging kit.)

"How many cats do you have?" (Right now, only one--and she has her own Facebook page.)

Online reading assignment: history of atoms, Earth, the moon, Mercury (SLO campus)

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

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

The following questions were asked on reading textbook chapters and previewing presentations on history of atoms, Earth, and the impacted worlds: the moon, and Mercury.

Selected/edited responses are given below.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"I found the greenhouse effect to be interesting because I was able to visualize the concept since I know what a greenhouse is; plants can grow with the heat from the sunlight. I thought it was cool that it was also considered the 'parked car effect' since sunlight heats up a car, but the heat gets trapped."

"That the universe is in us..."

"How similar Earth is to the moon and nearby planets. Although entirely different, it's interesting seeing the similarities."

"I found it interesting how the moon is almost all crust with a smaller core than it thought it should have considering its size."

"After Earth formed and it was cooling the oceans formed which started dissolving carbon dioxide and removing it from the atmosphere it then reacted with dissolved compounds in the water to form limestone and other mineral sediments. I find this interesting because I have never thought about how these things were created and it is a very easy concept to understand and I guess I was just surprised by the information."

"The fact that volcanoes put carbon dioxide in our atmosphere but that oceans absorb a lot of it so it doesn't pollute our atmosphere too much."

"What was interesting to me was the history of atoms in our body. For example, atoms heavier than iron such as iodine were created by rapid nuclear reactions that only occur during supernova explosions. I found this really cool and interesting because I never knew this until now and I was always curious about what people were made of."

"I think it's interesting that if the moon and Mercury had formed in the same manner as Earth, then they would be expected to have the same size cores as Earth."

"I really liked the cute little comic strip!! I like the poetic appeal to it. I love Earth! :D"
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"The greenhouse effect was a little confusing, maybe just a little clarification."

"That the universe is in us..."

"It's not really confusing, but when the book says that all this stuff happened and everything is constantly changing, it's a little hard to grasp that. We live for 100 years at the most, while it takes years and years for a planet to form, for example. It's crazy."

"How certain theories apply to how planets were formed and how it is known."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"We are made of matter from the first 3 min of our universe?" (Only if you are primarily made of hydrogen, with a sprinkling of deuterium, helium, and lithium thrown in.)

"Is the reading suggesting that some or all moons are formed from high impact events?" (Only Earth and the moon, and Mercury.)

"I thought there were eight quizzes total and three would be dropped. It says there are only seven on the schedule though. I remember you mentioning this early on in the semester but I must have forgot." ("Quiz 8" is credit fir taking the educational research surveys in class.)

"I was recently told by a friend that the static that you can hear in between radio stations has something to do with the big bang. Do you know? " (About 1% or so of that static.)

"Do we need to know all the other planets rotations and angles that are exceptions to the natural rotation pattern in the solar system?" (Only that they are all more or less the same, except for the notably tilted-over axis of Uranus.)

"Neil deGrasse Tyson is the bee's knees, one of my favorite people to listen to/watch. Have you heard of the Joe Rogan Experience podcast? He interviews him in #310, free on iTunes [also on YouTube] if you ever want to kill 2.5 hrs in a long drive. Really entertaining to listen to his down-to-earth caliber as a hardcore astrophysicist!" (Neil is da man.)

Online reading assignment: history of atoms, Earth, the moon, Mercury (NC campus)

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

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

The following questions were asked on reading textbook chapters and previewing presentations on history of atoms, Earth, and the impacted worlds: the moon, and Mercury.

Selected/edited responses are given below.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.
"The moon and Mercury look alike in color and are covered with impacted craters. but different because Mercury has a larger core than the moon."

"I found the formation of Earth interesting and the process of the evolution of the atmosphere."

"The greenhouse effect. I didn't really understand it until now but the car example made it very clear."

"I found the comic strip interesting because Neil deGrasse Tyson is awesome. It was really cool the way he put things in perspective."

"We are a part of the universe. This is interesting, because: science."

"Learning about the origins of our atoms is amazing. Just thinking that stars made the iron in our bodies is amazing!"

"I had heard about the 'large-impact hypothesis' theory about the creation of the moon, but I didn't know that it produced lower density rock on the moon and also affected the rotation of Earth."

"That Mercury is only 40 percent larger than Earth's moon, and that it can't keep a permanent atmosphere. It sounds cool."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"I found plate tectonics confusing and the separation of plates on Earth."

"I kind of couldn't tell which feature on the moon was the youngest. Any advice on how I could tell which features are the youngest/oldest?"

"Mercury and the moon because i didn't know they were alike at all."

"Nothing was too confusing, it's weird because when you, P-dog, explain it in class is when I start to question things."

"The text seems to say that Venus would not have had its severe greenhouse affect if it had been able to retain water in an ocean and trap excess carbon there, but Venus was too close to the sun and couldn't keep its water. Is it really that simple? I thought that Venus was also in a habitable zone like Earth."

"What I found confusing in the assigned textbook reading is that they consider the moon as planet-like just because it's two-thirds the size of Mercury, and it is similar to Earth, Mercury, Venus, and Mars. Since they had said the moon was a natural satellite."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I never really know what to write here, so hi. I like how you teach, you're funny!" (Okay. Funny: ha ha, or funny: weird?)

"I was listening to Neil deGrasse Tyson and he was talking about antimatter. He said that if aliens came to us (assuming that they hadn't touch the ground yet) he wouldn't shake their hand. He would throw something to them to make sure that we are the same matter." (Neil is da man. Incoming!)

"How much water could comets have actually carried to Earth? It seems like it could only be a small amount." (The specific amount of water from cometary impacts, compared to the amount of water outgassed from Earth's volcanoes is still being investigated. In any case, most of Earth's atmosphere is thought to have been outgassed from its volcanoes.)

20130422

Astronomy current events question: naming exoplanets?

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

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Thierry Montmerle, Alain Lecavelier des Etangs, and Lars Lindberg Christensen, "Can One Buy the Right to Name a Planet?," April 12, 2013
http://www.iau.org/public_press/news/detail/iau1301/
The International Astronomical Union issued a public warning of an unauthorized organization collecting money to:
(A) repair the Hubble Space Telescope.
(B) broadcast messages to extraterrestrials.
(C) nominate and vote on exoplanet names.
(D) sponsor the International Space Station.
(E) name the asteroid NASA will bring to Earth orbit.

Correct answer: (C)

Student responses
Sections 30678, 30679, 30680
(A) : 2 students
(B) : 2 students
(C) : 45 students
(D) : 1 student
(E) : 1 student

Astronomy current events question: formation of Mars' early atmosphere?

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

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
Kevin Stacey, "Carbon's Role in Atmosphere Formation," April 8, 2013
http://news.brown.edu/pressreleases/2013/04/magma
Researchers investigated how magma in the moon and early Mars may have trapped and released atmospheric carbon by:
(A) analyzing sunlight reflected by the moon and Mars.
(B) using rovers on the moon and on Mars to drill into rocks.
(C) melting similar Earth rocks.
(D) creating lunar and Martian minerals from scratch.
(E) detecting fossil bacteria.

Correct answer: (C)

Student responses
Sections 30678, 30679, 30680
(A) : 7 students
(B) : 18 students
(C) : 19 students
(D) : 2 students
(E) : 5 students

Astronomy current events question: Transiting Exoplanet Survey Satellite (TESS)

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

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)
MIT Press Office, "NASA Selects MIT-Led TESS Project for 2017 Mission," April 5, 2013
http://web.mit.edu/newsoffice/2013/nasa-selects-tess-for-mission-0405.html
NASA selected the Transiting Exoplanet Survey Satellite (TESS) to launch in 2017 to detect exoplanets:
(A) while they form.
(B) as they orbit in front of their stars.
(C) being swallowed by dying stars.
(D) in neighboring galaxies.
(E) passing close to our solar system.

Correct answer: (B)

Student responses
Sections 30678, 30679, 30680
(A) : 1 student
(B) : 27 students
(C) : 1 student
(D) : 10 students
(E) : 11 students

20130421

Online reading assignment: generators

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

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

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

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.
"It was interesting to learn more about generators and how they create electricity, its just not what i had expected."

"I learned that the Space Shuttle tether generator is a single-use generator. I remember learning about this in high school, but I must've misunderstood, because I thought it was continuous generator revolving around Earth, rather than a single pass generator."

"I loved the video of the bike generator, because I ride a lot and do some spin classes. I always thought that attaching a generator to the wheel would be so cool."

"The continuous generators (Faraday disk, and rotating coil) were interesting because I had never seen them before, and wouldn't know how they work."

"The fact that you can touch an induction stove and not get burned, yet it can boil a pot full of water. We haven't gotten to the section that explains how this is possible, but I still find it fascinating!"

"A better understanding of motors. I knew you could flip them to make a generator, And I knew electromagnetic fields made them rotate."
Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.
"What the difference between an AC or DC generator was, how is the input/output reversed?"

"I was not aware of (or forgot about) single-pass generators. It is somewhat difficult for me to wrap my head around, as I always think of rotating things (continuous generators) with regards to generating electricity. What practical applications do single use generators have?"

"I am a little confused on how passing a rod through the middle of the magnetic field created by the moving emf makes the rod a battery."

"I thought a car starter could also act as a generator? I'll see you in office hours or something."

"I am still confused about differentiating voltage, amperes, current, energy, power, emf, etc. They all blur together in my mind."
Explain what a generator is supposed to "generate."
"A generator 'generates' electricity (turns the mechanical energy of motion into electricity)."

"Generators are suppose to generate current."

"They generate an emf."

"Power?"

"Everything a battery puts out."

"Volts or electrical potential difference."
Explain the meaning of "motional" in the term "motional emf."
"The 'motional' refers to a conductor actually moving through a magnetic field, or is in motion."

"I think that motional means that unlike a battery which is a chemical emf, the generators move to create the emf and current."

"MOVING."
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"≈:o" (See student comment below.)

"I think I might actually understand this section." (See student comment above.)

20130419

Physics quiz question: light bulb plugged into different voltage outlets

Physics 205B Quiz 5, spring semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Comprehensive Problem 18.113(d)

A 100 W light bulb plugs into a 120 V outlet. If this light bulb is (somehow) plugged into a 240 V outlet, it will draw __________ current and use __________ power compared to plugged into a 120 V outlet.
(A) less; less.
(B) less; the same.
(C) less; more.
(D) the same; less.
(E) the same; more.
(F) more; less.
(G) more; the same.
(H) more; more.

Correct answer (highlight to unhide): (H)

Assuming that the resistance R of the light bulb should remain (approximately) constant regardless of where it is plugged in, the current used by the light bulb in the 120 V outlet:

I240 = (240 V)/R,

should be more than the current when plugged into the 120 V outlet:

I120 = (120 V)/R.

The power used by the light bulb in the 240 V outlet:

P240 = (240 V)2/R,

will also be more than the power used in 120 V outlet:

P120 = (120 V)2/R.

Section 30882
Exam code: quiz05c4Rb
(A) : 2 students
(B) : 4 students
(C) : 4 students
(D) : 0 students
(E) : 2 students
(F) : 0 students
(G) : 6 students
(H) : 14 students

Success level: 44%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.27

Physics quiz archive: circuits (2)

Physics 205B Quiz 5, spring semester 2013
Cuesta College, San Luis Obispo, CA
Section 30882, version 1
Exam code: quiz05c4Rb



Section 30882 results
0- 6 : * [low = 6]
7-12 : ***********
13-18 : ********** [mean = 15.8 +/- 5.5]
19-24 : *********
25-30 : * [high = 27]

Backwards-faded scaffolding laboratory/presentation: impact craters (revised)

In Russia, nobody looks up at meteors--meteors look down on you. Video link: "Взрыв метеорита над Челябинском 15.02.2013.avi.")

(This is the eleventh Astronomy 210L laboratory at Cuesta College, San Luis Obispo, CA. This course is a one-semester, optional adjunct laboratory to the Astronomy 210 introductory astronomy lecture, taken primarily by students to satisfy their general education science transfer requirement.)

Let's first consider impact events from the distant, and also not-so-distant past.

Notably the "K-T" (Cretaceous-Tertiary) extinction event about 65 million years ago.

What would happen if you were a dinosaur living at that time? According to this artistic depiction, the ceratopsid on the left may have already perished from the blast wave, or maybe has just laid down due to the sheer despair of acknowledging its impending doom. Or maybe you would feel more like the plesiosaur on the right, either surfing its last killer wave, or asphyxiating from lack of oxygen.

Consider a much smaller event about a century ago in remote Siberia. The air blast from this event devastated the landscape below, fortunately far away from inhabited areas.

Whether there is an actual impact, air blast, or a near-miss, this sort of thing perhaps happens a bit too often for comfort...

So why wait around for the next impact event to happen on Earth?


Why not get some payback for the dinosaurs, which NASA got by punching a hole in a comet nucleus with a washing machine-sized solid copper projectile back in 2005?

Besides the obvious instant gratification, the science that can be done is in looking at the composition of the material flung out from the impact, in order to determine the ingredients of a comet. Also by making and freezing these ingredients, varying their compactness from fluffy to firmly packed, results from shooting projectiles into these lab samples can be compared with the size of the impact crater on the comet, in order to determine the type of cratering process in this material.

Which is what you get to do in laboratory today.

By dropping objects of different mass, or different height, you can create different energy impact events.

And you can measure the resulting diameters of these resulting impact craters.

By plotting the different impact energies versus impact crater diameters, you can determine the cohesion of a material, and the type of cratering process in this material.

Plotting different impact energies versus crater diameters should result in a linear data set, as graphed with "log-log" scales.

And by drawing a best fit line (not just "connecting the dots") for your data set...

You can slide a slope template to find the impact cratering process that best fits your data set.

EQUIPMENT
15 cm rulers (small, flexible)
meter sticks
material containers
medium-grain playground sand
coarse water softener salt
fine-grain table salt
baking soda
stainless steel balls
digital weight scales
hanging mass set (10 g, 20 g, 50 g, 100 g, 200 g, 500 g, 1000 g)

"Impact Energy vs. Crater Diameter Log-Log Graph"

"Impact Process Template"

BIG IDEA
Depending on the specific circumstances, an impactor will create a crater in a target material principally due to one of four processes:
  • Avalanche (splash): crater diameter set by how much material falls in around impactor.
  • Surface crack/pulverization (thud): crater diameter set by surface disturbed by impactor.
  • Compression (crunch): crater diameter set by material crushed beneath impactor.
  • Excavation (spray): crater diameter set by material thrown outwards by impactor.
GOAL
Students will conduct a series of inquiries about impact processes by varying different impactor and target parameters, and be able to quantitatively categorize different types of impact processes.

TASKS
(Record your lab partners' names on your worksheet.)
1. Exploration
  1. Carefully observe a stainless steel ball falling from 50 cm onto medium-grained sand, as measured from the top of the sand surface. Try this several times; note that you will need to cover your sand box and shake it vertically up-and-down a set number of times between each drop to consistently "reset" your sample surface between each drop.
    Discuss in your group the hypothesized process(es) of crater formation (i.e., "splash, thud, crunch, or spray," and briefly explain what you observed to support your choice(s). Do not worry about guessing the "correct" answer, this is just a preliminary hypothesis. You may note dissenting opinions, if any.

    Medium-grain sand crater process hypothesis: __________.
    Explanation of choice: __________.

  2. How the diameter of an impact crater is measured is a qualitative decision. Thus it is important to measure these diameters consistently. In order to do this, first make several trial impacts from different heights (do not record data yet), and discuss and agree in your group on a consistent description of a crater edge that can apply generally for impactors dropped from heights ranging from 10 cm to 100 cm, as measured from the top of the surface. Also record the mass of your stainless steel ball, in grams.

    Description/drawing of crater "edge" definition: __________.

    Mass of stainless steel ball: __________ g.

  3. Release (do not throw down) the impactor from 10 cm to 100 cm, in 10 cm increments, as measured from the top of the surface of medium-grain sand (in order to vary its energy), and measure its crater diameter. Make at least three drops for each height in order to test for consistent results. Then for each drop height, calculate the impact energy (in kiloergs) = (mass, in g)*(height, in cm), and the average crater diameter. (Example: a 50 g impactor released from 20 cm would have 50*20 = 1,000 kiloergs of impact energy.)

    Make a table compiling your drop heights (in cm), impact energies (in kiloergs), and crater diameters (in cm).

    Impactor
    height (cm):
    Impact
    energy (kiloergs):

    Crater diameters (cm):
    Average crater
    diameter (cm):
    10 cm
    _____, _____, _____.
    20 cm _____, _____, _____.
    30 cm
    _____, _____, _____.
    40 cm
    _____, _____, _____.
    50 cm
    _____, _____, _____.
    60 cm
    _____, _____, _____.
    70 cm
    _____, _____, _____.
    80 cm
    _____, _____, _____.
    90 cm
    _____, _____, _____.
    100 cm
    _____, _____, _____.

  4. Plot the data points from (c) on a group "Crater Diameter vs. Impact Energy Log-Log Graph," and use a ruler to draw a straight best-fit line across the entire graph.
2. Does Evidence Match a Previous Hypothesis?
The slope of your "Impact Energy vs. Crater Diameter Log-Log Graph" is related to the specific cratering process involved. Place the "Impact Process Template" over your graph, and slide it left or right while keeping the horizontal and vertical baselines aligned to determine which impact process slope is most parallel to your best-fit line.
Does your data support or refute your original cratering process hypothesis? Explain your reasoning and provide specific evidence from data to support your reasoning.

3. What Conclusions Can You Draw From This Evidence?
The table below summarizes the results of dropping different mass impactors, all from the same height (20 cm) into medium-grain sand.

Impactor
mass (g):
Impact
energy (kiloergs):

Crater diameters (cm):
Average crater
diameter (cm):
10 g
3.0, 3.0, 2.8, 3.0, 2.5 cm
20 g
3.0, 3.8, 3.3, 3.5, 3.5 cm
50 g
3.5, 4.2, 4.9, 5.0, 5.1 cm
100 g
5.0, 5.2, 5.5, 5.0, 5.4 cm
250 g
6.0, 7.0, 6.2, 5.8, 5.9 cm
500 g
7.0, 8.8, 8.2, 7.5, 8.0 cm

What conclusions and generalizations can you make from the information given above in terms of "Does varying impactor energy by varying mass (while keeping drop height constant), and by varying drop height (while keeping mass constant) give the same results for determining medium-grain sand cratering processes?" Explain your reasoning and provide specific evidence (a group "Crater Diameter vs. Impact Energy Log-Log Graph," with data points plotted, and best-fit line), to support your reasoning.

4. What Evidence Do You Need to Pursue?
Recall that you covered your sand box and shook it vertically up-and-down between each drop to consistently "reset" your sample. Consider the following claim:
"If the sand box is shaken side-to-side between each drop, the sand grains will sift and settle, becoming more tightly compacted for the next drop from the same height."
Describe precisely what evidence you would need to collect in order to answer the research question of, "How does a 'side-to-side reset' for medium-grain sand affect the results of each subsequent drop from the same height?" You do not need to actually complete the steps in the procedure you are writing.
Create a detailed, step-by-step description of evidence that needs to be collected and a complete explanation of how this could be done--not just "drop the ball multiple times," but exactly what would someone need to do, step-by-step, to accomplish this. You might include a (blank) table and sketches--the goal is to be precise and detailed enough that someone else could follow your procedure.

5. Formulate a Question, Pursue Evidence, and Justify Your Conclusion
Design an answerable research question), propose a plan to pursue evidence, collect data, and create an evidence-based conclusion about an aspect that you have not completed before. (Have your instructor approve your whiteboard research question before proceeding further.)
Research report summary on whiteboards/poster paper, to be worked on and presented to the class as a group, should include:
  1. Specific research question.
  2. Step-by-step procedure to collect evidence.
  3. Data table and/or results (including graph(s)).
  4. Evidence-based conclusion statement.


Procedure adapted from Gary Parker, "Low Velocity Impact Craters In The Lab," presented at Cosmos In The Classroom 2004 (*.html).