20170729

Astronomy in-class activity: planet-hunting

Astronomy 210 In-class activity 6 v.17.07.29, fall semester 2017
Cuesta College, San Luis Obispo, CA

Students find their assigned groups of three to four students, and work cooperatively on an in-class activity worksheet to determine where in the sky each naked-eye planet will be observed on a given date (here, September 6, 2017).




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20170602

Physics final exam question: voltmeter reading of leaking capacitor

Physics 205B Final Exam, spring semester 2017
Cuesta College, San Luis Obispo, CA

A capacitor is made from two parallel metal plates, and is charged with equal amounts of opposite charge. Both capacitor plates slowly lose their charge, due to being exposed to humid air. Discuss why the voltmeter reading attached to the capacitor decreases as this happens. Explain your reasoning by using the properties of capacitors, charge, electric potential, and energy.

Solution and grading rubric:
  • p:
    Correct. Explains why the voltmeter reading will decrease as the capacitor plates lose their charge, by discussing:
    1. that the capacitance must remain constant, as the plate area and the spacing between the plates remain constant; and
    2. because capacitance remains constant, then charge and voltage difference are proportional to each other, and thus a decrease in charge results in a decrease in voltage difference.
  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Does not explicitly discuss (1).
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying the properties of capacitors, charge, electric potential, and energy.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at applying the properties of capacitors, charge, electric potential, and energy.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 30882, 30883
Exam code: finalmR3x
p: 7 students
r: 8 students
t: 1 student
v: 5 students
x: 5 students
y: 0 students
z: 0 students

A sample "p" response (from student 4447):

Physics final exam question: induced current in loops surrounding vertical wire

Physics 205B Final Exam, spring semester 2017
Cuesta College, San Luis Obispo, CA


A vertical wire has a decreasing amount of current flowing upwards. Circular metal loops (of resistance R) oriented flat along the north-south direction are held by four different observers. Determine which observer (if any) will have a coil with an induced counterclockwise current, as seen in this perspective. Explain your reasoning using the properties of magnetic fields, forces, motional emf, Faraday's law and Lenz's law.

Solution and grading rubric:
  • p:
    Correct. Determines that only the north observer will experience a counterclockwise induced current, by discussing:
    1. right-hand rule 2, where the thumb runs along a straight current-carrying wire, and fingers curled around the wire give the direction of the magnetic field surrounding the wire; and
    2. from Faraday's law, the east and west observers have coils that will not receive any magnetic flux from the wire's current, so they will not observe any induced current in their coils; while the north and south observers have coils that are oriented to receive the changing magnetic flux from the wire's decreasing current, so they will observe an induced current in their coils; and
    3. from Lenz's law (and right-hand rule 3), only the north observer will experience a counterclockwise induced current to counter the decreasing flux that points east-to-west through it (while the south observer will experience a clockwise induced current to counter the decreasing flux that points west-to-east through it).
  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Correctly discusses (1)-(2), but has problems with discussing (3): typically may not have explicitly discussed why the magnetic field of the induced current in the north observer's loop must point in the same direction as the (decreasing) magnetic field from the wire, or determines that the south observer's coil will have a counterclockwise induced current.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete. At least some attempt at using magnetic forces and/or magnetic flux. Correctly discusses (1)-(2), but discussion of (3) is incomplete or missing.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying theproperties of magnetic fields, forces, motional emf, Faraday's law and Lenz's law.
  • x:
    Implementation of ideas, but credit given for effort rather than merit. No clear attempt at applying the properties of magnetic fields, forces, motional emf, Faraday's law and Lenz's law.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 30882, 30883
Exam code: finalmR3x
p: 1 student
r: 11 students
t: 2 students
v: 11 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 7117):

Physics final exam question: β+ decay of oxygen isotopes

Physics 205B Final Exam, spring semester 2017
Cuesta College, San Luis Obispo, CA

Unstable oxygen isotopes O(15,8) and O(19,8) can undergo some type of beta decay to become more stable[*]. Determine which one of these two isotopes (or both, or neither) will specifically undergo β+ decay. Explain your reasoning using the properties of nuclides and radioactive decay modes.

[*] wki.pe/Isotopes_of_oxygen.

Solution and grading rubric:
  • p:
    Correct. Recognizes that O(15,8) would undergo β+ decay, but not O(19,8) by discussing:
    1. a stable nucleus has a number of neutrons that are equal to or slightly greater than the number of protons; and
    2. β+ decay converts a proton to a neutron (by emitting a positron and a neutrino), decreasing the number of protons and increasing the number of neutrons in the nucleus; such that
    3. O(15,8) (which has seven neutrons and eight protons) undergoing β+ decay results in N(15,7) with a more favorable ratio of eight neutrons to seven protons), so β+ decay is possible for this oxygen isotope; while
    4. O(19,8) (which has 11 neutrons and eight protons) undergoing β+ decay results in N(19,7), which is a less favorable ratio of 12 neutrons to seven protons), so β+ decay is not likely for this oxygen isotope.
  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. May have only discussed why O(15,8) would undergo β+ decay, but does not discuss why O(19,8) would not.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete. At least understands β+ decay (and other weak interaction decays), but does not properly discuss how ratio of neutrons to protons affects stability.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying properties of nuclides and radioactive decay modes.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at applying properties of nuclides and radioactive decay modes.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 30882, 30883
Exam code: finalmR3x
p: 11 students
r: 5 students
t: 3 students
v: 3 students
x: 3 students
y: 0 students
z: 1 student

A sample "p" response (from student 3575):

Physics final exam question: valid or invalid Feynman diagram?

Physics 205B Final Exam, spring semester 2017
Cuesta College, San Luis Obispo, CA

Discuss whether this Feynman diagram is valid or invalid. Explain your reasoning using the properties of Feynman diagrams, particles and antiparticles, and interactions.

Solution and grading rubric:
  • p:
    Correct. Argues why this Feynman diagram is invalid by either one of two arguments:
    1. this process is not a proper permutation of a known weak interaction (as the nucleon changes into a lepton in the top path); or
    2. charge conservation is violated (zero charge of neutron does not equal the net positive charge of neutrino, positron, and proton out).
  • r:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.
  • t:
    Nearly correct, but argument has conceptual errors, or is incomplete. May argue why this Feynman diagram is invalid as does not correspond to a known weak decay process (but discussion of the known weak decay process is garbled); or argues that this Feynman diagram is valid as the "one line in, one line out" vertex rule is obeyed by both vertices (although charge conservation is violated, and the nucleon and lepton paths are mixed).
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying properties of Feynman diagrams, particles and antiparticles, and interactions.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at applying properties of Feynman diagrams, particles and antiparticles, and interactions.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 30882, 30883
Exam code: finalmR3x
p: 3 students
r: 3 students
t: 18 students
v: 2 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 7117):

Physics final exam problem: microscope object distance

Physics 205B Final Exam, spring semester 2017
Cuesta College, San Luis Obispo, CA

A NASA education guide for high school students[*] details plans for a simple microscope using an f = +28 mm objective lens and an f = +46 mm eyepiece lens, separated by a lens-to-lens distance of 160 mm. Determine the distance (in mm) that an object should be placed at in front of the objective lens for viewing through this microscope. Show your work and explain your reasoning by using ray tracings and/or thin lens equations, properties of lenses, images, and magnification.

[*] nasa.gov/pdf/350502main_Optics_Building_a_Microscope.pdf.

Solution and grading rubric:
  • p:
    Correct. Determines the object distance do1 for the objective lens by discussing:
    1. that the lens-to-lens distance is equal to the objective image distance di1 plus the eyepiece focal length f2 (as the image produced by the objective is placed at the focal point of the eyepiece), such that di1 = 160 mm − 46 mm = 114 mm; and
    2. knowing the focal point f1 = +28 mm and the image distance di1 = 114 mm for the objective lens, uses the thin lens equation to find the object distance do1 for the objective lens.
  • r:
    Nearly correct, but includes minor math errors.
  • t:
    Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. At least recognizes the placement of the intermediate image produced by the objective lens between the objective lens and eyepiece lens.
  • v:
    Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Garbled attempt at applying ray tracings and/or thin lens equations, properties of lenses, images, and magnification.
  • x:
    Implementation of ideas, but credit given for effort rather than merit. No clear attempt at applying ray tracings and/or thin lens equations, properties of lenses, images, and magnification.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 30882, 30883
Exam code: finalmR3x
p: 1 student
r: 1 student
t: 5 students
v: 14 students
x: 3 students
y: 1 student
z: 1 student

A sample "p" response (from student 7117):

20170601

Physics final exam problem: destructive interference angles in one quadrant

Physics 205B Final Exam, spring semester 2017
Cuesta College, San Luis Obispo, CA

Two vertical radio transmitters broadcast in phase at the same wavelength of 1.2 m, and are spaced a certain apart along the east-west direction. A Physics 205B student holding a receiver starts from due south of the transmitters, and detects three different locations with destructive interference signals before finally reaching due east of the transmitters. (Assume that each of the distances from the transmitters to the receiver are very large.) Determine a plausible separation distance (in m) between the transmitters. Explain your reasoning using the properties of source phases, path lengths, and interference.

Solution and grading rubric:
  • p:
    Correct. Discusses/demonstrates that three minima locations will be found in the range θ = 0° (due south) to 90° (due west) by using one of two approaches:
    1. using the destructive interference condition d⋅sinθ = (m + 1/2)⋅λ, where m = 0, 1, 2, ..., finds a plausible separation distance d such that the third minima (m = 2) will be within θ = 90°, but the fourth minima (m = 3) is outside of θ = 90° (i.e., 3.0 m ≤ d ≤ 4.8 m); or
    2. using the constructive interference condition d⋅sinθ = m⋅λ, where m = 0, 1, 2, ..., finds the separation distance d such that the third maxima (m = 3) will be at θ = 90°; which allows for the m = 0, 1, and 2 minima to exist within that range (i.e., d = 3.6 m).
  • r:
    Nearly correct, but includes minor math errors. May have claimed equally spaced minima angles at θ = 30°, 60° and 90° to find a plausible separation distance d using θ = 30° for the first minima angle.
  • t:
    Nearly correct, but approach has conceptual errors, and/or major/compounded math errors.
  • v:
    Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Garbled attempt at applying properties of source phases, path lengths, and interference.
  • x:
    Implementation of ideas, but credit given for effort rather than merit. No clear attempt at applying properties of source phases, path lengths, and interference.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 30882, 30883
Exam code: finalmR3x
p: 3 students
r: 4 students
t: 6 students
v: 7 students
x: 4 students
y: 2 students
z: 0 students

A sample "p" response (from student 0428), finding the maximum possible separation distance:

Physics final exam problem: ammeter and voltmeter readings

Physics 205B Final Exam, spring semester 2017
Cuesta College, San Luis Obispo, CA


A lithium battery with an emf of 3.6 V and an internal resistance of r = 0.45 Ω is connected to two light bulbs (each with different resistances), an ammeter, and a voltmeter. Determine (a) the ammeter reading (in amps) and (b) the voltmeter reading (in volts). Show your work and explain your reasoning using the properties of voltmeters, Kirchhoff's rules and Ohm's law.

Solution and grading rubric:
  • p:
    Correct. Determines the ammeter and voltmeter readings by:
    1. finding the equivalent resistance of the circuit, and then uses Ohm's law to determine the current passing through the 0.45 Ω resistor; and
    2. knowing the current and the resistance, uses Ohm's law to determine the drop in voltage across the 0.45 Ω resistor; and
    3. knowing the voltage rise of the emf and the voltage drop across the 0.45 Ω resistor, uses Kirchhoff's loop rule and Ohm's law to determine the current passing through the 1.2 Ω resistor, which is the ammeter reading; then
    4. knowing the voltage rise of the emf and the voltage drop across the 0.45 Ω resistor, uses Kirchoff's loop rule to determine the voltage drop across the 2.2 Ω resistor, which is the voltmeter reading.
  • r:
    Nearly correct, but includes minor math errors. Has determined at least one of (1)-(2), but only one of (3)-(4) is complete/correct.
  • t:
    Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. At least only one of (1)-(2) is complete/correct.
  • v:
    Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Garbled attempt at applying Kirchhoff's rules, Ohm's law, and properties of ammeters.
  • x:
    Implementation of ideas, but credit given for effort rather than merit. No clear attempt at applying Kirchhoff's rules, Ohm's law, and properties of ammeters.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distribution:
Sections 30882, 30883
Exam code: finalmR3x
p: 2 students
r: 2 students
t: 4 students
v: 2 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student):

20170525

Presentation: marketplace astronomy (results)

Let's compare your results with students from a previous semester. Here is the word tag cloud generated by Wordle.net for astronomy-related car makes and models. Frequently-listed cars are larger, while cars used only once are smallest. How many of these cars were you able to list? Anyone have cars not listed here?

Here is the word tag cloud for astronomy-related food brand names from a previous semester. Again, frequently-listed brands are larger, while brand names used only once are smallest. How many of these brand names were you able to list? Anyone have brand names not listed here?

Astronomy-related non-food brand names from a previous semester. Again, how many of these brand names were you able to list? Anyone have brand names not listed here?

Now we have potentially interesting astronomy topics from another previous semester. A lot of you are looking forward to learning about "black holes" this semester. Anyone have interesting topics not listed here?

And potentially confusing astronomy topics from another previous semester. "Black holes" is prominent here as well! Anyone have interesting topics not listed here? (Some of you may consider "math" as potentially confusing--yes, there is an algebra math prerequisite for this course, but there are no explicit calculations as we'll be focusing on graphs, dependencies, and proportionalities--essentially math without equations.)

And we have time to answer a few of your questions and comments.

"If you discovered a planet, P-dog, what would you name it?"
I would name it after my wife. I would name it: "Mrs. P-dog."
"Do you believe in aliens? Or life on other planets?"
Yes, and yes. I would bet money on it. I would bet $1. And I would win. But if I lost, it'd just be $1.
"Do you think Pluto should still be a planet?"
Let me tell you a story of my senior year in high school, way back when. I turned 18 during my senior year, and that was a big deal because you only needed to be 18 to be able to purchase and drink alcohol. My senior year was awesome. Commencement was awesome. Graduation parties were awesome...until a few years later, when the legal drinking age was raised from 18 to 21. And there was no grandfather clause. So before, it was legal for me to drink; but afterwards, I was no longer allowed to drink anymore. And that wasn't fair... So when it comes to Pluto, which was a planet, and then rules were changed so it is now no longer a planet, and there was no grandfather clause--I say, suck it up, Pluto.

Previous posts:

20170519

Online reading assignment question: advice to future students

Astronomy 210, spring semester 2017
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. The following question was asked after the last lecture, but prior to the final exam.

Tell a student who is about to take this course next semester what he/she needs to know or to do in order to succeed in this course. (Graded for completion.)
"Show up for class, do the reading assignments and don't miss the quizzes! Don't be afraid to ask questions, everybody can learn from them!"

"Don't miss any classes! Also, study as much as you can, otherwise enjoy working with P-dog."

"Read every chapter and all the presentations. Also review past quizzes and tests."

"Do homework! There isn't much but it is definitely worth it!"

"Be sure to read the chapters before you go to class and to practice certain things that P-dog gives to you."

"Go to class! Ask questions even if you think you sound dumb."

"Don't be close-minded, do your homework, and open your mind to all the wonderful aspects of our universe and knowledge."

"In order to succeed in this class is to ALWAYS show up, pay attention, read the book, and ask questions."

"First rule of astronomy class. Don't talk about astronomy class. Second rule. Find a partner who is good at what you aren't and don't just find a buddy to piss and moan with."

"In order to succeed, you must do the homework every week. If you do not, You WILL be lost when you come to class."

"Keep up because this class takes off running."

"Come to every class, especially if you have a hard time understanding the content!"

"Do all the readings and the homework. Study for the quizzes and midterms. Use all the resources that the teacher provides!"

"Do all the extra credit you can, because in the end those few points can make or break your grade. Always show up to every class because if you don't you'll be completely lost when you finally do. And always to the reading assignments, they are easy points and boost your grade as well. The cumulative point grade system is awesome! Thanks P-dog!"

"Go to class. It helps your grade and is fun. Confusing parts of the book are thoroughly explained when you ask."

"Just have basic knowledge about solar system planets and compass directions, as well as moon phases and everything should make sense and come together from there."

"Do well on the quizzes and then your grade on everything else will do better."

"Know the quiz information, do your home work, and relax its a good class!"

"Go to class because the lectures aren't boring, you don't exactly have to take notes, and the group activities help your grade. Do the homework because it is not stressful if you try your best and it helps your grade in the long run. Go to office hours to ask P-dog how to prepare for a quiz if you are unsure. He will help you prepare then and there."

"Always do the reading, and come to EVERY CLASS with questions."

"Attend class and take notes."

"Complete every single online reading assignment! Review pre class presentations, at least skim them! Study for quizes and save them to study for mid terms and finals! Do the extra credit opportunities. And DEFINITELY show up to class for in class activity points. Do this and you will get an A. It's easy!"

"Success is based on the amount of time you are willing to spend on the reading assignments which include book, and the online presentations, as well as showing up for every class and taking notes with your quiz packet in hand and already filled in. P-dog is very thorough with the material he supplies to make you a shining star."

"Do the reading assignments, read the book, study the quizzes."

"Do the work early, this class is made very convenient for you, everything you need to know is on the website. The reading assignments are informative and very creative. Also, don't be afraid to ask questions, this is the best class to ask questions in, and it can be confusing at some points, but P-dog makes it easy to understand and relatable."

"Do the online reading assignments before class."

"Do the reading and the online reading assignments! The reading is easy to do and most of the time you can get by without taking detailed notes or anything, and the assignment is really important because it previews what you'll be learning about next."

"Show up to class, every time. Take notes, participate in group work, do all of the readings and homework to prepare yourself for class, review often, and STUDY often."

"Don't ever be lazy in this class. It can be very easy to fall behind and just do the assignments before the next class but it is imperative that you read along in your book and complete every assignment, so the next class you know what is going on and ask questions for what you are lost on."