20080229

Leap year day t-shirts

Optical Illusion of Leap Year, by haxrox
shirt.woot.com

Several clever entries from Design Derby #30: Leap Year T-shirts at shirt.woot.com.

Come on Earth! Pick Up the Pace!, by KLSwoot
shirt.woot.com

Do the Math (First place derby winner) by Iambusyeating
shirt.woot.com

20080228

The cheerleader effect, part II

Colorado State University Cheerleaders
NBC Sports

Not exactly a true inverted pyramid (the top two cheerleaders are not standing on the shoulders of the bottom cheerleader, but a nice visual to motivate why the inner core of the Earth is hot, yet solid. See previous post discussing the "Cheerleader Effect" (hydrostatic equilibrium).

20080227

Sunshine vs. Little Miss Sunshine

Photoshop Phriday: Before and After Movies III, by Fenring
February 22, 2008
somethingawful.com

20080226

Astronomy midterm question: retrograde Mars

Astronomy 10 Midterm 1, spring semester 2008
Cuesta College, San Luis Obispo, CA

An observer in San Luis Obispo, CA notices that Mars is on the meridian at midnight. Discuss whether Mars is undergoing prograde (proper) or retrograde motion with respect to the background stars on that night. Explain your answer using a diagram showing the positions and motions of an observer, Mars, and Earth.

Solution and grading rubric:
  • p:
    Correct. Draws heliocentric orbits of Mars (outer) and Earth (inner), with Mars being on the meridian of a midnight observer located on Earth. Since Mars is at opposition, Earth is in the process of "lapping" it, resulting in Mars appearing to move retrograde (east-to-west, "backwards") with respect to the background stars. Diagram and discussion consistent, with some minor details omitted.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Diagram problematic/incomplete (e.g. Mars' orbit inside Earth's, or observer missing), but demonstrates some understanding of relative orbital motion and prograde/retrograde motion with respect to the background stars.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. Some attempt at explaining the "lapping" illusion to motivate retrograde discussion. May conclude prograde but diagram is otherwise correct.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distributions:
Section 4160
p: 15 students
r: 4 students
t: 5 students
v: 14 students
x: 1 student
y: 0 students
z: 0 students

Section 5166
p: 18 students
r: 4 students
t: 9 students
v: 35 students
x: 0 students
y: 0 students
z: 1 student

A sample "p" response (from student 1316):
This "p" response (from student 2431) explicitly shows the changing line-of-sight that Mars makes as it is "lapped" by Earth, resulting in retrograde motion with respect to the background stars:
Another "p" response (from student 2887), with anthropomorphized celestial bodies:

20080225

Astronomy midterm question: total lunar eclipse

Astronomy 10 Midterm 1, spring semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q2.4

At 7:30 PM at night, you are currently observing a total lunar eclipse in San Luis Obispo, CA. Suppose you decided to call a friend who lives in Seattle, WA, which is north of San Luis Obispo, CA. Explain what kind of eclipse (if any) your friend would be able to see in Seattle, WA at the same time, or why not, using a diagram of Earth, the moon, and shadow zones. Assume that the skies are clear in both San Luis Obispo, CA and Seattle, WA.

Solution and grading rubric:
  • p:
    Correct. Clear and correct diagram of the observer, Earth, the moon and the sun shown. For a total lunar eclipse, the moon is completely in the umbra of Earth. All observers on the night side of Earth will be able to see this total lunar eclipse. Note that a total penumbral lunar eclipse may be discussed instead, as long as all observers on the night side of Earth see the same thing.
  • r:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  • t:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. Earth-moon-sun diagram is essentially correct (showing a total lunar eclipse), but argument is based on observers being in different shadow zones, which is not possible, as all observers on the night side of Earth are in the umbra of Earth.
  • v:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Serious but flawed attempt at an Earth-moon-sun diagram, with major inconsistencies or errors, typically showing a total/partial/annular solar eclipse.
  • x:
    Implementation/application of ideas, but credit given for effort rather than merit.
  • y:
    Irrelevant discussion/effectively blank.
  • z:
    Blank.
Grading distributions:
Section 5166
p: 27 students
r: 4 students
t: 16 students
v: 18 students
x: 2 students
y: 0 students
z: 0 students

Notably this midterm was given during the umbral phase of the February 20, 2008 total lunar eclipse! Some students who had finished early were able to go outside and make Danjon L-scale ratings of the darkness of the umbral shadow on the Moon.

A sample of a "p" response (from student 0429) is shown below, clearly showing that observers in Seattle, WA and San Luis Obispo, CA would both see the Moon in the umbra of Earth:
Another "p" response (from student 1207) more elaborately illustrating the relevant geography:
Yet more elaborate geography in another "p" response (from student 1652):
An extended "p" response covering both total and partial lunar eclipse cases (from student 1886):

20080222

Astronomy midterm question: 18-hour work day

Astronomy 10 Midterm 1, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q2.2

[15 points.] It is remarked that when you are busy in Ukraine, you would typically work from sunrise to moonrise (The Week, volume 5, issue 212, pages 48-49). Explain which phase of the Moon would be seen to signal the end of approximately 18 hours of work, assuming that there are 12 hours between sunrise and sunset. Defend your answer using a diagram showing the positions of an observer, the Earth, Moon, and Sun.

Solution and grading rubric:
  • p = 15/15:
    Correct. Assuming sunrise at 6:00 AM, then end of 18-hour work shift would be at 12:00 AM midnight. "Phase 7," or the "third quarter Moon," or the "last quarter Moon" would rise at midnight.
  • r = 12/15:
    Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. At least clearly indicates that end of workshift is midnight, but has slightly incorrect phase for moonrise on east horizon at that time.
  • t = 9/15:
    Contains right ideas, but discussion is unclear/incomplete or contains major errors. As (r), but chooses full Moon, which is directly overhead at midnight.
  • v = 6/15:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
  • x = 3/15:
    Implementation/application of ideas, but credit given for effort rather than merit.
  • y = 1.5/15:
    Irrelevant discussion/effectively blank.
  • z = 0/15:
    Blank.
Grading distributions:
Section 4160
p: 10 students
r: 4 students
t: 12 students
v: 12 students
x: 1 student
y: 0 students
z: 0 students

A sample of a "p" response (from student 2887) is shown below:

Another "p" response (from student 4607) decries the hardships of the Ukraine work ethic:

20080221

Overheard: quiz before or after long weekend?

Physics 5A, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Physics 5A (college physics, algebra-based) at Cuesta College during Spring semester 2008 meets Mondays, Wednesdays, and Fridays. Quizzes (and midterms) are scheduled on Fridays. However, due to students getting both Friday and Monday off for a four-day weekend(!) to celebrate both Lincoln's and Washington's birthdays separately, the quiz normally scheduled for that Friday was moved forward to the preceding Wednesday, instead of the following Wednesday.

Conversation on the Monday before the quiz:

Student: "Why can't the quiz be pushed back to after the four-day weekend?"

Instructor: "If you're not ready for this quiz before this four-day weekend...you won't be ready for the quiz after the four-day weekend."

20080220

Physics quiz question: train coming to stop

Physics 5A Quiz 2, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 2.35(c)

[3.0 points.] A train is traveling 34.0 m/s in the +x direction when the brakes are applied. It slows down with a constant acceleration to a complete stop in a time of 110 s. How far has the train traveled at the end of 110 s?
(A) 617 m.
(B) 1.87e3 m.
(C) 3.74e3 m.
(D) 3.67e4 m.

Correct answer: (B)

Response (C) is the distance traveled by the train if it maintained its velocity of +34.0 m/s for 110 s. The correct response (B) is the distance traveled by the train with an initial speed of +34.0 m/s and a final speed of 0 m/s, for a constant deceleration during the 110 s. Response (A) is delta(t)^2/(2*g), and response (D) is v_ix*g*delta(t).

Student responses
Sections 4987, 4988
(A) : 1 student
(B) : 33 students
(C) : 12 students
(D) : 0 students

20080219

Physics quiz question: dropped golf ball

Physics 5A Quiz 2, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 2.45(b)

[3.0 points.] A golf ball is dropped from a building 180 m tall. Take upwards to be the positive vertical direction. Neglect air resistance. How far would the golf ball fall in twice the time it takes to fall 6.00 m downwards, if released from rest?
(A) –144 m.
(B) –36.0 m.
(C) –24.0 m.
(D) –12.0 m.

Correct answer: (C)

The displacement delta(y) is given by:

delta(y) = y_0 + v_y0*delta(t) + (1/2)*a_y*delta(t)^2.

Both y_0 and v_y0 are set to 0, and a_y = -9.80 m/s^2. With delta(t) twice as much as before, this term gets squared, resulting in a new delta(y) that is four times more than before.

Student responses
Sections 4987, 4988
(A) : 4 students
(B) : 10 students
(C) : 25 students
(D) : 7 students

20080215

Physics quiz question: average velocity

Physics 5A Quiz 2, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Conceptual Question 2.4

[3.0 points.] The chord slope of an x(t) graph is:
(A) the average velocity.
(B) the average acceleration.
(C) the change in (instantaneous) velocity.
(D) the change in (instantaneous) acceleration.

Correct answer: (A)

(Cf. "Physics chain of pain," an earlier post summarizing the graphical slope-area relations between kinematics graphs.)

Response (B) is the chord slope of a v_x(t) graph; response (C) is the area contained under an a_x(t) graph; response (D) is the area contained under a jerk(t) graph.

Student responses
Sections 4987, 4988
(A) : 24 students
(B) : 7 students
(C) : 14 students
(D) : 0 students

20080214

Valentine Dome, on Valentine Moon


Flickr.com: IMGP1525.JPG
Originally uploaded by Waifer X
February 14, 2008
Hand-held Pentax Optio S40, eyepiece projection shot through Orion SkyQuest 10" Newtonian reflector, Dobsonian mount, cropped to remove (most) vignetting. Mare Imbrium on the upper left, Mare Vaporum on the lower left, and Mare Serenitatis on the right, featuring the Valentine Dome (barely resolved). Fair-to-good seeing conditions at Cuesta College North County Campus, Paso Robles, CA. Click on the photo link for geographic (lunagraphic?) annotations.

20080213

Astronomy clicker question: telescope site selection

Astronomy 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal M1.4

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the end of their learning cycle:

[0.3 points.] Which one of the following choices best describes the least important consideration that astronomers look for when evaluating an observing site for a given electromagnetic radiation telescope?
(A) How clear the weather is at the site.
(B) How much atmospheric turbulence there is at the site.
(C) How far away the site is from Earth-based sources of that form of electromagnetic radiation.
(D) How transparent the atmosphere is to that form of electromagnetic radiation.
(E) How cold the temperature is at the site.

Correct answer: (E)

Students invariably make comments along the lines of, "astronomers can suck it up," when it comes through working in cold conditions.

Student responses
Section 4160
(A) : 0 students
(B) : 0 students
(C) : 0 students
(D) : 0 students
(E) : 30 students

20080212

Astronomy clicker question: most dangerous photon

Astronomy 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal M1.1

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the beginning of their learning cycle:

[0.3 points.] Which type of light ("electromagnetic radiation") particle is the most dangerous to be exposed to?
(A) A gamma ray photon.
(B) An x-ray photon.
(C) A microwave photon.
(D) (Each of these light particles (A)-(C) are equally dangerous.)

Correct answer: (A)

The energy of a photon is inversely dependent on wavelength; the gamma ray photon is the shortest wavelength of these photons, while the microwave photon has the longest wavelength. Many students explain picking gamma ray photons because of the origins of the Incredible Hulk. There may still be a concern with long-exposure to microwave photons, even though they contain the least amount of energy per particle, due to the number of photons involved.

Student responses
Section 4160
(A) : 19 students
(B) : 2 students
(C) : 1 student
(D) : 7 students

Section 5166
(A) : 26 students
(B) : 5 students
(C) : 3 students
(D) : 17 students

20080211

Education research: preliminary feedback on clickers (Cuesta College, Spring Semester 2008)

At the start of Spring semester 2008, Cuesta College students taking Physics 5A (college physics, algebra-based, mandatory adjunct laboratory) at Cuesta College, San Luis Obispo, CA have begun use of numerical keypad clickers (Classroom Performance System, einstruction.com) to enter homework and to engage in peer-interaction discussion questions during lecture.

During the third week of instruction, students were given the opportunity to evaluate the instructional components of the course, and the use of clickers in an online "Learning Resource Survey" hosted by SurveyMonkey.com. Questions from section II are adapted from the Student Assessment of Learning Gains (SALG) survey (developed by Elaine Seymour, Wisconsin Center for Education Research, University of Wisconsin-Madison), and questions from section III (III.1, III.3, III.5, and III.7) were adapted from a "Clicker Attitude Survey" (N. W. Reay, Lei Bao, and Pengfei Li, Physics Education Research Group, Ohio State University).

These are the complete survey results, with some preliminary commentary. No statistical analysis was done, but will be forthcoming after more data has been compiled at the end of this semester. Values for the mean and standard deviations are given next to the modal response category for each question. Note that the order of questions within sections II and III were randomly scrambled for each student.
Learning Resource Survey
Cuesta College
Physics 5A Spring Semester 2008 sections 4987, 4988
(N = 33)

I. In order to receive credit for completing this survey,
first enter your first and last name below:
____


II. How much did each of the following aspects of the class help your learning?

II.1 Lecture by instructor.
1. Strongly disagree 0 :
2. Disagree 3 : ***
3. Neutral 8 : ********
4. Agree 16 : **************** [3.8 +/- 0.9]
5. Strongly agree 6 : ******

II.2 Doing assigned homework, to be entered using clickers.
1. Strongly disagree 1 : *
2. Disagree 5 : *****
3. Neutral 4 : ****
4. Agree 16 : **************** [3.7 +/- 1.1]
5. Strongly agree 7 : *******

II.3 Doing unassigned homework.
1. Strongly disagree 2 : **
2. Disagree 2 : **
3. Neutral 9 : *********
4. Agree 15 : *************** [3.6 +/- 1.0]
5. Strongly agree 5 : *****

II.4 Using clickers to participate in class.
1. Strongly disagree 4 : ****
2. Disagree 2 : **
3. Neutral 6 : ****** [3.4 +/- 1.1]
4. Agree 18 : ******************
5. Strongly agree 3 : ***

II.5 Reading the textbook.
1. Strongly disagree 0 :
2. Disagree 3 : ***
3. Neutral 6 : ******
4. Agree 16 : **************** [3.9 +/- 0.9]
5. Strongly agree 8 : ********

II.6 Demonstrations/videos in class.
1. Strongly disagree 0 :
2. Disagree 1 : *
3. Neutral 8 : ********
4. Agree 21 : ********************* [3.8 +/- 0.6]
5. Strongly agree 3 : ***

II.7 Interacting with other students during class.
1. Strongly disagree 1 : *
2. Disagree 4 : ****
3. Neutral 7 : *******
4. Agree 17 : ***************** [3.6 +/- 1.0]
5. Strongly agree 4 : ****

II.8 Interacting with other students outside of class.
1. Strongly disagree 1 : *
2. Disagree 5 : *****
3. Neutral 15 : *************** [3.4 +/- 1.1]
4. Agree 5 : *****
5. Strongly agree 7 : *******

III. Answer the following statements which may or may not describe your
beliefs about the use of clickers in this class.

III.1 I like using clickers.
1. Strongly disagree 3 : ***
2. Disagree 3 : ***
3. Neutral 9 : ********* [3.4 +/- 1.1]
4. Agree 15 : ***************
5. Strongly agree 3 : ***

III.2 Clickers helped me understand lectures better.
1. Strongly disagree 5 : *****
2. Disagree 5 : *****
3. Neutral 12 : ************ [2.9 +/- 1.1]
4. Agree 11 : ***********
5. Strongly agree 0 :

III.3 I would recommend using clickers in future semesters of Physics 5A.
1. Strongly disagree 3 : ***
2. Disagree 2 : **
3. Neutral 11 : *********** [3.4 +/- 1.1]
4. Agree 14 : **************
5. Strongly agree 3 : ***

III.4 I will avoid other classes using clickers in future semesters.
1. Strongly disagree 6 : ******
2. Disagree 15 : *************** [2.4 +/- 1.1]
3. Neutral 7 : *******
4. Agree 3 : ***
5. Strongly agree 2 : **

III.5 Clickers were a positive experience.
1. Strongly disagree 2 : **
2. Disagree 3 : ***
3. Neutral 10 : ********** [3.4 +/- 1.0]
4. Agree 16 : ****************
5. Strongly agree 2 : **

III.6 Too much time in class was spent using clickers.
1. Strongly disagree 4 : ****
2. Disagree 14 : **************
3. Neutral 5 : ***** [2.8 +/- 1.3]
4. Agree 5 : *****
5. Strongly agree 4 : ****

III.7 Too many clicker questions were asked.
1. Strongly disagree 1 : *
2. Disagree 17 : *****************
3. Neutral 10 : ********** [2.6 +/- 0.9]
4. Agree 4 : ****
5. Strongly agree 1 : *

III.8 Clickers should be used to collect assigned homework.
1. Strongly disagree 4 : ****
2. Disagree 3 : ***
3. Neutral 9 : ********* [3.2 +/- 1.1]
4. Agree 15 : ***************
5. Strongly agree 2 : **

III.9 Using clickers was difficult.
1. Strongly disagree 13 : *************
2. Disagree 17 : ***************** [1.7 +/- 0.6]
3. Neutral 3 : ***
4. Agree 0 :
5. Strongly agree 0 :
Tthe responses in section III are generally positive towards the use of clickers. Some students were initially enthusiastic regarding clickers, but a vocal minority strongly expressed their comments below, especially with regards to cost and/or usefulness.
IV. (Optional.) Please type in any comments you may have regarding the use 
of clickers in Physics 5A.
The following are all of the student responses to this question, verbatim and unedited.
"They are cool except hard to make sure sig figs are right when 
trying to type in scientific notation. But overall cool!"

"it's something new to me and i like it it keeps class
interesting and is a unique way of learning and processing
information."

"Easy to use, fast, and interesting to see the different
answers of the class."

"They work just fine to convey our thoughts to the teacher.
However I feel that they often times disrupt the flow of
instruction which I beilieve is very important. The fact
that it is required makes it more difficult to enjoy
knowing it doesn't improve the learning enough for 20 or so
dollars spent on it.I feel it great tool to gather
valuable data fron students to improve educational
methods. However I ask at what cost? I believe the
instruction time lost and the opportunities for negative
learning experience out way the benefits.I think they
would be best used for surveys or group assignments were
time is set aside specifically their use. Clickers
should not be mandatory and students should be paid to
participate in any data collecting processes. Private
companies who sell ideas,programs or methods founded on
data collected from students should compensate students."

"The only downside is clicker style answers don't often
show thought processes that went into solving the answer,
however the use of participation points vs. correct points
is a nice addition to the class experience. Keeps the
students paying attention without penalizing them for
mistakes."

"the best thing about the clickers is not having to get
up and try to get around everyone to turn stuff in."

"I don't like the clickers at all. I feel that it takes
valuable time away from the lecture. Our lecture is only
an hour long and the clickers waste a lot of this very
valuable time. The only positive aspect of the clickers
is that it is an easy way for the professor to get
everyone to participate. Without the clickers, it tends
to be the same group of people answering the questions
every class session. Also, I suppose it allows the
professor to gauge where the class stands. Both of these
do nothing to help the class learn. They are a waste of
valuable class time, please get rid of them!"

"I fell that some of the clicker questions are unclear."

"I feel that the cllickers is a good way to see how
others in the class are responding but they do not
involve active discussion about the toopic on hand.
It is a bit isolating using clickers in my opinion.
I would not like to use them during lectures but for
homemork it is nice."

"I think that sometimes we spend too much time
worrying about clicker questions instead of
understanding what is being covered in the lecture.
However, the clickers do provide a welcoming way to
participate with the class."

"I think the clickers are a great, however, I believe
that we spend too much time on them and letting us take
to o try and comprehend the material."

"I really think they are a waste of time. Its great that
you get easy points but there has to be another way of
giving credit. I was very upset at how much they cost
plus registration because I did not get a new $144 book
I instead am borrowing a friends. It is a rip off to
the struggling students like myself. What happened to
the good ol' days of raising hands?"

"Clikers are ok but I think I learn more with the teacher
giving a lecture. Clickers are good in the sense that it
gives everyone a chance to participate and it helps
retain the focus of everyone. When homework is assigned,
we give our answers back in clickers, I think thats a
good idea, but then to also go over any questions that
we may have with any of the homework as well."

"I think it's a great way to get a pulse on all the
students in a large class and for the students themselves
to participate in the lecture, which helps in learning."

"The class gets broken up by using the clickers and
waiting for everyone to enter their answers. It would
work better for me if the teacher would lecture and use
class to answer questions verbally. The class lecture
could be more fluid if it was not broken by the clicker
entry sessions or the fact that the entire class does not
know what the answers are most of the time. If more time
was spent on the matterial than on the questions then
maybe we could learn from the lectures instead of on our
own with the book that some of us can not afford at
around $200."
The evolution of these opinions will be tracked when this survey is administered to students later this semester.

Previous posts:

20080208

Astronomy clicker question: planet-hunting

Astronomy 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q3.1

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the end of their learning cycle:

[0.3 points.] How can you determine if a bright object in the sky is a planet (and not a star), without using a telescope?
(A) If it does not twinkle.
(B) If it does not show up on a starwheel.
(C) If it does not appear in exactly the same location in the sky each night.
(D) (All of the above choices (A)-(C).)

Correct answer: (D)

The large angular diameter of planets make them less susceptible to atmosphere turbulence, so they do not seem to "twinkle" like point-like stars (response (A)). Planets also move with respect to the background stars as they (and the Earth) move around the Sun, and thus cannot be permanently positioned on a starwheel (responses (B) and (C)). Thus the most correct, inclusive answer is (D).

Student responses
Section 4160
(A) : 6 students
(B) : 1 student
(C) : 10 students
(D) : 13 students

20080207

Astronomy quiz question: Moon rise times

Astronomy 10 Quiz 2, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q2.2

[3.0 points.] An observer in San Luis Obispo, CA observes that the Moon rises in the east at exactly 6:00 PM. Which one of the following choices best describes the time that the Moon will rise in the east, on the following evening?
(A) Nearly an hour earlier than 6:00 PM.
(B) Exactly 6:00 PM.
(C) Nearly an hour later than 6:00 PM.
(D) (It cannot be determined when the Moon will rise the following evening, unless the date/season is given.)
(E) (It is impossible in San Luis Obispo, CA for the Moon to rise at 6:00 PM.)

Correct answer: (C)

As seen from above, the Moon revolves counterclockwise in its approximately 29 day-orbit around the Earth, while the Earth rotates counterclockwise in approximately 24 hours. Thus the Moon will have moved approximately 1/29th further along its orbit by the time an observer on the Earth notices it is rising again, and thus the Moon will appear to rise slightly later each consecutive day.

Student responses
Section 4160
(A) : 8 students
(B) : 5 students
(C) : 16 students
(D) : 9 students
(E) : 1 student

Student responses
Section 5166
(A) : 12 students
(B) : 13 students
(C) : 28 students
(D) : 12 students
(E) : 1 student

20080206

Astronomy quiz question: monthly solar and lunar eclipses

Astronomy 10 Quiz 2, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q2.4

[3.0 points.] Which one of the following choices best describes what would happen if the orbit of the Moon around the Earth was not tilted with respect to the orbit of the Earth around the Sun?
(A) There would never be any solar or lunar eclipses of any type.
(B) There would only be annular solar eclipses, and partial lunar eclipses.
(C) There would be a solar eclipse and a lunar eclipse every month.
(D) The Moon would then always block the Sun, making a permanent solar eclipse.
(E) The Earth would then always be between the Sun and Moon, making a permanent lunar eclipse.

Correct answer: (C)

The reason why there is no solar eclipse and lunar eclipse every month is that the orbit of the Moon around the Earth is tilted, such that the new Moon does not usually pass directly between the Sun and the Earth, and the full Moon does not usually pass directly between the Earth and the Moon.

Student responses
Section 4160
(A) : 4 students
(B) : 6 students
(C) : 25 students
(D) : 1 student
(E) : 3 students

Student responses
Section 5166
(A) : 5 students
(B) : 6 students
(C) : 50 students
(D) : 3 students
(E) : 2 students

20080205

Physics quiz question: joule heating power

Physics 5A Quiz 1, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Comprehensive Problem 1.72

[3.0 points.] The electrical power P drawn from a generator by a light bulb of resistance R is P = V^2/R, where V is the line voltage. The resistance of bulb B is 75% greater than the resistance of bulb A. What is the ratio P_B/P_A of the power drawn by bulb B to the power drawn by bulb A, if the line voltages are the same?
(A) 0.33.
(B) 0.57.
(C) 1.3.
(D) 1.8.

Correct answer: (B)

P_A = (V_A)^2/R_A, and P_B = (V_B)^2/R_B.

With V_A = V_B, and 1.75*R_A = R_B, then:

P_B /P_A = ((V_B)^2/R_B)/((V_A)^2/R_A) = (V_B/V_A)^2 = (R_A/1.75*R_A)^2 = (1/1.75)^2 = 0.57,

to two significant figures.

The incorrect response (A) is (1/1.75)^2, response (C) is (1/0.75), and (D) is (1/0.75)^2.

Student responses
Sections 4987, 4988
(A) : 8 students
(B) : 17 students
(C) : 13 students
(D) : 12 students

20080201

Physics quiz question: addition/subtraction rule

Physics 5A Quiz 1, spring semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 1.16

Evaluate the following calculation, using an appropriate number of significant figures and/or decimal places.

66.0 kg + 12.74 g = ?

(A) 66.0 kg.
(B) 66.01 kg.
(C) 66.01274 kg.
(D) 78.7 kg.

Correct answer: (A)

12.74 g is 0.01274 kg, with five decimal places. However, when added to 66.0 kg, which has only one decimal place, the result is 66.01274 kg (response (C)), which must be rounded to one decimal place (using the addition/subtraction rule, that restricts decimal places to the value with the least amount) to become 66.0 kg! Response (B) is rounded to two decimal places, while response (D) is the result of not converting 12.74 g to kg before adding.

Student responses
Sections 4987, 4988
(A) : 24 students
(B) : 5 students
(C) : 3 students
(D) : 18 students