Physics 2020: Fall '12

General Physics 2 (Electricity & Magnetism, and Optics)

MWF 11:00-11:50 Duane G1B20 (Section 100)

Exams and Grades

EXAM 3 info is now below ....

EXAM 2 now graded , see below .

EXAM 1 is now graded, see below for details!

General information:

If you miss more than 1 lab, or the final, you can't receive a passing grade!

We will use iClickers during lectures, to help you learn the material. Your iClicker responses count only as bonus (extra credit) points: they REDUCE exam weight by up to a max of 14% of midterm exam total (i.e. 5% of your course grade).

Detailed course grade information is available here
For further information, please see the Syllabus.
Second midterm is Thursday Oct 25, 7:30 - 9:15, in our regular classroom.

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MIDTERM #3 info:
Physics is inherently "cumulative", so material from Exam 1 and 2 could and will certainly reappear on this test! However,
the primary focus on Exam 3 is newer material covered since the first midterm, basically Ch 20-22 of our text. The main emphasis is on magnetic fields and forces, Faraday's (and Lenz') law, electromagnetic waves and light, and all the related ideas around those, as well as older (important!) stuff like voltage, E-field, capacitance, etc.

Note that Geometrical optics (Snell's law, mirrors, lenses, etc) is NOT going to be on this midterm, that will be on the final. So, Ch 23 material and beyond is not on this one. (That's lecture 34 and beyond)


Students who have informed us about their academic needs for special accomodation during the exam, will receive an Email about their Exam location. If you expect such an arrangement but did not receive an Email, please contact Prof. McElroy (not Prof. Pollock) ASAP!!

You may bring THREE SIDES (front and back of one, front of a second) of 8.5 in. x 11 in. paper for the third exam, with your own handwritten notes (written by you!) Calculators with scientific notation are allowed and sometimes needed. (Of course, no phones, internet access, "electronic crib sheets", etc!). We trust you to understand and follow the CU honor code. Please respect that trust! It's a large class, and we realize there may be some temptations - we are doing our best to make this class valuable and worthy of your honorable behaviour.

The exam will be similar in format to the first two, with multiple choice and long answer questions. (The # and balance of those will again be slightly different)

 

As always, anything covered in class, the text, lecture notes, CAPA or written homeworks, or labs is all fair game.

Note: we skipped Ch 20.8, 21.9-14, and 22.5-6, that material will not be on the exam.

Ch 20 Magnetism: You should ...
- know the basic B-field pattern of a magnet (a dipole field), of a long wire, and of a small loop of wire (I called this "Right Hand Rule 1b)
- know the attraction/repulsion story of N- and S- poles, and of current-carrying wires (the latter quantitatively)
- be able to superpose 2 (or more) B-fields to get the total field, as vectors.
- correctly predict the direction of B field around a long wire (first right hand rule).
- compute the B field around a long wire, a distance away from it.
- correctly predict the direction of the force on a moving charge, OR the force on a current-carrying wire or wire segment, in the presence of an external B field (2nd right hand rule)
- know and be able to use and interpret the "Cyclotron" formula (radius of the curved path of a charged particle in a B field), as well as the "velocity selector" formula, v = E/B (what it is, where it comes from, when it applies, how to use it)
- know that B-fields do no work (and why not!), and be able to qualitatively describe the path of a charged particle in a B field (e.g. the helical motion story)
- understand the physics of motors qualitatively (which way is the torque, given the current and B-field)
- have a qualitative understanding of how a bar magnet (or a current loop) aligns in an external field (which way does it line up? why?) and apply this to a magnetic material (like iron) to have a very basic (qualitative) understanding of how a permanent magnet works.

CH 21: Faraday's Law. You should...
- be able to compute magnetic flux, including a clear understanding of which angle "theta" is in that formula
- know Faraday's law quantitatively and qualitatively, and be able to apply it to compute the induced EMF in situations where flux changes. (and to recognize situations where flux is not changing)
- understand Lenz' law, to be able to predict the direction of induced current flow in any situation where flux changes in a loop (or to realize which situations do NOT yield current flow)
- Qualitatively describe/understand the basic physics of electric generators (including being able to apply the EMF formula 21-5 of your text)
- Qualitatively describe/understand the basic physics of "eddy currents", and the effect they have on the motion of metals in the presence of a B-field.
- Know and be able to apply the basic "transformer" formulas, including computing output voltage from input (or vice-versa), use and apply "conservation of energy" for transformers, and know (and be able to explain or apply) the fact that why transformers only works for AC situations, not DC
Ch 22, EM Waves and Light. You should be able to...
- Qualitatively describe how EM waves arise
- Know and use the (constant!) speed of light to compute travel times
- Know and use the relationship between wavelength of light, frequency, and speed.
- Have a qualitative understanding of the "spectrum" of EM waves, and be able to compare and contrast EM waves of different frequencies or wavelengths (including the fact that all such waves still have the same speed)

 

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More information about exam 2 (study guide, etc) is on this saved older page.

The class did great on exam #2!! Hiere is a histogram of class results on exam #2:

Ex2 histogram

- The average score was 80%. This is good work, the test was not easy!
- The median was just below 84% (That means half the class scored above 84%!)
- The "Standard Deviation" was 15.5%.
- We don't assign letter grades to exams. Only your total combined course score matters for your final grade!! (See the detailed grade info page for more info. In the end, it is your combined score, including homeworks and labs, that is all that matters gradewise)
- About 1/3 of the class scored above 90%, that's really fantastic, congrats!
Well over half the class scored about 80%. Rocking...
- The average on the Multiple Choice section was 10/13 questions.
- The average on the written section was 25/30 possible points. All 3 pages were (roughly) equally hard for the class (although the middle question, from the lab where we added in an extra resistor, was the hardest, with an average of 74%
The percent correct overall was just a little higher than it was for the MC section.

If you are really unhappy about your score, please read this page. It has suggestions for concrete steps you might take. Also note the "I need help" link at the left side of all our course pages. After reading these, if you'd like to come see Prof. McElroy or Prof Pollock, check out the "Help Room hours" link, or the "contacts" link, or just email us, or visit before/after class.

If, after looking over your returned exam, you feel you were misgraded on the long answer portion, take the following steps. Do not write anything new on your exam! First, look carefully at the online solutions (on D2L). Then, talk to your TA - show them what you did. They may be able to explain why we graded as we did. But if you still feel that some mistake was made, write a brief but clear note (on a SEPARATE piece of paper) and staple it to the exam. Give this to your TA, or directly to Prof. McElroy. He will look it over and decide what to do. (If you still have questions after all that, feel free to check with Prof. McElroy or Pollock in person!)

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More information about exam 1 (study guide, etc) is on this saved older page.

The class did fine on exam #1. We are very pleased with this result - we felt it was a reasonably hard test, and the class as a whole did just fine. Here is a histogram of class results on exam #1:

exam1

"Adjusted" means that we dropped everyone's lowest multiple choice question, you got a "freebie" on that exam portion. (So, the exam was therefore out of a total of 95 possible points, 5 points each for 11 MC questions, and 40 points of long answer). The Adjusted score is expressed as a percent of those 95 points.
(If you got a perfect score on the Multiple Choice, congrats! Then we didn't drop anything, and just computed your score in the usual way, out of 100 possible points)

- The average score was 73%. This is good work, the test was not easy!
- The median was just below 76% (That means half the class scored above 76%).
- The "Standard Deviation" was 15%.
- We don't assign letter grades to exams. Only your total combined course score matters for your final grade! (See the detailed grade info page for more info)
- About 1/5 of the class scored above 87%, that's really fantastic, congrats!
- The average on the Multiple Choice section was 7.9/12 questions (but in the end, we dropped one missed one)
- The average on the written section was 30/40 possible points. All 4 pages were (roughly) equally hard for the class (page 1 was just a little higher scoring on average), and the percent correct overall was just a little higher than it was for the MC section.

If you are really unhappy about your score, please read this page. It has suggestions for concrete steps you might take. Also note the "I need help" link at the left side of all our course pages. After reading these, if you'd like to come see Prof. McElroy or Prof Pollock, check out the "Help Room hours" link, or the "contacts" link, or just email us, or visit before/after class.

If, after looking over your returned exam, you feel you were misgraded on the long answer portion, take the following steps. Do not write anything new on your exam! First, look carefully at the online solutions (on D2L). Then, talk to your TA - show them what you did. They may be able to explain why we graded as we did. But if you still feel that some mistake was made, write a brief but clear note (on a SEPARATE piece of paper) and staple it to the exam. Give this to your TA, or directly to Prof. McElroy. He will look it over and decide what to do. (If you still have questions after all that, feel free to check with Prof. McElroy or Pollock in person!)