Physics 2020: Fall '12

General Physics 2 (Electricity & Magnetism, and Optics)

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

Exams and Grades

EXAM 2 coming up, 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.
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Second midterm is Thursday Oct 25, 7:30 - 9:15, in our regular classroom.

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 TWO SIDES (front and back) of 8.5 in. x 11 in. paper for the second 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 one, with multiple choice and long answer questions. (The number and balance of those might be slightly different, but not radically)

Physics is inherently "cumulative", so material from Exam 1 could and will certainly reappear on this test! However, the primary focus on Exam 2 is newer material covered since the first midterm, basically the latter part of Ch 17, and Ch. 18 and 19 of our text, with only a little bit on magnets (maybe a basic magnet question or two on Ch 20.1 material, basically on the "pattern" of magnetic fields around magnets, or around a long current-carrying wire, and the principle of superposition). But the main emphasis is on current, and circuits, and all the related ideas around those, as well as older (important!) stuff like voltage, E-field, and capacitance.

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

Note: we skipped Ch 18-7 and 8, and 19.6, that material will not be on the exam.

Ch 20: Not a heavy emphasis on this exam, but you should know the basic B-field pattern of a magnet (a dipole field), and the attraction/repulsion story of N- and S- poles. You should be able to superpose 2 (or more) B-fields to get the total field. You should be able to correctly predict the direction of B field around a long wire (first right hand rule).

CH 19. You should be able to use Ohm's law in a variety of circumstances, and apply the principles of conservation of charge (Kirchhoff's first law, "current in = current out of any point, in steady state") and conservation of energy (Kirchhoff's second law, "sum of Delta V = 0 around any loop) to help "solve" questions about circuits, including current through elements, voltage across elements, and power dissipated (or generated) in circuit elements (where "element" here means a battery, or a resister, or a meter).
You should understand how to include ammeters and voltmeters in simple circuits to measure current and voltage. You should be able to handle both "ideal" situations, and also real ones where circuit elements have small internal resistances.
You should be able to simplify circuits, or parts of circuits, using the ideas of parallel and series equivalent resistors. (That means recognizing when elements are in series, in parallel, or neither!)
You should be able to trace out(and label) voltages, and voltage differences, in simple circuits.
You should be able to interpret symbols and terms like "ground", EMF (a synonym for battery voltage) ", "fuse (or circuit breaker)", "variable resistor" , ammeter, and voltmeter, and be able to make sense of a picture of a "real circuit" like we might set up in our lab.

Ch 18: You should be able to distinguish voltage from current, be able to relate current to amount of charge passing, know units of all electrical quantitities we've used in class (like, Volt, Amp, Ohm, Farad, Tesla, resistivity, Watt, etc)
You should be able to relate resistance (R) to resisitivity (rho), and apply the formula for resistivity as a function of length and area.
You should be able to use and interpret Ohm's law in a variety of settings (the applications of which are most of Ch 19!)
You should be able to calculate electrical power in a variety of settings.
Note: We talked about AC in class, but did NOT worry about "RMS" or the difference between "peak" and "average" power, so those particular concepts will not be tested on the exam. (But we do expect you to have a basic qualitative sense that AC means voltage is alternating, and thus so is current. For instance, the kinds of things you did in lab the week you used the oscilloscope, relating frequency and period of an alternating voltage

And, older stuff:

CH 17: You might expect questions on how to calculate voltage (or change in voltage) in situations with uniform fields, or with multiple point charges.
You might have to interpret equipotential diagrams, and know the connection between voltage and electric fields. (E = -Delta V/delta distance)
You should be able to relate voltage differences to work done on a test charge. You should be able to use the unit of energy called the "electron volt", and in general know the units of the various quantities we compute.
There could be questions about capacitors, including what the E field looks like inside, what the voltage is like inside, and the relation between charge, voltage, and capacitance.
For midterm #2, we expect you to know what dieletrics do when you put them in a capacitor.

CH 16: You might expect questions on static electricity (including attraction and repulsion, electroscopes, insulators and conductors, polarization, and conservation of charge. You still need to be able to use Coulomb's law (qualitatively and quantitatively, including the vector nature of addition of foces. Can you superpose force vectors?), The electric field - how to calculate it, given charge sources, how to use it to figure out forces on test charges, and particularly how to draw and interpret "field line" diagrams.

In general, try to be careful about your use of the technical words we are learning: don't mix up current, voltage, charge, power, E-field, energy, capacitance... As usual, we also expect you to remember the basic laws from Phys 2010 that we have been talking about in class and using in homeworks - in particular, Newton's 3 laws, (and universal law of gravity), the work-energy principle, conservation of energy, the formulas (and basic meaning of) potential energy and kinetic energy, and the definition of work.

Review suggestions: First, do the obvious things (like doing the extra questions on the CAPA due exam day, and the lab/review problems given every week on labs, and the concept tests that I post before/after everyclass. Sometimes there are more in those files than we get to in lecture, which makes for extra practice problems)

I have two sources of "extra problems" for you that you might not be aware of. First, see the "Questions" at the end of each chapter, just BEFORE the "Problems" pages. These are quite good!! Second, check out the "Giancoli's Physics" link at the bottom left of all our course pages, he has some worthwhile sample problems (look for the more conceptual ones, that's going to be more like the style of our exam!)

For some practice questions, see the lab page - there is a sample exam available there, (here's a copy). (As for solutions - you need to figure out how to CHECK YOURSELF, not look to me to tell you if you're right or wrong. You will get feedback in your lab as well, and that's where to go to get "the answers" if you want!)

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More information about exam 1 (stuexam1dy 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:

 

"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!)