Exam 3

Chapter 26 (Interference and Diffraction) will not be included in Exam3. Chapter 30, on nuclear physics will also not be covered.

The exam will be open book. Bring your book and any scribbled up piece of paper that you might want.

Homework problem 2

Think of a toroidal solenoid as a cylindrical solenoid wrapped back on itself. A toroid is basically a donut. If you cut it at one point and straightened it out, it would be a regular old solenoid of length l=2πr, the inductance would be L=µN^2A/l, and the energy U=(1/2)LI^2.

The figure they provide is terrible ... look at this one.

Exam 2 scores are up

Check it out on Mastering Physics.

It wasn't that bad - average of 79.3, standard deviation 8.7. I was basically happy (though all of you might not be I guess ...). Here's the distribution, the bulk of you were in the mid-C to mid-B range.

More on this during Friday's class. Above all, do not panic: we have one exam to go, and almost no one is in any sort of danger.

Labs grades were updated as well, have a look. 

Today's lab

Today, we'll do two little experiments on mirrors & snell's law, and one on lenses:

http://faculty.mint.ua.edu/~pleclair/ph102/Labs/reflection_refraction/reflection_refraction.pdf
http://faculty.mint.ua.edu/~pleclair/ph102/Labs/lenses/lenses.pdf

Even though there are three experiments, overall it is still very fast and should not take the whole period.

In other news, the tests should be graded tomorrow. I will also extend the current HW deadline since I was out, but the next one will come out tonight (due Sun).

Today

I am sorry for the last-minute notice, but there will not be a lecture today. There will be a lab at the usual time.

Lab grades

You now have many lab grades posted on Mastering Physics.

Wednesday's lab: ac circuits

Here you go.

Makeup exam questions

They are graded, and you'll get the back tomorrow. Not on Mastering yet, but hope to update that on Tues.

The 2nd exam should be graded by Thursday - I didn't get them back this evening to get started due to a mix-up, but I'll grade them as quickly as I can.

New HW out

Due Thursday at midnight, induction/ac circuits/em waves.

The next homework after that will likely be due Saturday or Sunday. 

Office move

Over the weekend, I had to move into a different office as part of some reshuffling we're doing to free up space. My new office in Gallalee is now room 323.

Old exam answers

Exam 1, summer 2009, problem 4: this was also on the summer 2008 exam 2.

Exam 2, summer 2010: only the first three problems are material related to your upcoming exam.

1. Just walk around the middle loop - that gives 12-6I=0, and determines the current in the 6Ω resistor to be 2A.

2. Use the right-hand rule to determine directions. Two of the currents give fields pointing to the lower right corner, and two of them give fields going to the lower left corner. All fields have the same magnitude (same current, same distance; watch the geometries). All but the vertical components will cancel; find those and add together. The net field is in the -y direction, and has magnitude (field of 1 wire at center)*(sin 45)*(4 wires)~5e-6T.

3. (a) into the plane. (b) set r=mv/qB equal for both particles using the known electron and proton masses. q is the same for both, and will cancel, as will B. This gives (v_e/v_p)=(m_p/m_e)~1.8e3

4. (a,b) This filter passes speech - the inductors let low frequencies through, and the capacitor shorts out any remaining high frequencies. (c) Add all inductors together, they sum to 10.26mH. The cutoff frequency is when the inductive and capacitive reactances are equal, so f=1/(2*pi*sqrt(LC))~10.6kHz

5. This is motionally-induced voltage, like the conducting bar. (a) V=Blv~2.5mV (b) Right hand rule gives the force on a positive charge toward the drivers door, so it is the positive side.

exam 2 coverage

The following sections are fair game for the exam: 19.1-8, 20.1-9, 21.1-9.

I am aware that there is no solution to summer 2010 exam 2. I will do what I can tonight.

You did not have any homework on induction (yet ...), but it is still on the exam. Check out the old hw, exams, and solved examples in the book for some practice. We will probably have time to do a few more in class tomorrow.

There is a formula sheet essentially identical to the one you will receive on the exam here.