Notes on EM waves, radiation, etc

Here are some notes on radiation, EM waves in conductors and insulators, etc - the stuff we've been covering the last several lectures. They are rather long, and incomplete in places ... but they do cover some interesting things I didn't quite get time to go over in lecture.

The first part is deriving the radiated power by accelerating charges, and applying that to several systems (oscillating charges, circular motion, etc.). The second part is deriving the blackbody radiation, which we did not cover (you'll see this in PH253). The last part is EM waves in solids, complex conductivity and dielectric functions derived from a model of oscillating charges. An appendix shows how to derive B from E in a moving reference frame.

There will not be any further HW.

Given that next week is dead week and you have an exam on Friday, we'll call it quits at 8 homework sets. Christmas comes early this year ;-)

Exam 3

The coverage for exam 3 on Friday will be:

• magnetic fields (2 problems; Ch. 28.2-4, 6, 8-10; 29.2-6)
• motion of charges in magnetic fields
• fields due to current-carrying wires (Ampere, Biot-Savart)
• induction (2 problems; Ch. 30.2-8)
• motionally-induced voltage
• Faraday's law 
• ac circuits (1 problem; Ch. 31.2-9)
• filters
• impedance

Nothing on op-amps/transistors/comparators, Maxwell's equations, EM waves, or relativity for this exam, though some of that may show up on the final. Similar to the homework problems, but less involved. Out of the 5 problems, you will have to choose 3 to solve, so the odds are not bad. You'll have 50 minutes for the exam. I'll provide a basic formula sheet with everything you really need, and you can bring in one sheet of your own.

I'll try to provide some more details on Wednesday in class, but feel free to remind me or ask some questions. I will really try not to make it too difficult ...

New Spring courses

We have two brand-new never-before-offered courses this spring you might want to consider:

AY 155 - Life in the Universe     (Silverstone)

PH 482 / PHL 480 - Physics & Metaphysics   (LeClair / Hestevold)

Links go to course syllabi, let me know if you want any more information.

Course evaluations

It is that time again ... please remember to do your online course evaluations. I won't see them until well after final grades are due.

This course will be using an online system for collecting the end-of-semester Student Opinions of Instruction questionnaires.  Your response is very important and is used to assess curricular and instructional quality, as well as to identify opportunities for improvement.  The online system enables you to: 

• complete the questionnaire anytime, anywhere, at your own pace allowing for more thoughtful and constructive responses
• save and return later, as well as review and edit responses prior to submitting
• responses are confidential; only a summary of all student responses will be provided to your instructors and administrators.
• For more information about this process, go to http://oira.ua.edu/soi/soi_info.html.
• Beginning November 28, 2011, the Student Opinions of Instruction questionnaires will be available. You may access them as follows:
• Login to myBama and select the “Your opinions matter!” image on the Student tab.  Once in the system, you will see a list of courses you are being asked to evaluate.
• An invitation containing a link to login will be sent to your Crimson account.  Up to 3 reminders will be sent; reminders will only be sent to those who have not submitted all questionnaires for all courses.

HW8 hints

Problem 6 is a bit sneaky. Think about how the capacitance relates to the geometry of the capacitor (C ~ A/d), and how those distances are contracted. If you move toward the plates along the axis, the plate spacing is contracted, but area remains the same. If you move perpendicular to the axis, the spacing is the same, but what happens to the surface charge density?

As one hint, charge is invariant, and always the same no matter what relative motion there is.

As a stronger hint, I was about to post my notes on radiation, which starts out with the fields of moving charges ... 

For 7, note that F = qE = dp/dt, with momentum p=(gamma)mv. Then

dp/dt = (gamma) m dv/dt + mv d(gamma)/dt

With the definition of gamma, grind through the derivatives and it should work out.

I'm going to run through #6 and 7 tomorrow in class in any event, just to make sure you know how to get started.

Final project parts have mostly arrived

Most of your stuff is in, I think we're only waiting on the multiplying chip, which should arrive on Tuesday. Here are some details about what I've got ...