## Thursday, August 26, 2010

### PH253: HW1, redux; notes on radiation

First, I've heavily updated the notes on radiation, the current version has the same URL. We'll start off by considering the E and B fields for observers in motion relative to the source, and work our way up to accelerating charges and radiation. Again, not all the sections in the notes will be covered (those with a * are considered optional), I was just trying to be thorough.*

Second, I realized I forgot to give any hints on HW1 problems 5b,c and 10. I'll leave some time tomorrow for going over 5b,c and other questions you have, and 10 we will do in the course of the lecture. Note that for 5b velocity is the integral of acceleration through time. Set that up and realize it is separable (manipulate the du and dt's like fractions), and Wolfram knows the integral. For 5c, integrate once more, position is the integral of velocity through time. Problem 10 we're going to do in class as part of Thursday's lecture.

* The main idea is: relativity -> field of a charge in motion -> charges that start or stop -> accelerating charges -> radiated power. Then, power -> radiation reaction force -> harmonic oscillating charge with damping and driving field -> radiation power of a charge exposed to a driving field. Last, relate radiated power to the energy density of the thermally-generated field oscillating charges bathe at temperature T in to get Rayleigh-Jeans, and add Planck's hypotheses to fix it. It will all make sense in time ...