# Homework Help: Thermodynamics and Atomic/Nuclear Physics Left to self-study. Which one first?

1. May 4, 2007

### AznBoi

I basically have Heat/Thermodynamics and Atomic Nuclear Physics left to do, which ones should I study first? I've looked at both but they both seem so hard for me to understand. I get Heat and some of PV=nRT but I don't get the Root-mean-square speed and how it's derived. I like knowing how to come up with equations because it makes me understand the variables and relationships better. Should I just start memorizing the equations instead of trying to derive them?

Also, I'm confused about photons, and I don't really get the definitions given by the book. Which one should I try to takle first and do you have any advice on how to understand it faster? Any sites help at all? Thanks.

2. May 4, 2007

### tim_lou

the root-mean-square speed can be derived from scratch by considering a particle in a box, having a particular v_x value, and then find it's rate of transfer of momentum (use a rough time-average) (it will be $\sim v_x^2$ then take the average of the rate of transfer of momentum all together, you'll get the mean of the $v_x^2$.

it is a standard derivation found in most thermal physics books by the way.

and yes, by all means, don't blindly memorize the formula; understanding the derivation is much more important.

I'm afraid that you will have to accept the existence of photon as it is. just note that it can be treated like gas molecules in air and has energy hf (the equation is pretty much fundamental I believe, you may be able to sort of reason it out using relativistic 4-vectors but I wouldn't say that it is a derivation).

as for learning thermodynamics... I don't see a good way of "learning it fast". basically the concepts are simple enough, but you'll have to get used to differential forms and Legendere transformation (spelling?). not that you need to understand the math. really deeply but a complete understanding of the motivations of derivations in thermodynamics requires a good understanding on the math subjects I mentioned. Also, reviewing partial derivatives will help.

3. May 4, 2007

### AznBoi

Oh I'm in physics B btw, with no calculus. I understand some of heat and the form transformations of solids to liquids, liquids to vapor. Which is easier, atomic/nuclear or thermo?

4. May 5, 2007

### Astronuc

Staff Emeritus
There are simple concepts in both thermodynamics and atomic/nuclear physics, but eventually to study either in depth, one needs to learn and understand calculus. Along the way, one should learn quantum mechanics and special relativity in conjunction with nuclear physics.

5. May 5, 2007

### tim_lou

oh so you are studying physics B. I suppose you want to take the AP exams. Given the little time you have before AP, it will be virtually impossible to understand thermodynamics (and I doubt the exam will assume that you know a lot). Hence it will be best to just memorize the equations and get some intuitions out of it. (you can always come back to the topics after the exam)

If you want a derivation on the root-mean-square thing, look at wikipedia.

http://en.wikipedia.org/wiki/Kinetic_theory