# Recent content by mewmew

1. ### Van der waal gas in isothermal free expansion

Homework Statement A gas obeys the Van Der Waal equation of state. The gas undergoes a free expansion from volume Vi to Vf at a constant temperature T. Find the change in entropy of the gas. Homework Equations du=Tds-Pdv+mdn The Attempt at a Solution I can solve the problem assuming du= 0...
2. ### Could someone explain this solution please?

Thanks, that makes it much clearer.
3. ### Could someone explain this solution please?

http://img478.imageshack.us/img478/5606/part1bd8.jpg [Broken] http://img183.imageshack.us/img183/686/part2yu0.jpg [Broken] We got this in class from a TA and the professor is in China and not able to answer questions. I am confused by where the probability,P(N), comes from in part a. It looks...
4. ### Integrating spherical normal components

Sorry, my terminology isn't that great. Ultimately I am trying to find < n_z >, which I believe is n_z integrated over my surface, divided by the area. Also "n_z" is the unit normal vector in the z direction, I tried to do it in tex but was having problems. Since the unit vectors come out of...
5. ### Integrating spherical normal components

I am trying to integrate the the normal vector to the surface of a hemisphere but am having some trouble. I am pretty sure that the x and y components will cancel out, and that the z component in spherical coordinates is R*Cos[theta] but for some reason I am having trouble really understanding...
6. ### Hard thermo question.

Sorry, I Should have been more specific. I took a Sterling approximation of the factorials of the form Ln(x!)= x Ln(x) - x, expanded each term, substituted in n = E/epsilon and differentiated. This was messy though and I am not sure the desired method.
7. ### Hard thermo question.

Ok, I found B more or less, by taking n=E/e. My equation for T looks pretty nasty because my multiplicity from part A was relatively nasty. I am still pretty much completely stuck on how to do C though.
8. ### Hard thermo question.

Well, it's hard to me at least :frown: http://img169.imageshack.us/img169/206/questionzg0.png [Broken] We are using Schroeders book and this problem was given to us from I assume the book by Reif. We haven't seem to have gotten far enough along in Schroeders book to have gone over this though...
9. ### Proving E&M homework problems

So our latest E&M homework assignment out of griffiths has a bit of a twist. For all of the answers that we get we have to show that they seem reasonable. I know for instance with a charged solid sphere of radius R you could take R<<r where r is the distance away from the sphere and see that it...
10. ### Entropy problem(Thermo)

Here is the problem: "A careless experimenter left the valve of a tank of helium slightly open over the weekend. The gas, originally at 200 atm, slowly escaped isothermally at 20 degrees C. What change in entropy per kg of gas occured? " I am given, K, N, and Mass of helium per mole. I am...
11. ### Easy differentials question

Ok, I have having problems with the folloing: http://www.physics.uc.edu/~simpson/pics/Desktop-Images/0.jpg How exactly do I do this? I thought all I did, for example with the first du, was set up 2 integrals, one for the dx part, and one for the dy part. I then thought for (i) the dx integral...
12. ### Schools Chances of graduate school?

Thanks for the responses so far, It is interesting that my math is so low, just because calculus 1-3 and the labs are the only thing calculated into my "math" GPA. For whatever reason calculus 4, linear algebra, etc. are all calculated into my "physics" GPA and I did ok in those classes. Should...
13. ### Schools Chances of graduate school?

I will be going into my 4th year(out of 5) of my undergraduate physics degree this year and have some questions, but first my back story. I did horrible my first quarter of school, I got D's and C's in my physics and math classes so I decided to just take some gen. ed. classes, which boosted my...
14. ### Pauli matrices

Thanks, that clears it up.
15. ### Pauli matrices

Ok, I have a stupid question on pauli matrices here but it is bugging me. In a book i'm reading it gives the equation [\sigma_i , \sigma_j] = 2 I \epsilon_{i,j,k} \sigma_k , I understand how it works and everything but I do have a question, when you have k=i/j and i!=j (like 2,1,2) you get a...