# Search results

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...
16. ### Gauss' law help please.

Ya, I figured it out it just took me a while to remember all the stuff I learned last year. It wasn't that I thought what you had wasn't Gauss' law, I just wasn't sure how to put it into the form I needed. Thanks for the help.
17. ### Gauss' law help please.

Thanks, but I think I need to do it a different way. We are using Gauss' law in its basic form of \int\int_s E . n ds=\frac{q}{\epsilon} I guess I am confused because for a infinite thin sheet you get \frac{\sigma}{2 \epsilon} and it would seem outside of the slab this is what the field would...
18. ### Gauss' law help please.

For this problem I am giving the following: An infinite slab of charge parallel to the yz plane whose density is given by: p(x)= t, -b<x<b; 0, |x|>b; Where t and b are constants. And I am to find the electric field. I am pretty confused on how to do this problem. I know that the...
19. ### Surface integrals (without real integration)

I think i'm just confusing myself more :uhh: If I integrate that vector function around a cylinder than it will be 0. I can imagine that we would have constant vectors of magnitude Ln[r^2] all in the radial direction around the cylinder for any z value. I guess I still don't have a good enough...
20. ### Surface integrals (without real integration)

Given F= (ix+jy) Ln(x^2+y^2) and given S, which is a cylinder of radius r, and height h(in the z axis) evaluate \int\int_s F.n \,ds. It says that you shouldn't need to do any work if you think about it enough. I figured I could find the area of the main part to be 2 \pi r h then multiply that...
21. ### Simple question out of div,grad,curl & all that

I am going through the first chapter of div,grad,curl and all that and am a bit confused about problem 6. The question is: Show that the field lines y=y(x) of a vector function F(x,y)=F_x(x,y)i+F_y(x,y)j are solutions of the differential equation \frac{dy} {dx} = \frac{F_y(x,y)} {F_x(x,y)} I...
22. ### Easy and quick Special Relativity before my exam

Well I am having my exam tomorrow over special and very basic general relativity. I have one area I am still a bit fuzzy on now that I look back at our last exam. I am confused on when you can use just Lorenz time dilation/length contraction to when you need to use the full Lorenz...
23. ### Relativistic momentum

Thanks, the book does it similar to how you solve it, but I like to be able to solve things in a way that I will remember on a test just in case I can't find the easy way. Thanks, I figured it was something stupid like that.
24. ### Relativistic momentum

I am having trouble with getting the right answer for this problem that is pretty simple and it is driving me insane. You start out with a pion that decays into 2 photons that split at an angle theta in opposite directions from the original pion. The velocity v of the pion is 2.977*10^8 m/s...
25. ### A few special relativity questions before my exam

Ok so my exam is here tomorrow and I don't feel like I have the grasp on SR I would like to have, most of the books I ordered recently got here so I haven't had time to read them yet. So if I could get any help with some questions I would really appreciate it. 1.) When using the general...
26. ### Linearizing a function

Thanks, just incase anyone is wondering it is a special case(should have said that) so it doesn't have the square root.
27. ### Linearizing a function

Well this is a physics related question but I think putting it in math is best. I am trying to linearize the doppler shift function of light. I know that means to expand it and take the linear terms but don't really know what to do. I was guessing a taylor series expansion but...
28. ### Easy special relativity

Thanks for the help, it's starting to come together now.
29. ### Easy special relativity

Thanks for the help, I see the above part is right with length contraction. the part I dont get I guess is why it doesn't work with time dilation also. If we have: t' = 7 years(the time measured on the craft) t = 12 light years/v = the time it takes the ship to get to planet X from earths time...
30. ### Easy special relativity

Easy special relativity :( I have this problem with special relativity, its really confusing for me ;) I have this problem that seems very easy but I am of course not getting the right answer. A planet X is 12 light years away as measured from earth. If a rocket leaves from earth and flys to...