# 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?

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...
3. ### 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...
4. ### 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...
5. ### 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...
6. ### 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...
7. ### 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...
8. ### 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...
9. ### 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...
10. ### 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...
11. ### 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...
12. ### 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...
13. ### 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...
14. ### 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...
15. ### 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...
16. ### 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...
17. ### 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...
18. ### Becoming a professor?

I have always had the idea of becoming a physics professor after I graduate and go to graduate school, but the more I hear about it the more weary I am of this happening. I go to University of Cincinnati which isn't really known for its physics or anything but see that all of the professors went...
19. ### Need help with wave motion quickly please

Well I am having some serious troubles with chapter 6 from French's book on vibrations and waves. Here are the things I am having trouble with. 1. Show that for a vibration of an air column an open end represents a condition of zero pressure change during oscillation and hence a place of...
20. ### Coupled oscillator problem

I am given a set up with two pendulums of unknown mass m, of length =.4 meters. They are connected together with a spring of unknown spring constant k. It says when one of the bobs if fixed in place the other has a period of 1.25 seconds. I am then asked to find the period of each normal mode...
21. ### Average potential and kinetic energy of SHO

I am using Frenches book on waves and have a question. You have a standard driven damped oscillator and I am suppose to find the average potential and kinetic energy of it. They are both similar so I will just use the potential for example. I took \frac{1}{T}\int^T_0 \frac{1}{2}KX^2 dt Where...
22. ### Complex exponential help please

Express the following in the form z=Re[Ae^{i(\omega t+\alpha)}] z=cos(\omega t - \frac{\pi}{3}) - cos (\omega t) and z=sin(\omega t) - 2cos(\omega t - \frac{\pi}{4}) + cos(\omega t) I got a few of the problems correct by using trig. identities but it was pretty tough and two I can't get...
23. ### Relativity and gravitons?

I am doing some research this summer with a professor and we are learning GR. For the first time I am thinking about gravity actually in terms of geometry and started to ask my professor questions. He is a VERY smart man but I didn't get exactly what I was looking for with one question. I asked...
24. ### Basic GR math question about dimensions

Ok, this is a really stupid question but it is something that is really confusing me. I am confused on the concepts of dimensions, for example of a sphere and how they relate to Euclidean geometry. A sphere in 2 dimensions using Euclidean 3 dimensional geometry doesn't really make too much sence...
25. ### Simple volume help please

Ok,so I have a simple volume problem that i'm having a little trouble with. I want to rotate the region in the first quadrant bounded by the following formulas around the Y axis. y=x^3 y=2x-x^2 I solved for x and got x=\sqrt[3]{y} x=1- \sqrt{1-y} I know I get two roots but I am...
26. ### Studying Intermediate books?

What are good intermediate/higher level college physics books are out there for Mechanics and electrodynamics? I am a physics major in an introductory calculus based honors physics class right now(we are using the Serway and jewett text) and want to get a jump start on physics for next year. I...
27. ### Calc two help please

Calc two help please :( Ok, I have the following two problems: \frac{d}{dx} \ \int_0^1 \ e^{tan^-1(t)} \ dt \\\\ and \int \ \frac{Sin[x]}{1+x^2} \ dx I have tried to do substitution on both and integration by parts on the second one but nothing seems to work. If I could...
28. ### Standard Deviation?

Well in physics lab we just did a lab where we calculated the acceleration do to gravity,this didn't include the air resistance, so the ligther stuff shouldn't be perfect. We took video of stuff falling and then put the data from that into mathematica and fitted a quadratic equation to it and...
29. ### Why can't I find a good book?

Are there any good mechanics books out there for a first year physics student? My text book(serway physics for engineers and scientists) is ok but a bit lacking in some places. I have bought alot of books but it seems they either fall into one of two categories. They either are all problems with...
30. ### Need help with friction forces please!

Hi, I was giving a problem by my teacher that will most likely be on the exam. A block, m1, is ontop of another block, m2 and there is a constant friction, mu, between the two blocks. Between block m2 and the ground there is no friction. What is the largest force, P, that can be put on m2 and...