Search results

  1. O

    Dimensions of intensity

    Homework Statement I know that intensity is power per unit area. When I do a dimensional analysis, it reduces down to mass per cubic time. Is there any physical significance to that? Homework Equations I=P/A The Attempt at a Solution
  2. O

    MATLAB Indicate mean with a bar in Matlab

    I want to put the following as an axis label on a plot, but I cannot figure out how to get the bar on top in Matlab \bar \xi Thanks.
  3. O

    Why is diffusion coefficient = 1/2?

    Homework Statement I'm working with a 0ne-dimensional random walk and looking at Fick's second law, below. All I've read seems to take D = 1/2 as a given for ordinary diffusion, but where does this come from? Is there a way to derive it? Homework Equations \frac{\partial } {{\partial...
  4. O

    Function works on Windows but not Linux

    I downloaded largestcomponent.m today and it runs fine on my PC (Win 7 Enterprise SP 1) but when I try it on my Linux machine (Ubuntu 10.04 LTS) I get this message: ??? Undefined function or method 'largestcomponent' for input arguments of type 'double'. Even if I put the function file in...
  5. O

    MATLAB Matlab Legend Problem

    I am trying to make a plot of four pairs of time series. The plot appears fine; I have two lines in each color as I want. The problem, in this case, is that the first two legend items both have red lines, and the second two both have black lines. I want each legend entry to match the color of...
  6. O

    Ordinary Diffusion and integration by parts

    Homework Statement For ordinary 1D diffusion show that the mean value of the square of the position is equal to 2Dt Homework Equations \left\langle {x^2 \left( t \right)} \right\rangle \equiv \int\limits_0^\infty {x^2 p\left( {x,t} \right)dx} \frac{\partial }{{\partial t}}p\left(...
  7. O

    Discrete power law distributions

    I'm not a mathematician, but I want to understand how a mathematician would view this issue. I'm working primarily with degree distributions for finite graphs, and when I make a log log plot of the frequency distribution the data points form a nice straight line (at least for low degree...
  8. O

    MATLAB Questions about plotyy in Matlab

    Here is the relevant piece of code as it stands now: figure(2) [AX,H1,H2] = plotyy(plot2data(:,1),plot2data(:,2),plot2data(:,1),... plot2data(:,3)); set(get(AX(1),'Ylabel'),'String','Mean Value of C_{a}','Color','k') set(get(AX(2),'Ylabel'),'String','Mean Value of C_{b}','Color','k')...
  9. O

    Goodness of fit question

    I am familiar with linear regression and the correlation coefficient. My current problem involves a data set that is pretty linear on a log-log plot. I have calculated the slope by taking logs of all my x's and y's, and doing the linear regression on the transformed data set. The resulting...
  10. O

    What is the significance of Fermi Temperature?

    Homework Statement What is the significance of Fermi Temperature? Homework Equations I know it is the ratio of the Fermi energy (or the chemical potential at the Fermi energy) to the Boltzmann constant. The Attempt at a Solution What does it MEAN? I've worked out the Fermi...
  11. O

    LaTeX LaTex Problem

    I hope you can help me with this problem. A few days ago, I began a post with a LaTex equation in it, but never completed the post (I got the answer I needed). I'm trying a new post today, and no matter how or what I enter as LaTex, when I preview the post I see the equation I tried to use a...
  12. O

    Question on tensor notation

    Homework Statement Not a specific problem; I'm trying to understand what the notation means; I'm using primarily Griffiths, Marion and Jackson textbooks. The notation for a matrix, with the superscript row index and subscript column index I understand. For the EM field tensor, Griffiths...
  13. O

    Hertz's measurement of c

    I would like to find a device to reproduce Hertz's experiment that demonstrated the transmission and reception of EM radiation. The equipment as I recall used a Leydan jar, an inductance coil to boost the voltage, a capacitor with a gap that sparked, and separately a ring with a small (I...
  14. O

    Hypersphere Volume - Fractional Dimensions

    Homework Statement I've completed the derivation of the hypersphere volume for integer dimensions, and my solution matches what's on Wikipedia. How can I generalize it to fractional dimensions? Homework Equations The Attempt at a Solution Not a clue; my only guess at this point...
  15. O

    MATLAB Matlab save/load question

    I have calculated a variable called FNET. I have saved FNET to the hard drive using the following command: save(fullfile(BasePath,'FNET'),'FNET','-mat') BasePath is a string that gets the file to the correct directory on my hard drive. First Question: FNET shows up in the correct...
  16. O

    Understanding Jackson (again!)

    Homework Statement Jackson Section 5.10, the uniformly magnetized sphere, I'm trying to fill in the steps from his first equation to Equation 5.104. I get the same potential except I am lacking the cos\theta term. My work shown below. Homework Equations The Attempt at a Solution...
  17. O

    What does nonpermeable mean?

    Homework Statement I'm reading Jackson Section 5.10, where he solves for a uniformly magnetized sphere "embedded in a nonpermeable medium." I'm not looking for an example, but to understand what it means. It can't mean there is no B or H field external to the sphere; in fact, Jackson has a...
  18. O

    Magnetism Proof

    Homework Statement Prove \int\textbf{B}\cdot\textbf{H}d^{3}x=0. There is no current density. Homework Equations The Attempt at a SolutionThrough a vector identity and the divergence theorem, I get \oint\Phi_{M}\textbf{B}\cdot{d}\textbf{a} but don't know how to proceed. This...
  19. O

    MATLAB Matlab question

    I need program code that will extract part of a text string. For example, I have the following text string: '10-Nov-2009_0.91304_Network_N=100_k=6_p=0.02_COMM_NETWORK' and I want to wirte code that will result in a command N=100 (ie, assigning a variable N the value of 100). I have figured...
  20. O

    Schools Picking a college for a physics major

    My son is thinking of majoring in Physics, but I've had virtually no luck in finding any information about the quality of undergrad Physics programs. Is there any objective rankings or assessments out there? Any other suggestions on how to pick would be appreciated. His interest (at least...
  21. O

    Understanding Jackson - calculation of coefficients

    Homework Statement After demonstrating that a set of functions are orthogonal and complete, Jackson presents equations like the ones shown below. I've used the equations for the Legendre series representation as an example, but he does almost the exact same thing with the Bessel functions...
  22. O

    Jackson 3.9 - my coefficients are vanishing!

    Homework Statement A hollow right circular cylinder of radius b has its axis coincident with the z axis and its ends at z=0 and z=L. the potential on the end faces is zero, while the potential on the cylindrical surface is given as V(\varphi,z ). Using the appropriate separation of variables...
  23. O

    Filling in some steps in Jackson

    Homework Statement If you have a copy of Jackson handy, this is in the middle of Section 1.7 (p.35 in my book). I'm trying to understand how he gets from Equation 1.30 to the next step (which is an unnumbered equation). Specifically, how is the term in square brackets a Taylor expansion of...
  24. O

    Electric Field inside uniformly charged dielectric sphere

    Homework Statement Either Coulomb's Law or Gauss' Law and r>R, I get \textbf{E}=k\frac{Q}{r^{2}}\textbf{r}. Q is the total charge. If R is the radius of the sphere, shouldn't the field at a point a<R simply be k\frac{Qa}{R^{3}}? Inother words, the field is proportional to the enclosed...
  25. O

    Potential for infinite line charge

    Homework Statement Find the potential a distance z from an infinite straight wire with uniform linear charge distribution. Homework Equations \int\textbf{E}\cdot\text{d}\textbf{l} The Attempt at a Solution The direction of the field is clearly radial from the wire, and dl is in...
  26. O

    Scattering Cross-section questions

    Homework Statement Problems are Shankar 19.3.2 and 19.3.3 with spherically symmetric potentials V(r)=-V_{0}(r_{0}-r)\theta and V(r)=V_{0}exp(-r_{2}/r^{0}_{2}^{}) Homework Equations f\left( \theta \right) = - \frac{{2\mu }}{{\hbar ^2 }}\int\limits_{r_0 }^r {\frac{{\sin qr'}}{q}V\left(...
  27. O

    QM Variation Method

    Homework Statement Show that variation principle (parameters ci) leads to equations \sum\limits_{i = 1}^n {\left\langle i \right|H\left| j \right\rangle c_j = Ec_i {\rm{ where }}} \left\langle j \right|H\left| i \right\rangle = \int {d\textbf{r}^3 \chi _j^* \left( \textbf{r} \right)\left(...
  28. O

    Question on perturbations

    Homework Statement Not a specific problem, but a question Homework Equations The Attempt at a Solution Is an infinitesmal rotation an example of a perturbation (in the position coordinate)? If not, what is the difference? What I'm seeing makes perturbations look like...
  29. O

    Show operator is diag in second basis

    Homework Statement Show explicitly using Pauli matrices that the S2 operator is diagonal in the second basis. Homework Equations S2=S^{2}_{1}+S^{2}_{2}+2S_{1}S_{2} 3. The Attempt at a Solution [/b] In the last term, 1 and 2 are supposed to be subscripts, and the two S's should be...
  30. O

    Matrix/eigenvalue proof

    Homework Statement Given a matrix with eigenvalues \lambda_{i}, show that if the inverse of the matrix exists, its eigenvalues are \frac{1}{\lambda}. Homework Equations The Attempt at a Solution This shouldn't be so hard. I've come up with a few trivial examples, but I would like...
Top