Recent content by Z90E532

  1. Z90E532

    Calculating Average Energy of a quantum state

    Homework Statement Given a wave function that is the super position of the two lowest energies of a particle in an infinite square well ##\Psi = \frac{\sqrt{2}}{\sqrt{3}}\psi _1 + \frac{1}{\sqrt{3}}\psi _2##, find ##\langle E \rangle##. Homework EquationsThe Attempt at a Solution I'm not sure...
  2. Z90E532

    Proving a sequence has a lower bound

    Homework Statement Given the sequence ##\frac{1}{2}(x_n + \frac{2}{x_n})= x_{n+1}##, where ##x_1 =1##: Prove that ##x_n## is never less than ##\sqrt{2}##, then use this to prove that ##x_n - x_{n+1} \ge 0## and conclude ##\lim x_n = \sqrt{2}##. Homework EquationsThe Attempt at a Solution...
  3. Z90E532

    Current of Spinning sphere of constant voltage

    Yeah, I think I was just having a brain malfunction... it's pretty late here. I think this is the right approach: For a surface charged sphere: ##\vec{E} = \frac{R^2 \sigma}{\epsilon _{0}r^2}## then we have ##V = - \int ^{R} _{\infty} \frac{R^2 \sigma}{\epsilon _{0}r^2} dr =\frac{R^2...
  4. Z90E532

    Current of Spinning sphere of constant voltage

    I corrected my mistake I think, but I still am not sure how to find the surface charge density from only the voltage. I think my brain stopped working.
  5. Z90E532

    Current of Spinning sphere of constant voltage

    Homework Statement Find the magnetic dipole moment of a spinning sphere of voltage ##V## and radius ##R## with angular frequency ##\omega##. Homework EquationsThe Attempt at a Solution To find the dipole moment, we need to do ##I \int d \vec{a}##, which would be ##I 4 \pi R^2 \hat{r}##, but I...
  6. Z90E532

    Finding a Left Inverse for a Cylinder: Proving Injectivity of a Parametrization

    The standard one: http://mathworld.wolfram.com/LeftInverse.html I see what you're saying about ##S##, I didn't realize that at first.
  7. Z90E532

    Finding a Left Inverse for a Cylinder: Proving Injectivity of a Parametrization

    Homework Statement Let ##S ## be a cylinder defined by ##x^2 + y^2 = 1##, and given a parametrization ##f(x,y) = \left( \frac{x}{ \sqrt{x^2 + y^2}}, \frac{y}{ \sqrt{x^2 + y^2} },\ln \left(x^2+y^2\right) \right)## , where ##f: U \subset \mathbb R^2 \rightarrow \mathbb R^3 ## and ## U = \mathbb...
  8. Z90E532

    Studying Struggling with end chapter problems (Spivak)

    Well, when I say 50%, I mean I went over the parts that I thought were important. I don't feel like finding the book again, but I did the chapters on limits, continuity, differentiability, integration etc. I've studied linear algebra, so that's not really a problem. I could definitely use some...
  9. Z90E532

    Studying Struggling with end chapter problems (Spivak)

    I'm a physics student trying to get a more in-depth understanding of math. A few weeks ago, I started studying from two textbooks, Spivak's Calculus on Manifolds and Hubbard's Vector Calculus, Linear Algebra, and Differential Forms. So far, the stuff from Hubbard's text is pretty straight...
  10. Z90E532

    Undergrad Notation in Spivak's Calculus on Manifolds

    I have a question regarding the usage of notation on problem 2-11. Find ##f'(x, y)## where ## f(x,y) = \int ^{x + y} _{a} g = [h \circ (\pi _1 + \pi _2 )] (x, y)## where ##h = \int ^t _a g## and ##g : R \rightarrow R## Since no differential is given, what exactly are we integrating with...
  11. Z90E532

    Find my Mistake? (Moment of inertia)

    Sure we can get it to work with just ##dm = \frac{M}{A} dA = \frac{M}{A}R d \theta 2 \pi r##, but this contradicts what I had found for it, which was (say ##\rho = 1##)##dm = 2 \pi r dz = 2 \pi (R \cos \theta )(\frac{R d \theta}{\cos\theta})## which leads to the integral after ##r^2## is...
  12. Z90E532

    Find my Mistake? (Moment of inertia)

    I didn't but I shouldn't have to, right? It's a spherical shell of zero thickness.
  13. Z90E532

    Find my Mistake? (Moment of inertia)

    Homework Statement Find the moment of inertia of a spherical shell Homework EquationsThe Attempt at a Solution So I've been mulling over this for about two hours now and haven't figured out where I've made a mistake. Here's what I've done: I know I can do the integral by doing ##\int ^{r}...