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

    I 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}...
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