Recent content by tstin

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    Derivation of current density in quantum mechanics

    If z is a complex number, then z=z_{1}+iz_{2} and its complex conjugate is z^*=z_{1}-iz_{2} Then it is easy to prove z+z^*=z_{1}+iz_{2}+z_{1}-iz_{2}=2z_{1} and from this is is obvious that z_{1}=\mbox{Re}\left(z\right)=\frac{z+z^*}{2} Similarly, z_{2}=\mbox{Im}\left(z\right)=\frac{z-z^*}{2}...
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    Expressing cartesian unit vectors in terms of spherical unit vectors

    That's right... essentially, what I described above is the same as calculating the Jacobian, which is the matrix given by TAMEPLAH. A more rigorous description of coordinate transformations would involve a discussion of Jacobians and why they work and stuff... that's for whoever's feeling...
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    Angular momentum of a charged insulator ring in a decreasing magnetic field

    This is wrong, of course. There's no nice Gaussian surface one can draw to calculate the electric field due to a ring of charge. We can only analytically calculate the field along the ring's axis. Here's an http://www.physics.buffalo.edu/~sen/documents/field_by_charged_ring.pdf" trying to...
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    Angular momentum of a charged insulator ring in a decreasing magnetic field

    This was an old qual problem I was just looking at. Let me describe how to solve it, and then ask another question I had that my solution doesn't answer. According to Lenz's Law, (or really to Maxwell's equation \vec{\nabla} \text{x} \vec{E} = -\frac{\partial{\vec{B}}}{\partial{t}}), the...
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    Expressing cartesian unit vectors in terms of spherical unit vectors

    Thanks for the LaTeX help, but note that the r's cancel in the \hat{\theta} component of the final solution because the \hat{\theta} component of the gradient in spehrical coordinates has a 1/r in it already. So the last line should read \nabla z = cos(\theta) \hat{r} - sin(\theta)...
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    Expressing cartesian unit vectors in terms of spherical unit vectors

    This is a problem I have seen a lot on the internet, and no one seems to know what the asker is talking about. We want to know how to express the CARTESIAN unit vectors \hat{x}, \hat{y}, \hat{z} in terms of the spherical coordinates r, \theta, and \phi and their respective unit vectors. The...
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