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I'm a physics grad student just trying to figure out all this stuff like everyone else.
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Apr 9 |
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Capacitors and resistor in series and in parallel Is your question the HW question itself, or is there another set of questions you are just trying to get to after you straighten this out? Like Zetta said, none of these are in series or parallel. However, that doesn't mean you can't say anything about the current in the circuit. |
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Apr 8 |
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Tension $T$ in cable @user22922 No shame in being new. Jerry is indicating you will probably get a lot more help/responses from people if you include your attempt or reduce it to a conceptual question. |
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Apr 8 |
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Different approaches to calculating the Christoffel symbols @Gene - no problem. I am pretty sure I lost an afternoon of my life to these factors of 2 at one point, so I am happy to help. |
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Apr 8 |
answered | Different approaches to calculating the Christoffel symbols |
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Apr 5 |
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Quantum Electrodynamics Related: math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html |
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Apr 5 |
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A ring placed along $y^2 + z^2 = 4$, $x = 0$ carries a uniform charge of $5 \mu\ C/m$. Find $D$ at $P(3,0,0)$ The vector $\mathbf{r}$ that appears in Coloumb's law for a point for a point charge, points from the charge that generates the electric field to the point where you want to find the electric field. For the case you are considering, $\mathbf{r}$ points from the charge $dQ$ to the point $(3,0,0)$. |
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Apr 4 |
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exercise books for Feynman diagrams I am a little confused by what you mean when you say you know QFT but still need practice with Feynman diagrams. I would suggest just trying to work out the examples in textbooks like Scrednicki and Peskin, if you haven't already. Also you can peruse the web for classes people have taught where HW exercises and solutions have been posted. Better yet, just get involved with some research and you will learn what you need to know. |
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Apr 4 |
answered | Pauli matrices and the Levi-Civita symbol |
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Apr 4 |
awarded | Nice Question |
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Apr 3 |
answered | Density operator in second quantization |
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Apr 1 |
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B-field and Magnetic forces, speed of a particle Hint: Biot-Savart Law tells you how a moving charge creates a magnetic field. You need to find an equation that given a magnetic field, creates a force on a moving charged particle. The magnetic field in your problem is created by some other moving charges 'off stage'. |
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Mar 30 |
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Is Feynman's explanation of how the moon stays in orbit wrong? Strap the penny to a brick of C4. But carefully so that the penny only gets a horizontal velocity when you blow up the C4. In principle the penny can certainly escape the earth even though you are only giving it an horizontal velocity. Does this make anymore sense? |
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Mar 30 |
answered | Is Feynman's explanation of how the moon stays in orbit wrong? |
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Mar 29 |
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Calculate Capacitance in Series AC Circuits? You are trying to calculate the capacitance of an unknown resistor? I think you mistyped? |
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Mar 29 |
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Finite square well Pretty much. You can go a step further and actually try integrating $\int_{-L/2}^\infty \ dx \ e^{\kappa x}$ and you will see that you will get $ \infty$, so there isn't any hope of normalizing this to anything finite. |
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Mar 29 |
answered | Finite square well |
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Mar 28 |
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Lorenz gauge fixing The fact that we can write down equations like this at all is because of the gauge redundancy of fields like $A^\mu$. That is, there is extra freedom in these variables as opposed to just writing things in terms of the electric and magnetic fields $\mathbf{E}$ and $\mathbf{B}$. If we choose to eliminate some of this redundancy is our choice, or the `gauge' we choose. This is, for an equation like the one you wrote above you are choosing to restrict the extra degrees of freedom in some way. Choosing a particule $\psi$ is part of this choice. |
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Mar 28 |
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Lorenz gauge fixing Gauge conditions are a constraint we choose to impose. That is, we don't solve gauge conditions for unknowns, we impose gauge conditions. |
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Mar 25 |
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Regulator-scheme-independence in QFT (2) I am not sure if things give the same results independent of scheme, but perhaps in the IR they will. The fact that when you look in the PDG they tell you 'we used MS bar here' indicates it matters what scheme you use. But I have never properly understood this. |
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Mar 25 |
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Regulator-scheme-independence in QFT This is murky water for me for indeed, so take everything I say with a grain of salt. I think there are 2 separate issues going on. (1) Whether the physics quantities are regulator independent. Like I said before, to my knowledge this is the content of the CS equation - we literally a physical quantity that we can measure and take a derivative with respect to mu and say this has got to be zero. |
