Recent content by lmcelroy

  1. L

    Cross Section: Quark-Gluon vs. Quark-Photon

    This isn't a homework problem. I am preparing for a particle physics exam and although I understand the theoretical side of field theory, I have little idea how to approach practical scattering questions like these. THE PROBLEM: Dark matter might be observed at the LHC with monojet and...
  2. L

    Electromagnetism problem using Gauss's Law

    Yes, the exact same method can be applied. A typical "text-book example" gives an infinitely long wire with a linear charge density λ. Just as with a cylinder a cylindrical Gaussian surface can be used for a wire (a wire in reality is really just a thin cylinder so this makes sense). For your...
  3. L

    Derivation of relativistic motion equations from action

    ^Thanks for that. An easy to follow derivation and explanation even for someone new to the calculus of variations, as myself.
  4. L

    Derivation of relativistic motion equations from action

    Anyone willing to derive the motion equations of special relativity from the SR action: S = -m0c2∫t1t21/γ dt where: m0 = rest mass γ = Lorentz factor =1/√(1-v2/c2) v is the velocity as a function of time. The full action contains terms of the vector potential and scalar potential but assume...
  5. L

    Rotation of a sphere because of its gravitational field

    There are many factors that influence the Earth's rotation, none of which is its mass. Check this out: http://en.wikipedia.org/wiki/Earth's_rotation#Origin
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    Electromagnetism - Boundary conditions for Polarization field at interface

    Ok, after obtaining a copy of Feynman's lectures and referring to Volume 2, Chapter 33-3, I think I have found a solution. Treating the boundary as a separate region (media 3 with a relative permittivity that begins at εr1 and changes continuously to εr2) then since the P field is different...
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    Electromagnetism problem using Gauss's Law

    This was obviously posted a while ago, answering may help others though so: Begin by constructing a cylindrical Gaussian surface of radius r and length l around the cylinder. Then the electric field outside of the cylinder is, by Gauss's law: \ointE.da = Q / ε0 where Q is the total...
  8. L

    Electromagnetism - Boundary conditions for Polarization field at interface

    Not actually a homework question, this is a question from a past exam paper (second year EM and optics): Homework Statement Use a Gaussian surface and Amperian loop to derive the electrostatic boundary conditions for a polarization field P at an interface between media 1 and 2 with...
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