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Hamiltonian for a free electron in electromagnetic field

  1. May 17, 2015 #1
    hello, how to derive the hamiltonian for a free electron in electromagnetic field mathematically ?
    for a first step what is the lagrangian for a free electron in the EM field in classical mechanics ?
    the physics text book always like to give the results directly.
     
  2. jcsd
  3. May 17, 2015 #2

    blue_leaf77

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  4. May 18, 2015 #3
    thanks, I understand how to derive the Hamiltonian from Lagrangian.,
    however, the file gives the Lagrangian directly without any reason.
     
  5. May 18, 2015 #4

    blue_leaf77

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    Up to now, all literatures I have read always deduce the Lagrangian from the equation of motion (Lorentz force law) by, apparently, inspection - kind of trying to seek for the right form of L and check it by plugging it into the equation of motion of L. I have never seen a reference doing the reverse way, that is deriving the Lagrangian from the energies like we usually do in systems involving gravitational potential only. Perhaps there are such references but I just never come across them. Anyway, just for a check you can plug in the final form of the Lagrangian you found there into the Lagrange-Euler equation (the equation of motion), I think you should end up with the expression of Lorenty force.
     
  6. May 18, 2015 #5
    yes, I put the L into the E-L equation, could derive the Newton's equaiton of motion. But I think it is very smart to work out the lagrangian.
     
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