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Electron Radius in a Bending Magnet

  1. Sep 9, 2012 #1
    Problem:

    15 MeV electrons enter a bending magnet with a magnetic field of .7 tesla. What is the radius of the path of electrons?

    Equation:

    r = mV/Bq

    B = .7 tesla
    q = 1.6 x 10^-19 C

    My problem here is that I don't know how to find the velocity of the electron for this equation. The supposed answer to the problem is 7.4 cm = r, but I'm just not getting that.
     
  2. jcsd
  3. Sep 9, 2012 #2

    vela

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    With an energy of 15 MeV, the electrons are clearly relativistic. The formula you're using is only valid in the non-relativistic regime.
     
  4. Sep 9, 2012 #3
    Do you know which equation I should be using then? This problem has been stumping me for days.

    Thanks!
     
  5. Sep 9, 2012 #4

    vela

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    That's something you should be able to derive on your own or at least find on your own in your textbook or notes.
     
  6. Sep 9, 2012 #5
    I was told to use the equation above by my professor. That's why I'm confused now.
     
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