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Homework Help: Proton Beam therapy (magnetic field)

  1. Oct 28, 2008 #1
    1. The problem statement, all variables and given/known data
    A beam of protons with v=1.8x10^8 are deflected 90 degrees by a constant magnetic field. The trajectory of the beam has a circular arc with a radius of 4m.

    I am asked to find the magnitude of the constant magnetic field.

    2. Relevant equations

    I know that r=mv/eB. When solving for B the equation is B=mv/er. Right?

    3. The attempt at a solution

    This gives me 7.515 for the magnitude of the magnetic field. The correct answer is 0.47T.
    Did I start with the wrong equation?
  2. jcsd
  3. Oct 28, 2008 #2


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    Welcome to PF.

    You may have entered a number wrong. Using your values I get 0.47T as well.
  4. Oct 28, 2008 #3
    Ahh... I see.

    That was easy. Thanks!
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