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Proton in a magnetic field

  1. Apr 21, 2008 #1
    1. The problem statement, all variables and given/known data

    I have a circular magnetic field and a proton (A) a distance Ra from the center of the circle. The magnetic field is traveling into the page and is decreasing at some rate B(t). I have the radius of the circle Rb.

    The question is that when the proton is released, what happens to the proton?

    2. Relevant equations

    F = qv x b
    Right Hand Rule

    3. The attempt at a solution

    I'm pretty sure that with a changing magnetic field, it will create an induced current/magnetic field that will exert a force on it. Its not a mathematical problem necessarily i just need to know what happens to the proton. in the midst of a changing magnetic field.
     
  2. jcsd
  3. Apr 21, 2008 #2
    is the proton moving?
     
  4. Apr 21, 2008 #3
    well i assume it starts as stationary because the problems says "when the proton is released". so no i dont think theres a velocity vector to it.
     
  5. Apr 21, 2008 #4

    Doc Al

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    Staff: Mentor

    The changing magnetic field will create an electric field (induced EMF).
     
  6. Apr 21, 2008 #5
    so the induced EMF (E) will exert a force on the proton F=qE then?

    So... i use faraday's law to determine the E and just multiply it by q?
     
  7. Apr 21, 2008 #6

    Doc Al

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    Staff: Mentor

    Right. But as soon as it starts moving there will be a magnetic force on the proton as well.
     
  8. Apr 21, 2008 #7
    so at the end of the day.

    the induced emf (the E field) will exert a force on the proton, but as the proton moves, there will be a magnetic force on the proton (cross product of its velocity and the magnetic field)?

    in terms of vectors then...can i expect it to move wherever the resultant of the summed E and B field vector?
     
  9. Apr 21, 2008 #8

    Doc Al

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    Staff: Mentor

    Sounds good.

    You can expect that the net force on it will be the vector sum of the electric and magnetic forces.
     
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