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Homework Help: Charged Particle Motion in a Magnetic Field

  1. Apr 3, 2010 #1
    1. The problem statement, all variables and given/known data
    A proton is moving through a vertical magnetic field. The (instantaneous) velocity of the proton is 8.5x105m/s horizontally in the north direction. The (instantaneous) acceleration produced by the magnetic force is 2.90x105m/s2 in the west direction. What is the magnitude of the magnetic field?

    2. Relevant equations
    Proton Mass = 1.67x10-23 kg
    Proton Charge = +e = 1.60x10-19 C
    B = F/(qv) (I think!)

    3. The attempt at a solution
    Okay, this seems like it should be simple, but the online homework keeps saying I am wrong, so obviously I am skipping something here. First, applying Newton's second law, I found the force, F, required of the Magnetic Force to produce the acceleration (F=ma = (1.67x10-23 kg x 2.90x105 m/s2 = 4.843x10-18 N). Then, all I need to do is put this force in the equation for a charged particle in motion in a magnetic field, which I think is B=F/(qv), so I should get, B = (4.843x10-18 N)/[(1.60x10-19 C)(8.5x105m/s), which gives me B = 3.561x10-5 Tesla.

    But apparently that is wrong. Am I missing something small, like a number, or do I have the wrong equation?

    Last edited: Apr 3, 2010
  2. jcsd
  3. Apr 3, 2010 #2


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    Science Advisor

    You have the proton mass wrong. The mass is 1.67E-27 kg.
  4. Apr 3, 2010 #3
    Ah, thanks! Indeed I do.

    And that was off of an equation/constant sheet my professor gave me!

    Thanks again, I knew it was something like that.
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