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Mangnetic Force

  1. Sep 12, 2009 #1
    1. The problem statement, all variables and given/known data

    An alpha particle is moving at constant speed in a circle, perpendicular to a uniform magnetic field, making a revolution every 60 nanoseconds.
    Its speed is non-relativistic

    What is the numerical magnitude of the magnetic field in T ?


    2. Relevant equations
    alpha particle (2 protons + 2 neutrons)

    We have here T= 2(pi)m / qB

    in which
    m=Mass (alpha particle= 6.64*10^-27) kg
    q=Charge = 2(1.6*10^-19) C
    T= (60*10^-9) s

    3. The attempt at a solution

    This should be just plugging in, I got 2.1729, yet it is wrong...
    Why?
     
  2. jcsd
  3. Sep 12, 2009 #2

    rl.bhat

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    What is the radius of the circle?
     
  4. Sep 12, 2009 #3
    it is not given....

    I dont think we need it to solve the question
    The formula of it doesn't involve any radius....
     
  5. Sep 12, 2009 #4

    rl.bhat

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    When the alpha particle is moving ina circle, what is the force acting on it?
    What is the force on alpha particle due to the magnetic field?
     
  6. Sep 12, 2009 #5
    The Centripetal force is going to equal the magnetic force.

    Note that w = v/r

    Centripetal force , F=m v^2 /r..
    =m r w^2

    And the magnetic force on the alpha particle is, F = B q v
    = B q w r

    m r w^2 = B q w r
    m w = B q

    in which w= 2(pi) / T

    Thus T= 2(pi)m / qB
     
  7. Sep 12, 2009 #6

    rl.bhat

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    Your answer appears to be correct.
     
  8. Sep 12, 2009 #7
    Thanks, the problem might be those constant...

    Side Note: I just realize I got a typo on the topic... crap
     
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