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Homework Help: Magnetic forces and fields

  1. Sep 5, 2007 #1
    An alpha-particle is the nucleus of a helium atom; the orbiting electrons are missing. The alpha-particle contains two protons and two neutrons, and has a mass of 6.64x10^-27 kg. Suppose an alpha-particle is accelerated from rest through a potential difference and then enters a region where its velocity is perpendicular to a 0.0195 T magnetic field. With what angular speed w does the alpha-particle move on its circular path?

    B = 0.0195 T
    m = 6.64x10^-27 kg
    w = ? rad/s

    I did this:
    v = rw
    w = v/r
    r = mv/qB
    qB/m = v/r
    w = qB/m

    how ever I am stuck on what is q?
  2. jcsd
  3. Sep 5, 2007 #2


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    Homework Helper

    your work looks right to me.

    neutrons have 0 charge. protons have [tex]1.602*10^{-19}C[/tex] charge. so for your problem q is [tex]2*1.602*10^{-19}C[/tex]
  4. Sep 5, 2007 #3
    thank you! :)
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