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Magnitude of a field

  1. Feb 23, 2010 #1
    At the fermilab accelerator in Batavia, Illinois, protons having momentum 4.8 x 10^-16 kg x m/s are held in a circular orbit of radius 1 km by an upward magnetic field. What is the magnitued of this field?

    r = 1000 m

    So i do not understand what are we trying to find here? the question asks for the magnitude of the field, but how are we to solve for the magnitude with just 2 varibale given to us? Very Confuzed
  2. jcsd
  3. Feb 23, 2010 #2


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    Hi dev-hud! :smile:

    Do it systematically, one step at a time:

    i] what is the force of a field B on the proton?

    ii] what force is necessary to make the proton move in a circle of radius r?
    (call the mass m, and the velocity v)
  4. Dec 5, 2010 #3

    since p=mv therefore: B=p/qr
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