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Homework Help: Circular Motion in a Magnetic Field Problem Help

  1. Sep 15, 2005 #1
    When a particle with electric charge q moves with speed v in a plane perpendicular to a magnetic field B, there is a magnetic force at right angles to the motion with magnitude qvB, and the particle moves in a circle of radius r. This formula for the magnetic force is correct even if the speed is comparable to the speed of light. Show that p = qBr even if velocity is comparible to c. Remember that F does not equal m*a at very high speeds.

    Ive been working trying to solve this problem for several hours so I think I need some help. I've been trying to use the momentum principle, p(final) = p(initial) + F*t. Can anyone offer some help or advice?
  2. jcsd
  3. Sep 15, 2005 #2


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    Why would one use "p(final) = p(initial) + F*t."

    Think of angular momentum. If the charge does not radiate, nor collides with another particle, then it has constant angular momentum.

    When a particle moves with a relativistic velocity, what correction is applied to the mass? What about the magnetic field?

    Think about the formula for angular momentum.
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