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Homework Help: Charged Particle Moving in Magnetic Field

  1. Mar 30, 2012 #1
    An electron is accelerated through 2.4 x 105 V from rest and then enters a uniform 1.7 T magnetic field. What are the maximum and minimum values of the magnetic force this particle

    QV = 0.5mv2

    Basically, I've got a final value from the above equations, but I'm not sure how to get a maximum and minimum as the problem states. The first equation gives me a speed of 2.9*108
    and then putting that into F=QvB gives me a force of 7.89*1011N.

    Is this the maximum? Why do a maximum and minimum occur, and how do I calculate them?
  2. jcsd
  3. Mar 30, 2012 #2


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    Staff: Mentor

    Note that the problem does not state the orientation of the magnetic field or the orientation of the electron's entry with respect to that field.

    (Also, the resulting velocity of the electron as calculated by "Newtonian" formulas is awfully high -- nearly 97% of the speed of light. Is this problem from a course that "does" Relativity?)
  4. Mar 30, 2012 #3
    All your equations are good. But I'm not sure what you're asking. Also as gneill said you didn't state the orientation of the field, but I'm assuming that's your variable.

    Fb = qv CROSS B, v and B are vectors. Meaning that the least force your particle will experience due to B is when B is parallel to v, and the most is when B is perpendicular to B.

    Make sense?
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