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Homework Help: Magnetic field changing speed of particle?

  1. Aug 6, 2011 #1
    From my textbook:
    The example seems to contradict what is said above. The electron is accelerated in the negative z direction, so the velocity now has both an x-component and a z-component so the speed DOES change (magnitude larger)?
    Last edited: Aug 6, 2011
  2. jcsd
  3. Aug 6, 2011 #2
    Since the acceleration/Force is always perpendicular to the direction of motion of the electron only the velocity is changed not the speed. The electron does not gain any KE since W=Fdcos(theta) and theta in this case is pi/2.
  4. Aug 6, 2011 #3
    got it thanks!
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