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Homework Help: Electrons in a magnetic/electric field

  1. Jan 12, 2013 #1
    How could you tell whether moving electrons in a certain region of space are being deflected by an electric field or by a magnetic field (or both)?

    The answer from the text book is:
    If the moving electrons are changing speed as they are being deflected, then an electric field is present. This will be the case whether or not a magnetic field exists in the same region of space. If the moving electrons are being deflected but they are not changing speed, then only a magnetic field is present.

    I don't understand this explanation, why would the speed only change in an electric field, but not in a magnetic field?

    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jan 12, 2013 #2


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    Staff: Mentor

    Consider, separately, how the magnetic and electric forces are applied to the electron. What directions do they act? What do the resulting trajectories look like?
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