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Homework Help: Magnitude and Direction of Magnetic Field

  1. Apr 5, 2010 #1
    1. The problem statement, all variables and given/known data
    An electron experiences the greatest force as it travels 2.9 x 10^6 ms in a magnetic field when it is moving northward. The force is upward and of magnitude 7.2 x 10^-13 N. What are the magnitude and direction of the magnetic field?

    2. Relevant equations

    3. The attempt at a solution
    I don't even know how to get a diagram going for this. Anything would be helpful. Thank you.
  2. jcsd
  3. Apr 5, 2010 #2


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    What is the force exerted by a magnetic field of strength B, on a charge Q, moving at a velocity v?


    When you get that it becomes simple algebra.

    If the electron is moving northwards, what direction should the field be pointing?
  4. Apr 5, 2010 #3
    I'm using F(max) = qvB because it seems that it's 90 degrees. The field should be 90 degrees relative to the upward force, so the field is perpendicular, or horizontal, right?

    Also, because of the charge on the electron, i get a negative answer (in Tesla). does this mean that i indicate the negative charge as "eastward?"

    please see attached. thank you!

    Attached Files:

  5. Apr 5, 2010 #4


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    I think if it is negative then your field should be pointing in the opposite direction that you took as the +ve direction.
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