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Electric fields

  1. Dec 11, 2013 #1
    1. The problem statement, all variables and given/known data

    Find the net electric field strength at point A due to the combined electric fields of both charges.

    2. Relevant equations


    3. The attempt at a solution
    I know how to solve these type of problems however I'm just wondering how come in the net force line as you can see on my paper, they didn't use a -3.7*10^7 since it is going in the left direction.

    The answer that was given was : 3.7*10^7+ 7.71*10^6 = 4.5*10^7 N/C

    When I did electrostatic forces before that had charges in a line, you had to use negative when finding net force for charges that went to the left..

    Attached Files:

  2. jcsd
  3. Dec 11, 2013 #2


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    I agree with your line of thought :smile:. The magnitude of the net E field should be|-3.7*10^7+ 7.71*10^6|. The magnitudes of the individual fields should be subtracted because the individual electric field vectors point in opposite directions at point A.

    [EDIT: To avoid giving people stiff necks, it would be nice to post your images so they are upright. :wink:]
    Last edited: Dec 11, 2013
  4. Dec 11, 2013 #3
    So you are saying that the answer that was given was wrong?
  5. Dec 11, 2013 #4


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    Yes. If one charge is positive, the other charge is negative, and the point A is located as shown in your diagram, then the given solution is wrong.
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