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Homework Help: Finding the magnitude of an electric field.

  1. Sep 3, 2011 #1
    1. The problem statement, all variables and given/known data
    Determine the magnitude of the electric field at a point midway between a -8.1μC and a 8.9μC charge 8.0cm apart. Assume no other charges are nearby.
    Determine the direction.
    (Answer in two sig figs.)

    2. Relevant equations

    3. The attempt at a solution

    I drew this: -8.1---------p----------8.9

    This is what I think I'm supposed to do.

    The field due to -8.1 charge points toward it.
    The field due to 8.9 points away. So they are both pointing towards the negative charge?

    so E=k/.08^2(8.1e-6+8.9e-6)=2.4e7 N/C but this is incorrect. Please explain why! Thanks.
    Last edited: Sep 3, 2011
  2. jcsd
  3. Sep 3, 2011 #2
    I want to slap myself now...is it because r=.04m? Want assurance because I'm on my last strike.
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