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Homework Help: Determining Electric Field

  1. Sep 2, 2008 #1
    1. The problem statement, all variables and given/known data
    Determine the electric field E at the origin 0 in fig 16-56 due to the two charges at A and B. b.) Repeat, but let the charge at B be reversed in sign. I can;t find the figure online, so I'll have to describe it. Charge A is on the vertical axis distance L from the origin with charge B to the lower right at a distance of L which is also a distance of L from the origin. The origin, Charge A, and Charge B form an equilateral triangle. Charge A and B for the first part are both +Q.

    2. Relevant equations
    tan^-1(y/x) = theta

    3. The attempt at a solution
    I understand that the electric field has to be calculated then the components added as vectors, and I understand how the answer in the back of the book was set up, except that the answer is the square root of 3 times k*q/L^2. I don't see how they could have gotten the square root of three with so little detail in the problem, but I'm assuming it has something to do with the angle between them? I've finished all my other more advanced problems but I'm still stumped by this one. Once I get the components I'll be able to calculate the angle, but I'm wondering how they got what they did. Thanks, all help is appreciated! Again, sorry for lack of diagram.
  2. jcsd
  3. Sep 3, 2008 #2


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    Homework Helper
    Gold Member

    Notice that they tell you that the charges form an equilateral triangle with the origin. What are the angles of an equilateral triangle equal to?

    Assuming I am picturing this correctly, you should be able to use this information to get the components in terms of just q and L.
  4. Sep 3, 2008 #3
    Thanks, but I got it in school today. Wasn't very hard, but took a bit of algebra and vector addition. Thanks anyway!
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