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Homework Help: On (pentagon shaped) electric field question.

  1. May 3, 2012 #1
    1. The problem statement, all variables and given/known data
    Four particles, each having a charge q are placed on the four corners A, B, C, D of a regular pentagon ABCDE. The distance of each corner from the centre is a. Find the electric field at the centre of the pentagon.

    2. Relevant equations
    E=q/(4∏ε0)(a^2) where k=1/4∏ε0

    3. The attempt at a solution
    Well certainly I think it's silly to just sum up four electric fields to give 4q/(4∏ε0)(a^2). I think it would seem obvious that there is a net electric field as shown in the attached diagram. Suppose E(E) exists. Then E(A)+E(B)+E(C)+E(D)+E(E)=0. My working is shown in the diagram attached. At the same time I am confused as how the electric field vectors resolves.
  2. jcsd
  3. May 3, 2012 #2
    Darn, can't upload the diagrams. I've uploaded it on my random blog. Go to www.kcsuploads.blogspot.com and see pentagon diagram. Sorry for any inconvenience caused
  4. May 3, 2012 #3


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    Just add the vectors the way vectors add. Decompose them into their components in a convenient reference frame. Symmetry considerations will help set that up.
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