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Homework Help: Electric Field between two infinite sheets of Opposite charge.

  1. Sep 7, 2008 #1
    1. The problem statement, all variables and given/known data

    I am having trouble with an E&M conceptual problem. Suppose we have two sheets of infinite charge, one positive and one negative (the positive is left of the negative and they have charge densities given respectively alpha and - alpha.). The problem asks to find the direction and magnitude of the electric field at 4 points in the same line, 2 points outside the sheets of charge, 1 near the positive sheet of charge (from the inside) and 1 in the center of the two infinite sheets of charge.

    3. The attempt at a solution

    Now, i know that the direction of the electric field on the outside will be towards the positive sheet of charge and away from the negative sheet of charge. What about the magnitude?

    In the center the E-field should be in the -x direction since the y components cancel out but still i cant find the magnitude because there is no distance between them given.

    Lastly near the positive sheet of charge(from the inside) i think the e-field should be in the -x direction with a lesser magnitude than in the center.

    I am not sure how to get the magnitudes without the distance separation between them.
  2. jcsd
  3. Sep 7, 2008 #2


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    Homework Helper

    Hi Hells_Kitchen,

    What is the formula for the electric field of an infinite sheet of charge?
  4. Sep 7, 2008 #3
    E = charge density/ epsilon zero. Well that might be the magnitude for the outside points what about for the center and the point inside (in between the sheets)
  5. Sep 7, 2008 #4


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    That's not be the total magnitude for outside points. That formula is the electric field from a single sheet of charge. To find the total field at a single point, you'll need to add the two separate electric field vectors.

    So look at some point between the sheets first. What is the electric field at that point from the positive sheet? (magnitude and direction) What about from the negative sheet? Once you have the magnitude and direction of the two individual vectors, what is their vector sum?
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