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Homework Help: Application of Gauss's Law

  1. Apr 27, 2005 #1
    A flat square sheet of thin aluminum foil, 25 cm on a side, carries a uniformly distributed -36 nC charge. What is the approximate electric field at the following positions?

    a.)0.01m above surface?
    b.) 20m above the sheet?

    For a.), I used E=chargedensity/(2)epsilon. From my understanding, this can only be used for points far from the edges and close to a surface.

    So for b.), this formula does not apply. I cannot find anything in my notes or the text that describes this situation.

    Any suggestions?
  2. jcsd
  3. Apr 27, 2005 #2

    Doc Al

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    Staff: Mentor


    Hint: If you are far enough away, you can treat the object as a charged particle.
  4. Apr 27, 2005 #3


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    Try breaking it down. If the charge on the plate were a single point charge, what would the field be? If the charge was split into two point charges separated by 25 cm, how much would this change the result? What about 3 or 4?
  5. Apr 27, 2005 #4
    damn, I tried that earlier because it seemed like as you got further and further away, the sheet would appear small (like a pt charge).....only problem was....I forgot to square the 20m :grumpy:
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