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Area of a Parallel Plate capacitor. Pi*r^2?

  1. Jan 27, 2008 #1
    Hi,

    I was just going through a question in my Physics textbook today. In calculating the electric field (E=sigma/epsilon0) ... sigma = charge density = q/Area ... they have used the area as pi*r^2, I can't understand why this was done? shouldn't the area of the parallel plate capcitor be length of one electrode * distance between electrodes?

    Hope I'm making sense!
     
  2. jcsd
  3. Jan 27, 2008 #2

    jtbell

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    Staff: Mentor

    No, the area that we use here is the area of one of the electrodes (circular in this case, apparently). The charge resides on the electrodes, not in the space between them.
     
  4. Jan 28, 2008 #3
    Hmm, makes sense. Thanks mate!
     
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