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Disk and Electric Field's Direction

  1. Jan 26, 2007 #1
    1. The problem statement, all variables and given/known data

    A thin disk with a circular hole at its center, called an annulus, has inner radius R1 and outer radius R2. The disk has a uniform positive surface charge density omega on its surface.

    Figure's link: http://i131.photobucket.com/albums/p289/SoaringCrane/yf_Figure_21_421.jpg

    Find the direction of the electric field E. Consider points above the annulus in the figure.

    2. Relevant equations

    This part of the question is really conceptual.

    3. The attempt at a solution
    Since the disk's overall charge is positive, the force of a positive test charge above the annulus would be directed away from the hole. Therefore, the electric field's direction would be in the positive x-direction??

  2. jcsd
  3. Jan 26, 2007 #2


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    Staff Emeritus
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    Gold Member

    You are correct but can you show it using a vector diagram?
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