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Homework Help: Electric field on a disk

  1. Jan 6, 2010 #1
    1. The problem statement, all variables and given/known data

    A charge of -5.00 nC is spread uniformly over the surface of one face of a nonconducting disk of radius 1.15 cm. Find the magnitude of the electric field this disk produces at a point P on the axis of the disk a distance of 3.00 cm from its center.

    2. Relevant equations

    Surface area element for a disk [sigma]= Q / A

    See attachments

    3. The attempt at a solution

    So I plugged the numbers in accordingly, had no luck.

    I appreciate the help.

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  2. jcsd
  3. Jan 6, 2010 #2
    I'm working on uploading a picture of my attempt.
  4. Jan 6, 2010 #3
    ... uploaded

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  5. Jan 6, 2010 #4


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    Homework Helper

    That equation only applies for infinitely large plates. This disk is not infinitely large.

    Try using E=kq/r^2 to get the electric field due to the charge on one infinitely thin ring surrounding the center of the disk. Then, integrate over the disk.
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