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Homework Help: The Electric Field Due to a Charged Disk

  1. Jan 25, 2009 #1
    1. The problem statement, all variables and given/known data
    A circular plastic disk with radius R = 1.80 cm has a uniformly distributed charge of Q = + 2.15 106 e on one face. A circular ring of width 30 µm is centered on that face, with the center of the ring at radius r = 0.50 cm. What charge is contained within the width of the ring?

    2. Relevant equations
    E=σ/2ε(1-z/√(z^2+R^2 ))

    3. The attempt at a solution

    o= 2.15e6
    z=.5 cm
    r= 1.8
    Ans=3.15 e10
  2. jcsd
  3. Jan 25, 2009 #2


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    Homework Helper

    I don't see it as an electric field question. The question asks "what charge ...".
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