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Homework Help: Magnitude and Direction of a Magnetic Field at the Circumference of a Disk

  1. May 2, 2012 #1
    1. The problem statement, all variables and given/known data

    A very thin disk of non-conducting material initially holds a charge QO = +5 μC that decreases with time t as

    Q(t) = QO e-t/τ
    where τ = 10 seconds.
    If the disk has a radius of 0.10 m, what is the magnitude and direction of the magnetic field at the circumference of the disk as a function of time?

    2. Relevant equations
    Assume at any time t that the displacement vector D is uniform across the disk.
    There is no free current.

    ∇[itex]\bullet[/itex]E = (1/εO

    ∇×B = μOJ + μOεO (∂E/∂t)
    3. The attempt at a solution

    I tried to just work out the curl of B and I immediately ran into problems and it's not correlating to the problem.
    Last edited: May 2, 2012
  2. jcsd
  3. May 2, 2012 #2


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    Show your work. Don't just describe what you did generally.
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