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Homework Help: Homework on Capacitors

  1. Feb 4, 2008 #1
    1. The problem statement, all variables and given/known data

    An axon is the relatively long tail-like part of a neuron, or nerve cell. The outer surface of the axon membrane (dielectric constant = 5, thickness = 1 *10-8 m) is charged positively, and the inner portion is charged negatively. Thus, the membrane is a kind of capacitor. Assuming that an axon can be treated like a parallel plate capacitor with a plate area of 5.50 * 10-6 m2, what is its capacitance?

    2. Relevant equations

    C= EoA/d where Eo= permittivity of free space = 1/(4*Pi*k) k= 8.99E9
    A = area d= seperation of plate

    3. The attempt at a solution

    I first solved for the permittivity of free space and got that answer to be 8.85E-12, then I plugged that in for Eo, 5.50E-6 for the A, and I was not sure what to do for the d? Use the 5? or 1 E-8? Can anyone help?
  2. jcsd
  3. Feb 4, 2008 #2

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    > C= EoA/d where Eo= permittivity of free space

    C= 5*EoA/d, where 5 is the dielectric constant, d=1*10^-8 m.
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