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Homework Help: Capacitance of axon

  1. Jan 22, 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 x 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 4.70 x 10^-6 m^2, what is its capacitance?

    in Farat



    2. Relevant equations



    3. The attempt at a solution
    here is the equation:
    View attachment untitled.bmp

    there are other numbers being used as an example. I just don't know what to use for E0 if E = V/R, and I don't have V, so how do i solve this. thanks.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jan 22, 2008 #2
    There is a simple formula for the capacitance of a parallel plate capacitor:

    [tex]
    C = \frac{\epsilon_o A}{d}
    [/tex]
     
  4. Jan 22, 2008 #3
    Ya thanks for the formula, but i still don't know what E0 is????
     
  5. Jan 23, 2008 #4
    permittivity of free space! 8.85418782 × 10-12 m-3 kg-1 s4 A2
     
  6. Jan 23, 2008 #5
    yes.. but it won't work in this case, as the medium is different than free space [di-electric constant = k = 5, here]. So the formula will be:

    [tex]
    C = \frac{\epsilon_o kA}{d}
    [/tex]

    where k [in this example] is 5.
     
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