Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Capacitance question

  1. Jul 9, 2006 #1
    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 4.7 10-6 m2, what is its capacitance?

    I used the formula C = (KE0 A )/ d

    and assigned the following:
    KE0 = 5
    A = 4.7 x 10^-6 m2
    d = 1 x 10^-8 m

    and came up with:
    C= 2350.
    this isn't correct though.

    What am I doing wrong?
  2. jcsd
  3. Jul 9, 2006 #2
    ok, on further work, i believe it should just be K=5. i dont know what formual to use to find E though...
  4. Jul 9, 2006 #3


    User Avatar
    Homework Helper

    You mean "E0", in your capacitance equation? That's just the permittivity of free space (usually denoted ε with a subscript 0), a constant equal to 8.85x10^(-12) Coulomb^2/(Nm^2).
    Last edited: Jul 9, 2006
  5. Jul 9, 2006 #4
    i got it know
    thank you
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook