# Homework Help: Homework on Capacitors

1. Feb 4, 2008

### sheri1987

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. Feb 4, 2008

### Shooting Star

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

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