Capacitors/dielectrics q from p2 e&m college level?

Question

any help would be appreciated. :)

An axon is the relatively long tail-like part of the 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 5 x 10^-6 m^2, what is its capacitance?

Answer 1

Parallel plate cap

C = ε₀εr(A/d)

   ε₀ is 8.8542e-12 F/m

   εr is dielectric constant (vacuum = 1)

   A and d are area of plate in m² and separation in m

C = 8.9e-12*5(5e-6/1e-8) = 220 e-10F or 22 nF