A simplified model for an erythrocyte is a spherical capacitor with a positive inner surface of area A and a membrane of thickness b. Use potential difference of 94 mV across the membrane and a dielectric constant K = 5.0. If the capacitance of the membrane is C = 0.15 pF, what is the radius of the erythrocyte? The thickness of the membrane is b = 90 nm.

Question

The way I thought to solve for this question was that I found the area using the Capacitance of a dielectric eqn, then from there used A = pi*r^2 to solve for r...is this the correct approach? I'm just concerned because I'm not using the potential difference anywhere...

Answer 1

The membrane surface area should be
A = 4 pi r^2
for a spherical cell

Answer 2

Thanks, so there wouldn't be any need to use the potential difference anywhere right?

Answer 3

No, no V. Capacitance is not dependent on potential.

Answer 4

Isnt capacitance defined as how much charge per unit potential?