Posted by Sandra on .
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.
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...

Physics 
drwls,
The membrane surface area should be
A = 4 pi r^2
for a spherical cell 
Physics 
Sandra,
Thanks, so there wouldn't be any need to use the potential difference anywhere right?

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

Physics 
Anonymous,
Isnt capacitance defined as how much charge per unit potential?