A model of a red blood cell portrays the cell as a spherical capacitor, a positi

Question

A model of a red blood cell portrays the cell as a spherical capacitor, a positively charged liquid sphere of surface area A separated from the surrounding negatively charged fluid by a membrane of thickness t. Tiny electrodes introduced into the interior of the cell show a potential difference of 100 mV across the membrane. The membrane's thickness is estimated to be 101 nm and has a dielectric constant of 5.00.
(a) If an average red blood cell has a mass of 1.2e-12 kg, estimate the volume of the cell and thus find its surface area. The density of blood is 1100 kg/m3.
volume = ___1.09e-15____m3
surface area = ________m2
(b) Estimate the capacitance of the cell by assuming the membrane surfaces act as parallel plates.
____________F
(c) Calculate the charge on the surface of the membrane.
______________C
How many electronic (elementary) charges does the surface charge represent?
___________________________________________________________________________

Explanation / Answer

I'm not sure how to do part b, but for part a:
m = 1.1e-12 kg
rho = 1100 kg/m3

V = m/rho
= 1.1e-12/1100
= 1e-15 m3

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