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***Can\'t solve for C A simplified model for an erythrocyte is a spherical capac

ID: 1872177 • Letter: #

Question

***Can't solve for C

A simplified model for an erythrocyte is a spherical capacitor with a positively charged liquid interior of surface area A. The interior fluid is separated by a membrane of thickness b from the surrounding, negatively charged, plasma fluid. The potential difference across the membrane is 108 mV, and the thickness of the membrane is about 100 nm with a dielectric constant of = 4.7.Use 1.06 g/cm3 as the density of blood.

(a) Calculate the volume of the blood cell assuming that an average erythrocyte has a mass 1 1012 kg. From the volume determine the surface area of the erythrocyte (in m3).

9.43e-16 volume m3

4.7e-10 surface area m3

(b) Calculate the capacitance of the blood cell. For this calculation, model the membrane as a parallel plate capacitor with the area found in part (a).

1.95e-13

(c) Calculate the charge on the surface of the membrane (in m2). How many elementary charges does this represent?

volume m3

surface area m2

Explanation / Answer

C) Charge, Q = C V = 1.95 x 10-13 x 0.108 = 2.106 x 10-14 C

n = Q/ e =  2.106 x 10-14 C/ 1.6 x 10-19 C = 131625 electrons

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