A simplified model for an erythrocyte is a spherical capacitor with a positively

Question

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 113 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).

volume  m3surface 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).

(c)

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

volume  m3

surface area  m2

please answer c its not just the answer to b / 1.6x10-19

Explanation / Answer

we have capacitance c = Q/V

     then charge Q = CV

V = 113 * 10 ^-3 V is given and from (b) C was known

substituting we get Q charge on the surface of the membrane.

to get the number of charges ..now the charge Q is divided by 1.6 * 10 ^-19

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