A typical cell has a membrane potential of -70 m V , meaning that the potential

Question

A typical cell has a membrane potential of -70 mV, meaning that the potential inside the cell is 70 mV less than the potential outside due to a layer of negative charge on the inner surface of the cell wall and a layer of positive charge on the outer surface. This effectively makes the cell wall a charged capacitor. Because a cell's diameter is much larger than the wall thickness, it is reasonable to ignore the curvature of the cell and think of it as a parallel-plate capacitor.

How much energy is stored in the electric field of a 50-%u03BCm-diameter cell with a 7.0-nm-thick cell wall whose dielectric constant is 9.0?

Explanation / Answer

energy = 1/2cv^2

c= k*epsilon Area/distance = 9*8.85*10^(-12) * 3.14*(25*10^(-6))^2/(7*10^(-9)) = 22.33 *10^-12

so energy = 1/2 * 22.33 * 0.07^2 = 5.47 * 10^-14 J

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