•• bio a typical cell has a membrane potential of −70 mv, meaning that the potential inside the cell is 70 mv  c 1 = 10 μ f c 2 = 20 μ f 1 2 c  1 2 v = 0 v r 1 = 0.50 mm r 2 = 3.0 mm not for distribution in problems 75 through 77 you are given the equation(s) used to solve a problem. for each of these, you are to a. write a realistic problem for which this is the correct equation(s). b. finish the solution of the problem. 75. where a is a constant with units of v/m 76. 77. challenge problems 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-μm-diameter cell with a 7.0-nm-thick cell wall whose dielectric constant is 9.0?