Some cell walls in the human body have a layer of negative charge on the inside surface and a layer of positive charge of equal magnitude on the outside surface. Suppose that the charge density on either surface is ± 0.50×10?3 C/m2, the cell wall is 5.00nm thick, and the cell-wall material is air. A typical cell in the human body has a volume of 10?16m3 . Estimate the total electric-field energy stored in the wall of a cell of this size. (Hint: Assume that the cell is spherical, and calculate the volume of the cell wall.)