On a humid day, an electric field of 2.00 * 10^4 N/C is enough to produce sparks about an inch long. Suppose that in your physics class, a van de Graaff generator with a sphere radius of 15.0cm is producing sparks 6 inches long. a) Use Gauss's law to calculate the amount of charge stored on the surface of the sphere before you bravely discharge it with your hand. b) Assume all the charge is concentrated at the center of the sphere, and use Coulomb's law to calculate the electric field at the surface of the sphere.