Suppose that resting on your non-conducting desktop is a tiny piece of paper (m= 0.08 g) that happens to carry a charge of +4x10^-10 C. You comb your hair, and then slowly lower your comb toward the paper until, when it is 3 cm away, the paper jumps up to the comb. Give an approximate value for the charge on the comb. Does the comb carry an excess of electrons or of protons? How many?