13.Consider a metal conductor in the shape of a football. If it carries a total charge Q, where would you expect the charge density δ to be greatest, at the ends or along the flatter sides? Explain.(Hint: Near the surface of a conductor, E=δ/ε0). 14.A conducting sphere carries a charge Q and a second identical conducting sphere is neutral.The two are initially insulated, but then they are placed in contact. (a)What can you say about the potential of each when they are in contact? （b）Will charge flow from one to the other? If so, how much? (c)If the spheres do not have the same radius, how are your answers to parts (a) and (b) altered? 19.Is the electric potential energy of two unlike charges positive or negative? What about two like charges? What is the significance of the sign of the potential energy in each case? 13.I think the density at the ends is greater because the smaller the area, the more charge will gather? 14.(a)They have potential difference. (b)It will. Half of Q. (c)There still exists potential difference. The charge will flow, but not half of Q. The amount will depens on the ratio of the area of two spheres. 19.The electric potential energy of two unlike charges may be neutral? Two positive charges has positive energy and negative charges has negative charges. The sign of the potential energy determines the sign of energy.