A light spherical balloon is made of conducting material. It is suggested that it could be kept spherical simply by connecting it to a high-voltage source. The balloon has a diameter of 100 mm. (a) What is the voltage of the source if the electric field on the balloon surface is 5x10^6 V/m? (b) What gas pressure inside the balloon would produce the same effect? (c) The voltage source is removed and the balloon remains at the same voltage. Calculate the total electrostatic energy of the balloon.