일반물리학 2 — Electric Potential: Problem 53

53 A spherical drop of water carrying a charge of 30 pC has a potential of 500 V at its surface (with V = 0 at infinity). (a) What is the radius of the drop? (b) If two such drops of the same charge and radius combine to form a single spherical drop, what is the potential at the surface of the new drop? (c) What is the ratio of the surface charge density on the new drop to that on the original drop?