Four charge are placed at four corners of a square that as 30cm on each side. Find the potential at the center of the square If (a) the four charges are each +2.0uC and (b) two of the four charges are +2.0uC and two are -2.0uC.

Agraduated cylinder contains 63.0 ml of water. a piece of gold, which has a density of 19.3 g/ cm3, is added to the water and the volume goes up to 64.5 ml. calculate the mass in grams of the gold that was added to the water. explain how you got your answer.