The electric potential at the center of a square is -1 V when a charge -Q is placed in one of the corners. Required:What will be the electric potential at the center when three additional charges of -Q are placed at the three other corners of the square?

Students in an introductory physics lab are performing an experiment with a parallel-plate capacitor made of two circular aluminum plates, each 11 cm in diameter, separated by 1.0 cm. how much charge can be added to each of the plates before a spark jumps between the two plates? for such flat electrodes, assume that value of 3×106n/c of the field causes a spark.