two large charged plates of charge density ±40 nc/m2 face each other at a separation of 7.0 mm. (a) find the electric potential everywhere. (assume the negatively charged plate is at the origin and the positively charged plate is at 7.0 mm in the z-direction. define the potential to be zero at the origin. use the following as necessary: z. assume v is in volts and z is in meters. do not include units in your answers.)