A pair of parallel plates at 4 cm apart is connected to a battery. When a proton is placed at a point 1 cm from the positive plate, the electric force on the proton is 1.6x10^-5 N. When the proton is placed at a point 1cm from the negative plate,
a) what is the electric force on the proton?
b) what is the p.d. between the final and initial positions of the proton?
take e=1.6x10^-19 C.