Please help me understand this?

Question

Two parallel plates are separated by 5 cm. Plate #1 has a potential of 45 V and Plate #2 has a potential of -20V. Both are constant, what forces would be felt at the following if an electron were placed:

a) directly between the two
b) 1 cm from the -20 V plate
c) 1 cm from the 45 V plate

I don't understand any of this!!
Can someone explain not only how to do this problem, but how I would figure it out in other situations?

Answer 1

The field between a pair of plates is constant. The field

E = V/D = Potential Difference / Plate Separation

= 65 / 0.05 = 1300V/m

The force = Eq = Field X charge = 1300 X 1.6E-19 = 2.7 E-16 N

As the field is constant, the force is the same for parts a), b) and c)

Answer 2

"I don't understand any of this!!"

That's because you didn't do the earlier problems in the chapter on electrostatics, most likely because they seemed trivial. Go back and do them: they'll show you how an electric field pushes or pulls a charged object like an electron, and give you formulas for finding the forces involved. Once you do those, the parallel-plate case will become obvious.