Need help describing electric potential and electric field (2 questions)

Question

1. If a proton is held between two charged plates and it moves in the direction of the electric field, what happens to the electric potential?

 

2. If the electric potential is constant between two plates, what happens to the electric field?

Answer 1

(1)

 

A free positively charged particle will accelerate in the direction of decreasing electric potential.  Think of it as the electric field pushing the positive particle down a potential hill.

 

(2)

 

If the electric potential is constant, the electric field is zero.  Recall that the electric field is the negative gradient of the electric potential, so if the potential is constant over a region, there cannot be an external electric field in the region.