Question

1. what is the relationship between the electric field and the electric potential BETWEEN THE PLATES OF CAPACITOR?

Answer 1

The relationship is the following (see https://www.youtube.com/watch?v=HmZ4iK1T1bg):

$$E = \dfrac{V}{d}$$

where $E$ is the electric field, $V$ is the electric potential, and $d$ is the distance between the plates.