In Figure 8, plate A is at higher potential and B is a lower potential. As a positive charge accelerates towards plate B, its electric potential energy decreases with distance. In this case, the electric field can be defined in terms of the variation of electric potential
at different points in the field. The potential gradient in an electric field is a vector, which is defined as the rate of change of electric potential with respect to displacement in the direction of the field. The magnitude of potential gradient is given by

where E is electric field strength (V/m), ∆ V is change in potential (V), ∆ r is displacement in the direction of the field (m).