A Level Physics-Electric Fields helpWatch
Potential Difference = (Force / Charge) x Distance
But this formula only works when the Force on the Charge is Constant and the Electric Field is Constant (NOT TRUE for point charges)
Clearly, thus is not the case so we have to revert to calculus and say that
THE AREA Under the Force - Distance graph is the Energy or Work Done.
But you have a graph of Electric Field v Distance so you need to make a factor adjustment of this. Force = Electric Field x Charge
The equation or expression V = Ex is actually
in the disguise.
If a point charge Q is responsible for the electric field, then the magnitude of electric field strength of the point charge Q is
and the electric potential due to the point charge Q is