# Voltage difference between two surfaces

How would you find voltage difference between two surfaces? If you are given a capacitor with an internal electric field that varies E. You also have the charge (sigma) and the radius of the inner surface r1 and the radius of the outer surface r2.

Well, since you know the stored charge and geometry, just solve the Poisson equation. However, since you seem to know the electric field it may be simpler just to integrate it.