Consider a long cylindrical capacitor (see figure on the right) wherein the separation distance d between its plates is very small (ra and ro are just slightly different) such that d << ra. Show that its capacitance is equivalent to a parallel-plate capacitor C = ɛ,A/d and explain why this cylindrical capacitor can be treated as a flat capacitor.

Consider a long cylindrical capacitor (see figure on the right) wherein the separation distance d between its plates is very small (ra and ro are just slightly different) such that d << ra. Show that its capacitance is equivalent to a parallel-plate capacitor C = ɛ,A/d and explain why this cylindrical capacitor can be treated as a flat capacitor.