Using the result that the plates of a parallel-plate capacitor attract each other with a force given by

we have to show that the force per unit area (the electrostatic stress) acting on either capacitor plate is given by . This result is true, in general, for a conductor of any shape with an electric field at its surface.

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Let us consider a parallel-plate capacitor of plate area A. let the capacitor be charged with charge q. The plates attract each other with force

Therefore, force per unit area on each plate is

Electric field between the plates of a parallel-plate capacitor is

Therefore, electrostatic stress on each plate can be expressed by