Question

Please answer this very simple conceptual physics question: Regarding a parallel plate capacitor-- Explain something different between the potential inside the plates compared to potential outside the plates.

Answer 1

Parallel plates have a uniform E field between them, ignoring edge effects. So the voltage changes linearly with position.

For example. Pick a zero for voltage, say the negative plate. The other plate is +V. The electric field points from the +V plate to the 0 V plate and E =V/d. That's the slope of the line when you plot V vs x, for example. ∆V = -Ed cos theta. Since you want magnitude, ignore the minus sign, and since you are moving directly perpendicular to the plates, you can ignore the cos theta. So ∆V = Ed.

The electric field outside of any capacitor plates is zero.If we take the negative plate to be at ground potential then the positive plate's potential will be V=ExdV=Exd (E is the electric field and d is the distance between the plates).The potential beyond the positive plate will remain constant at V since the Electric field is Zero beyond it.

Note that the electric field outside of any capacitor is not zero. It is zero only for the ideal case of a perfect infinite parallel plate capacitor.