Dielectrics in Capacitors
When viewed as a whole, is a capacitor that stores a certain amount of charge electrically neutral or electrically charged?
The answer is that the two plates of a capacitor store the same amount of charge but with opposite signs. That means that the capacitor is actually neutral, even when it is said to store a large amount of charge! If you could probe the space between the capacitor plates, you would feel electric forces because each plate individually is charged.
But viewed from the outside (at a distance much larger than the plate separation), the forces from the oppositely charged plates would cancel each other, so there is practically no electric field. This is why capacitance, and not field strength, is the quantity that we care most about when using capacitors in practice.
It is not usually feasible to build capacitors just by placing two parallel metal plates opposite each other with an air gap in between. Instead, you fill the space between the conductors with a different insulating material, called a dielectric. This is not just for mechanical stability – it actually enhances the functionality of the capacitor.
Watch this lecture to see how this works.
Source: Khan Academy, https://youtu.be/rkntp3_cZl4 This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License.