Of course, we all know that capacitors are conceptually two conductors separated by a dielectric of some sort. But outside of air-variable capacitors you normally don’t see them looking like that. For example, a film capacitor has its plates rolled up in a coil with an insulating film in between. You can’t really see that unless you take them apart. But [Electronoobs] makes some giant capacitors using large plates and does a few experiments to demonstrate their characteristics. You can see his work in the video below.
The arrangement reminded us of a Leyden jar except there’s no physical motion. He also had some entertaining footage of electrolytic capacitors exploding when connected backwards. The reason, by the way, is that electrolytic capacitors have conductive goo in them. By putting a controlled current through them during manufacturing, a very thin insulating layer forms on one electrode. The thinner the layer, the higher the potential capacitance is. The downside is that putting current in the opposite way of the formation current causes catastrophic results, as you can see.
The value of a capacitor depends on the area, the spacing, and the type of dielectric between the plates. The video covers how each of those alters the capacitor value. Real capacitors also have undesirable characteristics like leakage and parasitic resistance or inductance.
It used to be that capacitance meters were exotic gear, but these days many meters have that capability. This would be a great set of experiments for a classroom or as the basis for a kid’s science project. For example, measuring different dielectric materials to determine which is the best for different purposes.
Granted, capacitors are pretty basic physics, but it is easy to get wrapped up in using them and not think about what’s going on inside. This video is a good introduction or a refresher, if you need one. It is easy enough to make your own variable capacitors or even special capacitors for high voltages.