Earlier this week during a trip to Halted, we were talking about how capacitors work. We knew the basics: it's a device to store electrical energy, but we were all bleary on how they worked.
Last night I was talking to a hardware engineer and asked her the same question, and I got the same answer: "it's a device to store electrical energy." I pressed: "that's what a capacitor is -- but how do they really work? Like, what causes a capacitor to release its charge? It's only got two terminals, its not like a transistor -- when/how do they work?"
Here's what I got:
A capacitor has two plates inside it separated by a non-conductive substance (the dielectric). Common substances to separate the plates are: air, mylar, glass, or ceramic.
When you connect a capacitor to a battery, the plate connected to the negative terminal begins accumulating (charging) with electrons. The plate on the capacitor connected to the positive terminal loses electrons back to the battery.
Eventually the capacitor is "charged" when it has the same voltage as the battery and electrons stop flowing. At this point, if you take the capacitor out of the circuit, it'll have a static configuration of pile of electrons on the negative plate (and a dearth of electrons on the positive plate).
Put the capacitor into another circuit, and it'll discharge into it, I found this description of Capacitor Charging and Discharging very helpful.
One thing I'm still not remembering: how can you tell a capacitor is fully charged without shorting it? I think you use a big resistor (to keep it from discharging very fast) and an LED in series.