Simple Capacitors

In its simplest form, a capacitor is just two conductors with an insulator in-between them. You might consider it a dielectric sandwich. Actually, in their simplest form, capacitors are an idea. You are a capacitor if you're standing on a sheet of plastic (the earth is one conductor, you are the other, and the plastic is the insulator).

Important things to keep in mind regarding capacitors:

Capacitors can build up and store a charge "imbalance," which means one conductor gets charged positively while the other gets charged negatively. This imbalance of charge contains energy. The energy is released if the electricity can find a way to get from one conductor to the other. If there's enough energy, the electricity can "jump" through the air. You see or hear the evidence of this happening as a spark. The smaller the gap it has to cross, the less voltage it takes to jump through the air.

There is so much good information published about capacitors that you shouldn't rely on just one source. A.D Moore's book titled Electrostatics is a good place to start. There are also many different types of capacitors, so be ready to learn and keep an open mind. Finally, it's true that capacitors can be dangerous. Large capacitors or banks of capacitors can hold enough charge to do serious physical damage. Beware, they'll "shock the fool out of you."

Now, how about some ideas to get the brain in gear ?

One of the simplest capacitors you can make takes aluminum foil, a plastic disk, and rubber cement. Plastic lids tend to work well. As you experiment you will find that a smaller area of foil produces a capacitor that charges quicker, and a larger area of foil creates a capacitor that takes a longer time to charge but makes a hotter louder spark when it is discharged. Another variable on the type of capacitor descibed above and below is the distance of the spark gap. Advice: start small with both foil area and spark gap length, to see how things work. Foil disks about the size of quarters on a yogurt lid with an eighth inch spark gap is a good starting point (see below).
 This drawing represents a red plastic plate with a circle of foil glued on with rubber cement. There is an identical circle glued on the other side. The small triangle represents a piece of foil that is glued to the back circle and folded over to create a small spark gap. The jagged edge in the center is a tab of foil that sticks up, so the capacitor can be charged with a plastic rod and fur.
This is what the other side looks like.
Here's another example of what I'm talking about. It is a dismantled floppy disk with red foil gift wrap on each side. The spark jumps between that little red point and the bigger red "kidney" shape.

Another capacitor that is easily constructed is the "Leyden jar" type. This sort of capacitor can be discharged using tongs.

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