A capacitor is a passive two-terminal component that stores electrical energy within its container. Basically, it consists of two electrical conductors separated by an insulator that stores electrical energy. While capacitors come in all shapes and sizes, they typically have the same basic components. The two conductors are called plates and the insulator is called the dielectric. The two plates inside a capacitor are wired to two electrical connections on the outside called terminals, which are like thin metal legs you can hook into an electric circuit.
A capacitor is similar to a battery, with the main difference being the rate at which the electrical energy is released. A battery uses chemicals to store electrical energy and releases it very slowly through a circuit; sometimes taking several years. A capacitor usually releases its energy much more rapidly—often in seconds or less.
You can charge a capacitor simply by wiring it up into an electric circuit. When you turn on the power, an electric charge gradually builds up on the plates. One plate gains a positive charge and the other plate gains an equal but opposite negative charge. When you turn off the power, the capacitor holds of its charge (although it may slowly leak over time). If you then connect the capacitor to a second circuit containing something that will pull or discharge the energy, like an electric motor, the charge will flow from the capacitor through the motor until there's none remaining on the plates.
The conductors may be foil, thin film, sintered beads of metal, or an electrolyte. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica and oxide layers. Many capacitors have their values printed on them, some are marked with 3-digit codes, and a few are color coded. Check out our RESOURCES page for more helpful info!