Capacitor is a device that stores energy created between a pair of conductors. An insulator (also called dielectric) of some kind is usually placed between the plates. The conductors are plates / electrodes which store opposite charges between them. The amount of charge a capacitor can hold can be found by multiplying "capacitance" with the "potential difference" between the plates. Capacitance is the amount of charge that can be stored on a capacitor plate. Silver-Mica - This uses mica as a dielectric. Mica capacitors have good stability because their temperature coefficient is small. Because their frequency characteristic is excellent, they are used for resonance circuits, and high frequency filters. Also, they have good insulation, and so can be utilized in high voltage circuits. It was often used for vacuum tube style radio transmitters, etc. Mica capacitors do not have high values of capacitance, and they can be relatively expensive. Generally, Variable Capacitors - They are also called trimmer capacitors or adjustable capacitors. They usually have ceramic or plastic as a dielectric. Most of them are color coded to easily recognize their tunable size.