A capacitor is a tool consisting of two conductive plates, each of which hosts an opposite charge. These plates are separated by a dielectric or other form of insulator, which helps them maintain an electric charge. There are several types of insulators used in capacitors, including ceramic, polyester, tantalum air, and polystyrene. Other common insulators include air, paper, and plastic. Each effectively prevents the plates from touching each other.
There are a number of different ways to use a capacitor, such as to store analog signals and digital data. Another type is used in the telecommunications equipment industry to adjust the frequency and tuning of telecommunications equipment. This is often referred to a variable capacitor. A capacitor is also ideal for storing electrons, but it cannot make them.
The first capacitor was the Leyden jar, invented at the Netherlands University in the 18th century. It consists of a glass jar coated with metal on the inside and outside. A rod is connected to the inner coat of metal, passed through the lid, and topped off with a metal ball. As with all capacitors, the jar contains an oppositely charged electrode and a plate that is separated by an insulator. The Leyden jar has been used to conduct experiments in electricity for hundreds of years.
A capacitor can be measured in voltage, which differs on each of the two interior plates. Both plates are charged, but the current flows in opposite directions. A capacitor contains 1.5 volts, which is the same voltage found in a common AA battery. As voltage is used, one of the two plates becomes filled with a steady flow of current. At the same time, the current flows away from the other plate.
To understand the flow of voltage in a capacitor, it is helpful to look at naturally occurring examples. Lightning, for example, works in a similar way. The cloud represents one of the plates and the ground represents the other. The lightning is the charging factor moving between the ground and the cloud.
Source / Courtesy : WiseGeek