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. Examples include ceramic, polyester, tantalum air, and polystyrene. Other common capacitor insulators include air, paper, and plastic. Each effectively prevents the plates from touching each other.

A capacitor is often used to store analogue signals and digital data. Another type of capacitor is used in the telecommunications equipment industry. This type of capacitor is able to adjust the frequency and tuning of telecommunications equipment and is often referred to a variable capacitor. A capacitor is also ideal for storing an electron. A capacitor cannot, however, make electrons.

The first capacitor was the Leyden jar, invented at the Netherlands University in the 18th century. This type of capacitor 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 of the capacitor, and topped off with a metal ball. As with all capacitors, the Leyden 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 measures in voltage, which differs on each of the two interior plates. Both plates of the capacitor 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 in a capacitor, 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, is similar to a capacitor. 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.