Capacitors are represented by the letter C, and intuitively understood, capacitors are "containers that store charge". There are many varieties of capacitors, but the basic structure and principle are the same. That is, two pieces of metal that are very close together are separated by a substance (solid, gas or liquid), which constitutes a capacitor. The two pieces of metal are called plates, and the material in between is called the medium. If the capacitor is charged, charge will accumulate on the two electrode plates of the capacitor, and the capacitor has the role of energy storage. The higher the voltage at both ends of the capacitor, the more charge it holds, that is, the greater the energy storage. However, the electric strength of the insulating medium between the two plates of the capacitor is limited, if the electric field strength between the two plates is too high, it may break down the insulating medium, thereby short-circuiting the capacitor.

Capacitors are mainly used for charge storage, AC filtering or bypass, cutting off or blocking DC voltage, providing tuning and oscillation, etc., and are widely used in circuit isolation through alternating, coupling, bypass, filtering, tuning loop, energy conversion, control and so on.