Capacitance is a circuit device made according to the capacitance effect. It maximizes the capacitance effect and gathers charges as much as possible to form a large enough electric field and store the corresponding electric field energy.
Capacitors are widely used in engineering technology, with various types, models and specifications, but the structure principle is the same. In short, two metal plates close to each other are sandwiched with a layer of non-conductive insulating medium (such as insulating paper, mica, air, etc.), which constitutes a capacitor.
When a voltage is applied between two metal plates of the capacitor, that is, an external electric field is applied. Under the force of the external electric field, the charge of the metal plate will gather. For example, the positive charge of the metal plate connected to the positive pole of the external voltage (the positive pole of the power supply) will gather in the direction between the two plates due to the repulsion force. Similarly, the negative charge of the other metal plate will also gather in the direction between the two plates.
With the charge accumulation, an electric field is established between the two metal plates of the capacitor, that is, a certain amount of electric field energy is stored, which is the energy storage property of the capacitor. In a word, the energy absorbed by the capacitor is stored in the electric field between the plates in the form of electric field energy.
The modeling of capacitor in circuit analysis is the capacitor element. The capacitor element is an ideal element, which only reflects the physical phenomenon that the capacitor can store charges (store electric field energy). Its circuit symbol is two short vertical lines. These two short vertical lines are just like two metal plates, which can be said to be very visual.
Capacitors are widely used and play different roles in different circuits, such as coupling, filtering, rectification, reactive power compensation, etc.