It is internationally stipulated that when a DC voltage of 1 volt is applied to a capacitor, the amount of charge it can store is the capacitance of the capacitor (that is, the amount of electricity at unit voltage), which is represented by the letter C.

The basic unit of capacitance is farad (f). Under the DC voltage of 1V, if the charge stored in the capacitor is 1 coulomb, the capacitance will be defined as 1 farad, which is represented by the symbol f,1f =1q/v.

In practical applications, the capacitance of capacitors is often much smaller than 1 farad, and smaller units are often used, such as millifarad (mF), microfarad (μF), nanofarad (nF), picofarad (pF) and so on.

Extended data

The role of the capacitor:

Coupling, the capacitance used in coupling circuits is called coupling capacitance, which is widely used in capacitive coupling circuits such as resistance-capacitance coupling amplifiers to block DC, DC and AC.

Filters, capacitors used in filter circuits are called filter capacitors, which are used in power filters and various filter circuits to remove signals in a certain frequency band from the total signal.

Decoupling, the capacitor used in decoupling circuit is called decoupling capacitor, which is used in DC power supply circuit of multistage amplifier, and it eliminates harmful low-frequency cross-connection between amplifiers at all levels.

High frequency vibration elimination, the capacitor used in high frequency vibration elimination circuit is called high frequency vibration elimination capacitor. In the audio negative feedback amplifier, in order to eliminate the possible high-frequency self-excitation, this capacitor circuit is adopted to eliminate the possible high-frequency howling of the amplifier.

References:

Baidu encyclopedia-capacitor