Two metal plates placed parallel to each other without touching each other can form a simplest capacitor.

Capacitors have the characteristics of blocking DC and communicating AC.

1 Connect the two pins of the capacitor to the positive and negative poles of the power supply, and the power supply will charge the capacitor. When the voltage charged by the capacitor is equal to the power supply voltage, the charging will stop, and there will be no current flow in the circuit, which is equivalent to an open circuit. .

2 When the switch in the circuit is turned off, the capacitor will discharge through the resistor, and its current direction is opposite to the current direction when charging. As the current flows, the voltage across the capacitor gradually decreases until it disappears completely.

Two important functional characteristics of capacitors:

(1) Prevent the passage of DC current and allow the passage of AC current;

(2) The impedance of the capacitor is related to the frequency of the transmitted signal. The higher the signal frequency, the smaller the impedance of the capacitor.