In a DC circuit, a capacitor is equivalent to an open circuit. A capacitor is a component that can store electric charge and is one of the most commonly used electronic components.

This has to start with the structure of the capacitor. The simplest capacitor consists of plates at both ends and an insulating dielectric (including air) in between. After electrification, the plates are charged to form a voltage (potential difference), but due to the insulating material in the middle, the entire capacitor is non-conductive. However, such a situation is under the premise that the critical voltage (breakdown voltage) of the capacitor is not exceeded. We know that any substance is relatively insulating. When the voltage across the substance increases to a certain level, the substance can conduct electricity. We call this voltage the breakdown voltage. Capacitors are no exception. After a capacitor is broken down, it is no longer an insulator. However, in the middle school stage, such voltage is not seen in the circuit, so they all work below the breakdown voltage and can be regarded as an insulator.

However, in an AC circuit, the direction of the current changes as a function of time. The process of charging and discharging the capacitor has time. At this time, a changing electric field is formed between the plates, and this electric field is also a function of changing with time. In reality, the current is passed between the capacitors in the form of a field.

In the middle school stage, there is a saying that it is called to pass AC and block DC, which refers to the nature of capacitance.