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

This starts with the structure of capacitors. The simplest capacitor is composed of two end plates and an insulating dielectric (including air) in the middle. After being powered on, the plates become charged, forming a voltage (potential difference), but due to the insulating material in the middle, the entire capacitor is non-conductive. However, this situation occurs under the premise that the critical voltage (breakdown voltage) of the capacitor is not exceeded. We know that any substance is relatively insulating, and when the voltage at both ends of the substance increases to a certain extent, the substance can conduct electricity. We call this voltage breakdown voltage. Capacitors are no exception. Once a capacitor is broken down, it is no longer an insulator. However, in middle school, such voltage is not visible in circuits, so it works below the breakdown voltage and can be seen as an insulator.

However, in AC circuits, the direction of current changes as a function of time. The process of charging and discharging capacitors takes time, and at this time, a changing electric field is formed between the plates, which is also a function of time. In fact, current passes between capacitors in the form of a field.

In middle school, there is a saying that goes, 'Connect AC and Resist DC', which refers to the property of capacitance.