In an AC circuit, what is the role of a capacitor?

In an AC circuit, the role of a capacitor is primarily to block direct current (DC) while allowing alternating current (AC) to pass. This functionality is rooted in the way capacitors interact with different types of electrical signals. When a DC voltage is applied across a capacitor, it charges up to that voltage and stops the flow of current, effectively blocking DC. However, in the case of an AC signal, which continuously varies in polarity, the capacitor charges and discharges in sync with the changes in the AC waveform. This allows AC to flow through the circuit, while DC conditions are restricted.

The other options do not accurately describe the core function of a capacitor in an AC circuit. While capacitors can have some relationships with voltage and frequency, their primary role in AC applications is as described. By blocking DC and allowing for AC passage, capacitors are often utilized in coupling and decoupling applications, filtering circuits, and signal processing tasks.