The frequency of an AC circuit refers to:

The frequency of an AC (alternating current) circuit is defined as the number of cycles completed every second, which is measured in hertz (Hz). This is fundamental in understanding AC circuits, as it determines how often the current alternates direction within a given time frame.

In an AC circuit, the voltage and current oscillate between positive and negative values, making frequency a critical parameter. For example, in the United States, the standard frequency for AC power is 60 Hz, meaning the current completes 60 full cycles of negative to positive and back each second.

The other options relate to different electrical properties: voltage measures the electric potential difference, total current refers to the flow of electrical charge, and resistance is the opposition to current flow in a circuit. These concepts are distinct from frequency, which specifically addresses the behavior of the alternating current over time. Understanding frequency is essential for analyzing and designing circuits that utilize AC power effectively.