What role does a capacitor play in an AC circuit?

In an AC circuit, a capacitor plays the significant role of storing and releasing electrical energy. When an alternating current flows through a capacitor, it does not conduct continuously like a resistor would; instead, it allows the current to charge and discharge. This charging and discharging action happens in a cycle that corresponds to the frequency of the AC signal.

As the AC voltage rises, the capacitor accumulates charge until it's fully charged. When the voltage decreases, the capacitor returns energy back to the circuit, effectively releasing the stored charge. This ability to store and release energy is crucial for various applications, such as smoothing out the fluctuations in voltage (in power supplies) and tuning circuits in radio transmitters and receivers.

The other options provided do not accurately describe the function of a capacitor in AC circuits. For example, while a capacitor can influence impedance, its primary role is energy storage and release rather than increasing impedance outright or converting AC to DC. It does not act as a resistor; instead, it has a reactance, which means it behaves differently in an AC circuit compared to a resistive element.