What happens to the voltage across a capacitor in an AC circuit?

In an AC circuit, the behavior of the voltage across a capacitor is characterized by its phase relationship with the current. Specifically, the voltage across a capacitor leads the current flowing through it by a phase angle of 90 degrees. This means that while the current is reaching its maximum and minimum values, the voltage across the capacitor reaches its maximum and minimum values a quarter cycle earlier.

This leading behavior occurs because a capacitor stores energy in the electric field created by the separation of charges. When an alternating current flows through it, the capacitor charges and discharges in sync with the AC waveform, but due to its inherent properties, the maximum voltage across the capacitor is established before the maximum current flows through it.

The other options do not accurately describe the behavior of voltage in relation to AC currents in capacitors. The voltage does not remain constant as it varies with the AC signal. Furthermore, the voltage does not lag the current, as that is characteristic of inductors. Lastly, the voltage across a capacitor does not fluctuate randomly; it follows the sinusoidal nature of the AC input.