In a purely capacitive circuit, how does the current relate to the voltage?

In a purely capacitive circuit, the relationship between current and voltage is characterized by the phase difference, which is crucial for understanding AC circuits. In this case, the current leads the voltage by 90 degrees.

This phenomenon occurs due to the nature of capacitors, which store electric charge. When an alternating current flows through a capacitor, the voltage across the capacitor does not immediately rise as the current flows into it. Instead, the current reaches its maximum value first, as it charges the capacitor, while the voltage across the capacitor rises more slowly. This results in the current leading the voltage waveform.

As a result, in a purely capacitive circuit, when you analyze the phase angles, the current waveform reaches its peak a quarter cycle (90 degrees) ahead of the voltage waveform. This phase relationship is essential in the analysis of reactive components in AC circuits and affects how power is consumed and transferred.

Understanding this lead of current over voltage is foundational for electrical engineering and practical applications of AC circuit design.