Condensator in een AC-circuit

Consider a capacitor connected across an alternating current voltage source. Recalling Kirchhoff's loop rule, the instantaneous voltage across and the charge on the capacitor can be determined.

The rate at which charge enters or exits the capacitor is equivalent to the current flowing through the circuit, and the trigonometric relationship can be used to determine the instantaneous current.

When voltage and current are plotted together, the current through the capacitor leads the voltage across the capacitor by a quarter of a cycle.

The relationship between instantaneous current and voltage can be represented using phasor diagrams, where both phasors rotate at the same angular frequency, with the current phasor leading the voltage phasor by π by 2 radians.

The ratio of peak voltage to peak current gives the capacitive reactance of the capacitor, expressed in ohms.

The capacitive reactance of the capacitor depends inversely on the frequency of the alternating current source, where a high frequency leads to a low capacitive reactance and vice versa.