Voltage lags current by 90° in a capacitor. Mathematically, we say that the phase angle of a capacitor’s opposition to current is -90°, meaning that a capacitor’s opposition to current is a negative imaginary quantity. (See figure above.)
Capacitors have the opposite effect on AC circuits that inductors have. Just as a reminder, consider Figure, which shows an AC voltage applied to a resistor and a graph of voltage and current versus time. The voltage and current are exactly in phase in a resistor. There is no frequency dependence to the behavior of plain resistance in a circuit:
From the following phasor diagram, we can see that current leads voltage by 90 degrees for a capacitor: Now that we have developed an understanding of the voltage-current relationship for resistors, inductors and capacitors (in the frequency domain), we will next look at the concepts of impedance and admittance.
Such a situation would involve physical damage to the capacitor and likely to the circuit involved as well. Since the voltage across a capacitor is proportional to the integral of the current, as shown above, with sine waves in AC or signal circuits this results in a phase difference of 90 degrees, the current leading the voltage phase angle.
Throughout the cycle, the voltage follows what the current is doing by one-fourth of a cycle: When a sinusoidal voltage is applied to a capacitor, the voltage follows the current by one-fourth of a cycle, or by a phase angle. The capacitor is affecting the current, having the ability to stop it altogether when fully charged.
Series capacitor circuit: voltage lags current by 0o to 90o. The resistor will offer 5 Ω of resistance to AC current regardless of frequency, while the capacitor will offer 26.5258 Ω of reactance to AC current at 60 Hz.