Electronic – Why does a capacitor create a 90 degree phase shift of voltage and current

capacitorphase shift

First look at my circuit. The voltage source has a value of 5V with a phase angle of zero, and the capacitor's impedance is 5Ω. So the current is obviously 1A with a phase angle of 90°.

Circuit Diagram

What is the physical reason behind this phase shift? I can prove mathematically that a capacitor can make a 90° leading phase shift. But I want to know the physical reason for it.

Best Answer

If, instead of a sine-wave, you consider a turning on the circuit for the first time, with a DC voltage source and a discharged capacitor.

Immediately after you turn on, the maximum current will be flowing, and the minimum voltage will be across the capacitor.

As you wait, the current will reduce as the capacitor charges up, but the voltage will increase.

As the voltage arrives at its maximum, the current will have reached minimum.

And that's basically it - that's a description of a pair of sine-waves (one voltage, one current), 90 degrees out of phase, with alternating mutually-exclusive minima and maxima.