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Illustration Graph: AC voltage and current at capacitor

Graph: AC voltage and current at capacitor
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If an AC voltage is applied to a capacitor with capacitance \(C\), the same AC voltage \(U_{\text C}(t)\) is applied to this capacitor. The AC current \( \class{red}{I_{\text C}}(t) \) through the capacitor is 90 degrees out of phase with respect to the voltage.

We say:

The current into the capacitor precedes the voltage by 90 degrees!

On the graph you can see that the current maximum occurred at an earlier time, if you go 90 degrees to the left. Further to the left means earlier in time!