Suppose we have a series RLC circuit with equal impedances connected to a 50Hz 240Vrms AC. We use an oscilloscope to measure and compare the voltages across each component.

1) Are their "VOLTAGES" all in phase?

2) If not what "VOLTAGES" are out of phase with each other?

  • 2
    \$\begingroup\$ If the three elements are in series they all have the same current. Say the resistor is 1 ohm, capacitor -j, inductor +j. You can work out the voltages. \$\endgroup\$
    – sstobbe
    May 14, 2017 at 1:39

1 Answer 1


Suppose we have a series RLC circuit with equal impedances

The impedance of the capacitor cannot have the same impedance as the inductor - it can have the same magnitude of impedance but the impedance polarity is negative compared to an inductor.

So, assuming that is what you meant, those two impedances will cancel out leaving only the resistance (loss) across the power supply. This resistor determines the current that flows. That current is in phase with the supply voltage.

Across the capacitor and across the inductor are voltages that are 90 degrees to the current flow: -

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