Ac Electricity
Impedance
Impedance is the total opposition to alternating current, combining resistance and reactance. In a series R-L-C circuit the reactances oppose each other, so the net reactance is X_L − X_C. The impedance magnitude is the square root of the resistance squared plus the net reactance squared. Impedance is measured in ohms and determines the current for a given AC voltage.
Impedance
Z = √(R² + (X_L − X_C)²)
Variables and units
| Symbol | Quantity | Unit |
|---|---|---|
| Z | Impedance magnitude | Ω |
| R | Resistance | Ω |
| X_L | Inductive reactance | Ω |
| X_C | Capacitive reactance | Ω |
Conditions of application
Series R-L-C circuit in sinusoidal steady state. This expression gives the impedance magnitude only; the phase angle requires the reactance sign and a full phasor calculation.
Worked example
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