Practice portal › Alternating Current › Resonance in Series LCR
Asked in GUJCET 2025 · Resonance condition and tuning
Idea: resonance needs both an inductor and a capacitor, because it is the cancellation X_L=X_C that removes the reactance.
In a series LCR circuit that happens at ω₀=1/(√LC), where the impedance falls to its minimum, Z=R.
The phase angle is then zero, so cos φ=R/Z=1 and the circuit draws the greatest power it can.
A C–R or L–R circuit carries only one kind of reactance, so cos φ<1 at every frequency, and a pure inductor gives cos φ=0.
So the power factor is 1 at resonance only in the LCR series circuit.
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