Electrical · Free Calculator
LC Resonant Frequency Calculator
Find the frequency at which an inductor and capacitor resonate, or the component value needed to tune to a target frequency.
f = 1/(2π√LC)Find L or CFiltersHarmonic resonance
Resonant frequency503.29 Hz
Reactance at resonance3.162 Ω
How this result was calculated
- f = 1 ÷ (2π × √(0.001 × 1.000 × 10^−4)) = 503.29 Hz
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Resonant Frequency Formula
fr = 1 ÷ (2π × √(L × C))
Worked example
1 mH with 100 µF resonates at 1 ÷ (2π × √(0.001 × 0.0001)) = 503 Hz, close to the 10th harmonic of 50 Hz.
Key insight: power factor capacitors and the supply transformer inductance form a resonant circuit. If it lands near the 5th or 7th harmonic, VFD harmonics are amplified, which is why detuned reactors are used.
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Frequently Asked Questions
What happens at resonance?
Inductive and capacitive reactance are equal and cancel. A series LC circuit has minimum impedance; a parallel one has maximum impedance.
How is resonance used in electronics?
In filters, oscillators and radio tuning circuits, which select one frequency and reject others.
Why is resonance a problem in power systems?
It can amplify harmonic currents and voltages, overheating capacitors and tripping drives.
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