Calculate the resonant frequency of an LC (Inductor-Capacitor) circuit.
Last updated: March 2026 | By ForgeCalc Engineering
Resonant frequency is the natural frequency at which a system tends to oscillate with maximum amplitude. In an LC circuit, it is the frequency at which the inductive reactance (X_L) and capacitive reactance (X_C) are equal in magnitude but opposite in phase, canceling each other out.
At this frequency, the circuit's impedance is at its minimum (for a series LC circuit) or maximum (for a parallel LC circuit). This principle is the foundation of radio tuning, filters, and oscillators.
Where:
• f₀ is the resonant frequency in Hertz
• L is the inductance in Henrys
• C is the capacitance in Farads
A radio uses a variable capacitor or inductor to change its resonant frequency. When the circuit's resonant frequency matches the frequency of a broadcast station, the signal is amplified and selected.
The Q (Quality) factor describes how 'sharp' the resonance is. A high Q factor means the circuit is very selective and has low energy loss (resistance).
In an ideal LC circuit, no. However, in a real RLC circuit, resistance slightly lowers the resonant frequency and dampens the oscillation.
Real-world components like inductors have parasitic capacitance. The frequency at which an inductor resonates with its own internal capacitance is its self-resonant frequency (SRF).
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