Question 1

How do I calculate impedance from frequency, R, L and C?

Accepted Answer

For a series RLC circuit, first find the reactances Xl = 2πfL and Xc = 1/(2πfC). The impedance magnitude is |Z| = √(R² + (Xl − Xc)²) and the phase angle is φ = atan2(Xl − Xc, R). For example at 1 kHz with R = 50 Ω, L = 10 mH and C = 1 µF, Xl = 62.83 Ω, Xc = 159.15 Ω and |Z| ≈ 108.5 Ω at a phase of −62.6°.

Question 2

What is the difference between capacitive and inductive reactance?

Accepted Answer

Inductive reactance Xl = 2πfL rises with frequency, while capacitive reactance Xc = 1/(2πfC) falls with frequency. In a series circuit they subtract: the net reactance is Xl − Xc. When Xl is larger the circuit looks inductive (positive phase); when Xc is larger it looks capacitive (negative phase).

Question 3

What does the phase angle of impedance mean?

Accepted Answer

The phase angle φ is the angle between voltage and current. A positive φ means current lags voltage and the load is net inductive; a negative φ means current leads and the load is net capacitive; φ = 0 means purely resistive. It is computed as φ = atan2(Xl − Xc, R) in degrees.

Question 4

What is the resonant frequency of an RLC circuit?

Accepted Answer

Resonance occurs where Xl equals Xc, at f0 = 1/(2π√(LC)). At that frequency the reactances cancel, so in a series RLC circuit the impedance drops to just R and the phase angle is zero. For L = 10 mH and C = 1 µF, f0 ≈ 1591.5 Hz.

Question 5

Does this calculator account for parasitics and ESR?

Accepted Answer

No. It assumes ideal series-connected elements driven by a steady sinusoid. Real components have equivalent series resistance (ESR), parasitic inductance and capacitance, tolerance and temperature drift, and at high frequency distributed effects matter. Treat the result as a first-order estimate, not a measured value. Parallel topologies need a different formula.

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