What's the difference between reactance and resistance?

Resistance dissipates energy as heat, while reactance stores energy in magnetic (or electric) fields and returns it to the circuit. Resistance is frequency-independent; reactance increases with frequency.

Why does inductance increase with frequency?

Inductive reactance X_L = 2πfL shows direct proportionality to frequency. At higher frequencies, the inductor opposes current change more strongly because dI/dt is greater for the same voltage.

What's the reactance at DC (0 Hz)?

At DC, X_L = 2π(0)L = 0 ohms. Inductors have no reactance to steady-state DC—they appear as short circuits (just wire resistance). Reactance only matters for AC or transient signals.

How is reactance different from impedance?

Impedance (Z) is the total opposition including both reactance and resistance: Z = √(R² + X_L²). Reactance is just the AC opposition from the inductor; impedance combines it with resistive effects.

Does 2π have special meaning in this formula?

Yes! 2π converts angular frequency (radians/second, ω = 2πf) into the standard Euler form of AC analysis. The formula comes from L(dI/dt) and sinusoidal AC current relationships.

How is reactance used in filter design?

By calculating reactance at target frequencies, engineers design filters that block high frequencies (reactance increases) while passing low frequencies (reactance decreases). Essential for radio tuning and noise filtering.

What happens at inductor resonance frequency?

At resonance (X_L = X_C in LC circuits), the inductor and capacitor reactances cancel, leaving only resistance. This creates peak current flow and is used in radio tuning and power factor correction.

Can reactance be negative?

No, inductive reactance is always positive (X_L ≥ 0). Capacitive reactance is negative by convention. Total reactance in LC circuits (X_total = X_L - X_C) can be positive or negative depending on which dominates.