AC circuit opposition
What is inductive reactance?
Inductive reactance is the opposition an inductor presents to alternating current because its magnetic field changes continuously.
Unlike ordinary resistance, ideal inductive reactance does not dissipate electrical energy as heat.
Main AC formula
Inductive reactance formula
Inductive reactanceXₗ = 2πfL
- Xₗ is inductive reactance in ohms.
- f is frequency in hertz.
- L is inductance in henries.
Worked example
Calculate inductive reactance
Suppose an inductor has an inductance of 0.2 H in a50 Hz AC circuit.
- Use Xₗ = 2πfL.
- Substitute f = 50 Hz and L = 0.2 H.
- Xₗ = 2 × π × 50 × 0.2.
- The inductive reactance is about 62.83 Ω.
Frequency relationship
How frequency affects reactance
Inductive reactance rises directly with frequency. An inductor therefore offers little opposition to very low-frequency current but greater opposition at higher frequencies.
AC versus DC
Inductors in DC circuits
At steady-state direct current, frequency is zero, so ideal inductive reactance is also zero.
A real inductor still has winding resistance and other non-ideal effects.
SI unit guidance
Reactance units
- Reactance: ohms (Ω).
- Frequency: hertz (Hz).
- Inductance: henries (H).
- Angular frequency: radians per second.
- 1 millihenry = 1 × 10⁻³ H.
- 1 microhenry = 1 × 10⁻⁶ H.
Practical applications
Where inductive reactance matters
- AC filters and crossover circuits.
- Transformers and motor windings.
- Radio-frequency inductors.
- Power-factor calculations.
- RLC circuit analysis.
Model limitations
Assumptions and limitations
- The inductor is treated as ideal.
- Winding resistance is ignored.
- Parasitic capacitance is not included.
- Core saturation and frequency losses are not modelled.
- Inductance is assumed constant.
Common questions
Inductive reactance calculator FAQ
What formula does the inductive reactance calculator use?
It uses Xₗ = 2πfL, where Xₗ is inductive reactance, f is frequency, and L is inductance.
What is the unit of inductive reactance?
Inductive reactance is measured in ohms, written Ω.
How does frequency affect inductive reactance?
Inductive reactance increases directly with frequency. Doubling frequency doubles reactance when inductance remains constant.
How do I calculate inductance from reactance?
Divide inductive reactance by two pi times frequency using L = Xₗ/(2πf).
Is inductive reactance the same as resistance?
No. Resistance dissipates energy, while ideal inductive reactance opposes alternating current through magnetic-field effects.