Share:
How It Works
Reactance is the opposition to AC current caused by inductors and capacitors. Unlike resistance, reactance changes with frequency. Inductive reactance (Xₗ = 2πfL) rises with frequency, while capacitive reactance (Xᴄ = 1/2πfC) falls. This calculator solves either equation for any unknown variable.
The results are measured in ohms, the same unit as resistance. Together, resistance and reactance combine into impedance: Z = √(R² + X²).
Example Problem
A 10 mH inductor operates in a 60 Hz power circuit. What is its inductive reactance?
- Convert inductance: L = 10 mH = 0.01 H
- Apply the formula: Xₗ = 2π × 60 × 0.01 = 3.77 Ω
For a 100 μF capacitor at the same 60 Hz: Xᴄ = 1/(2π × 60 × 0.0001) = 26.53 Ω.
Frequently Asked Questions
What is the difference between reactance and impedance?
Reactance is the opposition to AC current from inductors or capacitors alone. Impedance combines reactance with resistance into a single value: Z = √(R² + X²). In a purely reactive circuit with no resistance, impedance equals the absolute value of the reactance.
Why does inductive reactance increase with frequency?
An inductor opposes changes in current. At higher frequencies the current changes direction more often, so the inductor resists more strongly. At DC (0 Hz), an ideal inductor has zero reactance and behaves like a short circuit.
How do you calculate capacitive reactance at 1 kHz?
Use Xᴄ = 1/(2πfC). For a 10 μF capacitor at 1,000 Hz: Xᴄ = 1/(2π × 1000 × 0.00001) ≈ 15.92 Ω. Larger capacitors or higher frequencies yield lower reactance.
What is power factor correction?
Industrial motors draw inductive current that lags behind the voltage, wasting energy. Adding capacitors reduces the net reactance, bringing current and voltage closer in phase. This lowers the apparent power demand and can reduce electricity costs by 10–30%.
Related Calculators
- Ohm's Law Calculator — solve for voltage, current, resistance, or power in DC and AC circuits.
- Capacitor Design Calculator — calculate capacitance, charge, voltage, or stored energy.
- Inductor Design Calculator — find inductance, permeability, turns, area, or coil length.
- Passive Crossover Calculator — design crossover networks using capacitors and inductors.
- Resistance Converter — convert between ohms, kilohms, megohms, and other resistance units.
Reference: Tipler, Paul A. 1995. Physics For Scientists and Engineers. Worth Publishers. 3rd ed.