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AC Components and Circuits
Inductive Reactance

Section 2-2 Inductive Reactance

I2-2 Inductive Reactance



Inductive Reactance

Inductive reactance is the opposition to AC current caused by the alternating flux lines of an inductor.



Inductive reactance is similar to resistance in the sense that it opposes current flow. One of the major differences, however, is that the value of inductive reactance changes with the applied frequency--resistor values do not.


Inductive Reactance

XL = 2pfL


XL = Inductive reactance in W
f = Frequency in Hz
L = Inductance in H


These graphs show how inductive reactance responds to changes in frequency and the value of the inductor, itself.

All other things being equal, the first diagram shows that XL rises in proportion to the frequency. In fact, reactance is zero when 0 Hz  (or DC power) is applied.

The  same is true when varying the value of inductance: the larger the value of the inductor, the greater amount of reactance to current.






More Examples

Endless Examples & Exercises

Given the value of an inductor and the frequency of the applied sinusoidal waveform,  calculate the amount of inductive reactance.


Variations of the XL Equation

Solve for the value of the inductor: L = 



This is a design situation where you need to select an inductor that will provide a known amount of reactance at a certain frequency.

Solve for the frequency: f = 







What value inductor is needed in a circuit that is to provide 1.2kW reactance at 240 kHz?

1. Select the appropriate equation:




2. Substitute the known values:



= 1.2x 103
2pf 6.28(240 x 103)

3. Complete the math:


1.2x 103 = 0.000796
6.28(240 x 103)

4. Present the solution:





David L. Heiserman, Editor

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Revised: June 06, 2015