Before starting this module, you should be able to: When you complete this module, you should be able to: 
  • Define inductive reactance.
  • Describe the effect that inductive reactance has upon the amount of current flowing in an AC circuit.

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  • Cite the equation for determining the value of inductive reactance, given the values of applied frequency and inductance.
  • Solve the equation, given two of the three variables.

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  The equation for calculating the amount of inductive reactance in an ac circuit is given by:    

    XL = 2pfL 

where:    

XL = inductive reactance ohms (W)  
f = frequency in hertz (Hz)  
L = inductance in henries (H) 

The equation, XL = 2pfL , demonstrates the relationship between inductive reactance (XL), the frequency (f) of the waveform applied to the circuit, and the value of the inductance (L).  

The amount of inductive reactance (XL) changes proportionally with the applied frequency (f): 

  • Increasing the value of f causes XL to increase. 
  • Decreasing the value of f causes XL to decrease.

 

The amount of inductive reactance (XL) changes proportionally with the value of inductance (L): 
 
 

  • Increasing the value of L causes XL to increase.   
  • Decreasing the value of L causes XL to decrease.

 

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lblexa.gif (1250 bytes) What is the value of inductive reactance for an 0.1 H coil that is operating at 1 kHz? 
 

Ans: 628 W

Use the basic equation: 

XL = 2pfL  

 

lblexa.gif (1250 bytes) What value inductor is required for producing an inductive reactance of 10 W at 1.8 kHz? 

Ans: 88.5 mH   
 

Use this form of the basic equation: 

L = XL / (2pf )    

 

lblexa.gif (1250 bytes) At what frequency will a 150 mH inductor have an inductive reactance of 150 W

Ans: 159 Hz

Use this form of the basic equation: 

f = XL / (2pL)  

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