216 ELECTRICAL MACHINERY 



It is seen that by transposing the terms in equation 

 (48) we get the equation 



= ..... (49) 



It may be seen from Fig. 129 that in such an inductive 

 circuit, 



OA IR R 



The reactance and impedance of a circuit are both meas- 

 ured in ohms, the same as resistance. This is really an 

 improper use of the unit but it is used throughout this 

 book because it is common practice. 



Example to Illustrate Inductance and Impedance. To 

 illustrate the idea of inductance and impedance let us 

 suppose a circuit has a resistance of 100 ohms and a self- 

 induction of 0.5 henry and that the frequency of the cur- 

 rent in the circuit is 60 cycles. What is the reactance of 

 the circuit and how much is the impedance? As the react- 

 ance (in ohms) is given by the equation X = 2^fL we have 



The impedance 



= V100 2 +188 2 

 = 213 ohms. 



If an e.m.f. of 110 volts is impressed on this circuit the 

 current which will flow is given by the equation 



7= ~ =2jo-=0.517 ampere. 



