68 



ELEMENTS OF ELECTRICAL ENGINEERING. 



as the line <0Q in Fig. 58), then the three parts of the total 

 electromotive force are represented by the lines RI, a>LI, and 

 I/a) C, respectively, as shown, and the total electromotive force is 

 represented by the line E which is the vector sum of RI, coLI, 

 and I/coC. Therefore, from the right triangle whose sides are 

 (RI), (coLI I/coC), and E, we have : 



or, using equations (5) and (6) of Art. 25, we have 



and 



a>L- 



tan 6 = 



coC 



R 



(8) 



(9) 



These two equations determine the effective value and phase 

 of the harmonic electromotive force required to maintain a given 



Fig. 59. 



harmonic current, or they determine the effective value and 

 phase of the harmonic current that is maintained by a given 

 harmonic electromotive force under the conditions represented in 

 Fig. 57- 



