ELECTRIC CIRCUITS 



115 



Tjil T 



The maximum value of power is - - (1 + cos<), which is less 



a 



than in Case I, and the power curve falls below the base twice in 



-P 



FIG. 82. Power in an inductive circuit. 



each cycle. The energy consumed per cycle is the difference 

 between the positive and negative areas intercepted by the power 

 curve. 

 The average power is 



P = - 



= ?****- cos (2 - 0)1 



^|7r.cos0- 



^ 7T 



sin ( 0) sin ( </>) 



O I o 



= E7cos0; (173) 



therefore, the average power is the product of the effective values 

 of the e.m.f . and current multiplied by the cosine of the angle of 

 phase difference between them. 



From the vector diagram, in Fig. 82, it is seen that 



E cos <j> = Ei = IR, 

 and therefore the power is 



p = EJ = PR, 



