i6 



ALTERNATING CURRENTS 



termed the power factor of the circuit. In the case considered, the 

 power-factor is cos 9, but the term " power factor " is used generally, 

 even in connection with circuits in which the waves are no longer of 



the simple sine form, to express the ratio = 2 . 



volt-amperes 



The expression for the mean power may be written in the form 



E I 

 ^ -fit cos 9. Now I cos 9 is the projection of the current vector 



on the impressed e.m.f. vector, and since the power depends on the 

 magnitude of this projection, we speak of ^ cos 9 (i.e. r.ni.s. current 

 X cos 9} as the power component or load component of the current, 

 while -JT sin 9 is termed the idle or wattless component of the current. 



It is frequently convenient to regard the current in a circuit as split 

 up into these two components, as shown in Fig. 11, where the vectors 

 are taken to represent r.m.s. values of the current. 



POWER COMPONENT 

 Of CURRENT 



CURRENT 



AT LESS COMPONENT 

 OF CURRENT 



FIG. 11. Decomposition of Current into Power and Wattless Components. 



