ELECTRIC CIRCUITS 143 



Substituting the values above 



.E 



= i Xi, since 



or in absolute values 



and 7 = . 



zi 



Since #1 is constant 7 is constant independent of the impedance 

 and the power factor of the receiver circuit. This circuit there- 

 fore transforms power from constant potential to constant cur- 

 rent. 



87. Kirchoff's Laws Applied to Alternating-current Circuits. 

 Kirchoff's two laws enunciated in Art. 60 apply directly to al- 

 ternating-current circuits when dealing with instantaneous values 

 of e.m.f.'s and currents; they also apply to the effective values of 

 e.m.f.'s and currents when combined in their proper phase rela- 

 tions. Thus the vector sum of all the e.m.f.'s around a closed cir- 

 cuit is zero if the e.m.f. consumed by resistance is considered as a 

 counter e.m.f. in phase opposition to the current; and the vector 

 sum of all currents at a distributing point is zero. 



