142 ELECTRICAL ENGINEERING 



The power factor of the circuit is 



The vector diagram is drawn with E z as the axis. 



(4) If an e.m.f . E = 14 + j 38 is impressed on a circuit and a 

 current I = 6 + j 2 flows, find the impedance of the circuit. 



The impedance is 



14+J38 6-J2 

 6+J2 X 6-j2 



_ 160+1200 = 



the resistance of the circuit is 4 ohms and the inductive reactance 

 is 5 ohms. 



(5) In Fig. 108 a condensive reactance x e is connected across 

 the terminals of a receiver circuit of variable impedance z = r -f 



FIG. 108. Constant potential to constant current. 



jx. If an inductive reactance x\ = x c is connected in the supply 

 lines and a constant e.m.f. E\ is impressed on the terminals, show 

 that the current in the receiver circuit is constant independent 

 of the impedance and power factor. 



E = e.m.f. at terminals of receiver, 



ET 



I = = current in receiver, 



E 



I c = '-r = current in condensive reactance, 

 -jx c 



1 1 = I + I c = current in the line, 

 EI = E -\-jIiXi = e.m.f. impressed. 



