10 ALTERNATING CURRENTS 



tance. (e) The power consumed by the circuit. Draw a vector diagram for 

 the circuit. 



(a) / 



65 cycles. Ans. 



V0.3 X 0.000020 



(b) E = IR = 5 X 20 = 100 volts. Ans. 



(c) E L = 2ir/L7 = 6.28 X 65 X 0.3 X 5 = 612 volts. Ans. 



(d) EC = //(27T/C) = 612 volts. Ans. 



(e) P = El = 100 X 5 = 500 watts. Ans. 

 The vector diagram is shown in Fig. 38. 



It will be observed that the voltage across the inductance 

 and that across the capacitance are equal, each being 612 volts, 

 or more than six times the line voltage. 



It should be noted that the current is a maximum when a 

 series circuit is in resonance. 



21. Parallel Circuits. In practice, parallel circuits are more 

 common than series circuits, because of the extended use of the 

 multiple system of transmission and distribution. The solution 



FIG. 39. Alternating-current parallel circuit and vector diagram. 



of problems with two or more loads in parallel involves the find- 

 ing of the current in each branch of the circuit and the combining 

 of these currents vectorially to give the resultant current. 

 This is illustrated by the following example: 



A resistance of 10 ohms, an inductive reactance of 8 ohms and a conden- 

 sive reactance of 15 ohms are all connected in parallel across 120-volt, 

 6O-cycle mains, as shown in Fig. 39 (a), (a) Find the total current. (6) 

 Determine the circuit power-factor, (c) Determine the power. 



