L6 



ALTERNATING URRENTS 



voltages, between two or more voltages, or between two or more 



currents, 



9A. Addition of Currents. Figure 12 shows two currents, 



having effective values of 8 and 12 amp. respectively, uniting 



to flow in a common wire. If these 

 two currents were direct currents, 

 then by KirchhofTs first law (see 

 Vol. I, page 77), the current 7 3 could 

 have only two possible numerical 



FIG. 12. Alternating currents values, 12 + 8 = 20 amp. if the two 



currents flow in the same direction 



/ l= 12 Amp 



7 2 =8 Amp 



meeting at a junction. 



and 12 8 = 4 amp. if they flow in opposite directions. 



If the two currents, Fig. 12, are alternating, their sum 7 3 may 

 be equal numerically to any value from 20 amp. to 4 amp., de- 

 pending on the phase relation existing between I\ and 7 2 . 



Fro. 13. Addition of two currents in phase. 



Figure 13 shows these two currents plotted in phase with each 

 other. Their sum 7 3 is found by adding their ordinates at each 

 instant. The resulting current obtained in this manner will be 



