108 



ELECTRICAL ENGINEERING 



where X c = 



is called the condensive reactance of the circuit 



27T/C 



and is expressed in ohms. 



In Fig. 77 curve 1 represents the impressed e.m.f. e E 



FIG. 77. Capacity in alternating current circuits. 



sm2irft and curve 2 the current i = 7 sin (2 irft + 90). Be- 

 tween the points a and 6 the current is positive and the e.m.f. is 

 increasing; from b to c the current is negative and the e.m.f. is 

 decreasing. 



$ WA/W 



R 



T 



Curve <D.e R =tRX~^\ UrVe e=i 



FIG. 78. Resistance and condensive reactance in series. 



77. Resistance and Condensive Reactance in Series. If an 

 alternating current i = IQ sin 2 irft flows in a circuit consisting 

 of a resistance E in series with a condenser of capacity C farads 



and reactance of X e = ^ ^ ohms, determine the magnitude of 



