38 



ALTERNATING CURRENTS 



' 96.8 V. 



ER = 85.5 V. 



^=96.8 V 



7=1.71 a 



Figure 37 gives the vector diagram for the circuit conditions 



represented by this problem. 



It will be observed that the voltage across the condenser 



exceeds the line voltage by a considerable amount. This would 



be impossible under like con- 

 ditions in a direct-current 

 circuit, for the voltage across 

 any part of the circuit cannot 

 exceed the line voltage. This 

 condition can exist in an 

 alternating-current circuit, be- 

 cause the condenser voltage 

 and the inductance voltage 

 are in direct opposition. 

 Both may be large, provided 

 their difference is less than 

 the line voltage. 



20. Resonance in a Series 

 Circuit. The general equa- 

 tion (22) for the current in a 

 series circuit shows that for 

 fixed values of resistance and 



c 181.1 V.) 



FIG. 37. Vector diagram for series 

 circuit, giving numerical values. 



impressed voltage the current is a maximum when the expression 

 in the parenthesis under the square root sign is equal to zero. 

 That is, in the equation 



the current is a maximum when 



and then becomes 



its Ohm's law value. 

 Under these conditions 



and 



E 



E 



VR* + (o) R 



2irfL = 

 27T/L7 = 



1 



27T/C 



/ 



27T/C 



(25) 



