.\LTKH\.\ TING-CURRENT 



39 



That is, tho voltage across the inductance is equal to the 

 voltage across the capacitance. As these two voltages are in 

 exact opposition, they balance each other, so that the IR drop is 

 equal to the lino voltage. This is illustrated in Fig. 38. 



When the foregoing conditions exist, the circuit is said to be in 

 resonance. The current is then in phase with the line voltage 

 and the power P = El. 



Solving equation (25) for the frequency 



27T/L - 



1 



27T/C 



/ 







(26) 



This is the frequency for which a circuit having fixed values of 

 L and C will be in resonance. It is sometimes called the natural 

 frequency of the circuit, because it is 

 the frequency at which the current in 

 the circuit will oscillate, if no external 

 frequency is impressed on the circuit, 

 provided the resistance R is less than 

 \ 1/,/C. For example, in a radio 

 circuit a condenser C, charged to a 

 high voltage, is discharged into an E , 



27T/L/- 



612V. 



1 



2T/C 



/-5.0a 



inductance L, of negligible resistance. /-ioov. 

 The frequency of the resulting 

 oscillations as determined by the 

 values of L and C, is given in equa- 



26 . 



As the voltage across the inductance 

 equals the voltage across the capaci- 

 tance-, when the circuit is in i 

 nance, and t he t wo are in opposition, 

 c;ich may reach a high value, even 



with moderate line voltage. This is illustrated by the t'ollow- 

 \ample. 



't has a resist." n induct 



1 H hat VIlllH- of tlir frec|uen. 



unp. find the line voltage. 

 It age across the inductance, (d) The voltage across the capaci- 



612V. 



liauram for 

 circuit in rr-0! 



