PRINCIPLES OF ALTERNATING CURRENT 227 



The only reaction left to balance the impressed force is the 

 resistance reaction and this may require a very large current. 

 If an inductance, capacity and resistance are in series and 

 L and C are so related that 



1 



then 



T= E E 



~R' 



The drop across the inductance (equal to 2-ju/L/) may be 

 very large because / may be large. The same condition 

 holds with respect to the condenser. 



Condition for Resonance. When the frequency, induc- 

 tance and capacity of a circuit are so proportioned that 



2-ju/L = , the circuit is said to be in a condition of reso- 



nance ; the circuit is resonant. This condition obtains when 

 l or 



The value of / obtained by solving this equation for 

 any circuit is said to be the critical or resonant frequency 

 for the circuit. 



Example oj a Resonant Circuit. Suppose we have an 

 inductance of 0.1 henry, a capacity of 70.4 micro farads and 

 a resistance of 2 ohms connected in series to a 60-cycle, 

 110-volt line. How much current will flow and what will 

 be the voltage across each part of the circuit? 



55 amperes. 



V2 2 + (S7.7-37.7) 2 



