

DETERMINATION OF WAVE FORM 627 



In the case under consideration, the flux through the core is 



( \ 



Mt 



Or if V 2 is in volts, 



If a non-synchronous commutator is used, the maximum value 

 of the flux will be proportional to the maximum reading of the 

 voltmeter, as it goes through its cycle of deflections. 



Use of Condenser and Synchronous Commutator. Another 

 arrangement for determining the forms of potential waves is 



Fio. 391. Connections for determining wave form by synchronous com- 

 mutator and condenser. 



shown in Fig. 391. Here a condenser, the commutator and a 

 galvanometer, or a millivoltmeter, are joined in series across 

 the mains. 



da 

 The current through the circuit is i = -r;. In half a cycle 



the charge on the condenser changes from +q to q } so 



+ 2 



r~ q C t+ 



\"dq-"\ idt 



J +Q Jt 



The reading of the galvanometer, 7, is proportional to the average 

 current, or /* + - f*t+ - 



idt = 2f I idt 



But if a good condenser is used, q = V t C, 

 so I 



