80 Inductance, Resistance, and Self-Capacity of Magnetos. 



The difference in capacity C — Ci should be small, so that 

 B. e and L e do not change appreciably, and the maximum 

 current should be the same in each case. The frequency 

 corresponding to the values of L e and E e may be taken as- 

 (/o+/i)/2, i.e. the mean of the two frequencies*. 



It is not suggested that either of the methods outlined 

 will give particularly accurate results. They will at least 

 indicate the order of magnitude. In measuring inductances 

 and resistances of iron-cored coils, the conditions are 

 invariably complex, especially at low frequencies where 

 the apparent permeability is susceptible to pronounced 

 variation, and also at high frequencies if the magnetizing* 

 forces are large. More accurate results could probably 

 be obtained by using the method shown in fig. 23. Damped 



Fig. 23. — Diagram of apparatus used for bridge method of determining 

 self- inductance and effective resistance under damped oscillations. 



Battery ^^tat. 



r ji|i|iJW I 



Contact I 

 Breaker^ 



mm- 



'■—^Pft^A^j. 



Iron Cored 

 Differential 

 \ Transformer 



^J>e 



oscillations are obtained using a battery and a contact- 

 breaker. B, and L are adjusted to obtain a balance. 

 Then R = K e and L = L e , and the frequency of the system 

 is given by 



, / 2 R 2 \ 



By varying 0, different frequencies can be obtained. If 

 the detector is selective, the effect of harmonics can be 

 examined. In place of the battery and condenser, a source 

 of undamped waves can be used to determine E e and L e 

 instead of the methods used herein, as has been stated 

 before. 



November 1919. 



