38 Dr. MeLachlan on Effective Inductance, Effective 



in quadrature, as shown in fig. 1 . These represent, respec- 

 tively, the ohmic drop due to the effective resistance caused 



Fig. 1.— Vector diagram illustrating definition of effective inductance 

 and effective resistance. 



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Pel 



chiefly by iron loss but also by dielectric loss and eddies in- 

 metal fittings, and the drop due to the effective inductance. 



The apparatus used is shown diagram ma tically in fig. 2^ 

 A triode is employed to generate oscillations in circuit (1).. 



Fig. 2. — Diagrammatic arrangement of apparatus used to determine 

 the primary inductance and effective resistance 



Valve Generator 



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Primary of Magneto 



A second circuit contains an inductance coupled to the 

 inductance in circuit (1), a variable condenser, variable 

 inductance, and the primary of the magneto under test. 

 It is necessary to -remove the secondary winding and to 

 arrange that the total inductance in circuit 2 (apart from 

 that of the magneto) is as small as convenient. This is 

 essential so that a small change in inductance will produce 

 a perceptible change in the current measured on the Duddell 

 milliammeter A, since the high effective resistance of the 

 magneto causes the resonance curve to be rather flat-topped. 

 The variable inductance is adjusted so that circuit (2) is 

 brought into resonance. The resonance point is found by 

 obtaining the inductances on either side of the maximum 

 current for which the current has equal values. The- 



