60 Dr. McLachlan on Effective Inductance, Effective 



Finally, if all the primary energy at break were trans- 

 ferred to the secondary in the form iC 2 V 2 2 j the peak voltage 

 would be 21,300. 



(9) Comparison of foregoing methods of calculating Loss. 



We are now in a position to compare the values of the. 

 loss in a' magneto obtained by the two methods of com- 

 putation. The first method yields 3*1 X 10~ 3 joule and the 

 second 1*6 x 10 -3 joule. It is evident, therefore, that one or 

 both of the methods or the assumed frequency is in error. 

 It is possible of course to select a frequency for lohich the 

 methods yield identical results. 



In the experiment with the short-circuited exploring coil 

 (see 6 d) it was shown that the effective resistance of the 

 primary winding was decreased owing to mutual action. Now 

 in a magneto under working conditions there is a mutual 

 action between the primary and secondary currents. The 

 oscillations of lower frequency are almost in phase, whereas 

 those of higher frequency are almost in opposition. Thus 

 the magnetization will be increased in the fust case but 

 decreased in the second. This affects the effective resist- 

 ances accordingly, and introduces an indefiniteness with 

 regard to their magnitude under working conditions. It 

 appears, therefore, that without a knowledge of the precise 

 conditions, the data obtained in the experiments is not of 

 much value in the prediction of the loss. Owing to the 

 variation with frequency the requisite values for substitution 

 in expression (10) are unknown and can only be assumed. 

 Hence on this basis both methods of computation are 

 unreliable. 



The interaction of primary and secondary suggests a 

 third way in which the problem of ascertaining the loss 

 can be attacked. The effective resistance of the primary 

 is found by current variation as before, but with the 

 secondary winding in position. In this way the reaction* 

 of the secondary is obtained. The results are exhibited 

 in fig. 17, which has the same appearance as the usual 

 type of resonance carve. This curve may be termed a 

 resistance-resonance curve, since the peak value of the 

 resistance occurs at approximately the same frequency as 

 that at which the secondary coil has its first self-resonance. 

 If the mean frequency of the oscillations in the magneto is 

 assumed, we can calculate the total primary and secondary 



* The reaction under clamped oscillations is different from that obtained 

 with undamped oscillations. 



