MAGNETIC LOSSES AT LOW FLUX DENSITIES 



225 



computed using the value of e obtained from the resistance measure- 

 ments in the relation 



L _ 1 sinh d + sin 6 

 Lo 6 cosh 6 -\- cos d 



^ 30 "^ 732 



where d = V3gMo//7r. Using the values of L/Lo thus computed, the 

 effect of eddy current shielding was eliminated from the observed values, 

 and the results plotted in the upper curve in Fig. 8, showing a rapid 



J=-0.90 



1000 2000 3000 4000 5000 6000 7000 8000 9000 10,000 11,000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 8 — L/Lo from intercepts of F~ig. 7. Observed values about 1 per cent lower than 

 calculated for eddy -current shielding. 



decline of inductance or apparent permeability with increasing fre- 

 quency at low frequencies, and the flattening off to a fairly constant 

 value at higher frequencies. 



The initial permeability thus obtained (average of results from the 

 20-turn and 60-turn windings) is 1780. This is somewhat lower than 

 the value found by the ballistic galvanometer. The difference is due 

 to magnetic aging which was observed to decrease the permeability of 



* The series is inaccurate at frequencies above 5000 cycles. 



