.1 MAGXETIC CURVE TRACIili 

 Combining this with Eq. (3), we have 



A//, = Xi 



(IH 



dt 



29 



(4) 



Data taken with no magnetic specimen inserted show that this Hnear 

 relation actually exists. Added to this there is an increase in II ^ due to 



Fig. 10 — A diagram to illustrate the widening of a loop due to inductance. 



eddy current lag. Johnson ^ has derived an equation for this, and with 

 a slight modification to make it applicable to cylindrical specimens, it 

 is: 



nio-3 ,dBdH 

 2 p dtl di 



(5) 



where p is the resistivity of the specimen, and r its radius. This gives 

 us for the total error. 



Mh = Xi + 



n 10-9 ^dB\dII 



2 <.■ ' dllj dt 



= (Xi + X.) 



clU 



dt 



This equation was tested experimentally by taking a series of loops 



