HYSTERESIS LOSS. 103 



Expressing E in ergs per cubic centimetre per cycle we get 



Thus the loss due to eddy currents is seen to be proportional to 

 the square of the thickness of the iron stampings. 



Now the counter E.M.F. in the primary circuit is on open 

 secondary equal in volts to the product of the rate of change of the 

 flux and the number of primary turns divided by 10 8 . Thus the 

 counter E.M.F. is proportional to the product of the frequency and 

 the maximum induction ; that is, to nB. But the counter E.M.F. 

 is nearly equal to the primary applied P.D. on open secondary ; 

 therefore we may say approximately that the eddy current loss is 

 proportional also to the square of the applied potential difference, 

 and is constant so long as the applied P.D. remains the same, and 

 is independent of the frequency. Hence, also, if the applied P.D. 

 and the frequency are constant, so is the maximum induction, and 

 the maximum induction for a constant applied P.D. varies inversely 

 as the frequency. 



HYSTERESIS Loss. 



62. We have already seen (see 59) that the average rate of 

 loss of energy due to hysteresis is given by 



E' = knS a watts 



where a is a constant which lies between 1/4 to 1*6, according to 

 the quality of the iron, and k is also a constant for a given quality 

 of iron, and has values given, according to Steinmetz, by the 

 following table : 



TABLE III. 



HYSTERETIC CONSTANTS FOB DIFFERENT MATERIALS. 



