MAGNET STEELS AND PERMANENT MAGNETS 



387 



Following the permeameter measurements, each bar was magne- 

 tized as a straight bar magnet in an air core solenoid. Field strengths 

 of over 1 ,000 oersteds were applied to each bar. Upon removal from 

 the solenoid the flux density at the middle of the bar was measured 

 by means of a search coil and the Grassot fluxmeter with lamp and 

 scale. It is the flux density measured in this way that is referred to 

 in this discussion as the remanence of a magnet, or Brem- 



After the measurements at 12-in. lengths were completed, each bar 

 was cut in succession to 10, 8, 6, 4, and 2-in. lengths by removing 

 1 inch of material from each end except that in the case of some of the 

 bars of larger cross-section the lengths of 10, 6, and 2 inches were 

 omitted. 



Remanence measurements were made at each of the above lengths. 



IIO-VOLT DC SUPPLY 



AMMETER 



GRASSOT FLUXMETER 



B-COIL OF J-PERMEAMETER 



MAGNETIZING COIL OF J-PERMEAMETER 

 PM mutual INDUCTANCE PRIMARY 

 S^, MUTUAL INDUCTANCE SECONDARY 



L 



A 



G 



Bj 



Mj 



Fig. 3 — Control circuit of the Babbitt perrneameter. Note that the connections are 



those of a simple ring test. 



The bars were remagnetized for each new measurement of Brem- 



The foregoing experiments made available for analysis a wide range 

 of values of the associated variables Br.m, Br, H,, length L, and cross- 

 sectional area A . 



Analysis of Data. The values of remanence versus length for a 

 number of the straight bar magnets are plotted in Fig. 4 to show the 

 range of values existing in different bar magnets of the same length, 

 when fully magnetized. The differences in Brem for a particular length 

 of bar are due to the differences in Br, He, and cross-section of the 

 various samples. 



The chief characteristic that the curves of Fig. 4 have in common is 

 a resemblance in shape to a normal induction curve and an asymptotic 

 approach to limiting values of Brem as the lengths increase. 



