Induction Motor l.-,c>- 



These values are plotted in Fii:urc 1. in the " cnkiilatea " 

 curve. 



Experiment (b). — Furtlier experiments of tlie same nature were 

 carried out by removing the armature from a series wound " Im- 

 misch " motor, and replacing it by a hollow topper cylinder with 

 an iron core. The pole pieces were built up with cast iron so as 

 to clear the copper by about one millimetre. The whole wa» 

 mounted on a cradle dynamometer, and arranged so that the copper 

 cylinder could be rotated at different speeds by means «.f a Ix'lt 

 and pulleys of different sizes. 



Current was passed through the field coils and tliu torque pro- 

 duced on rotating the copper measured in the usual way. 



The value of <^ was measured by making and breaking the cur- 

 rent in the field coils, and noting the deflection of a fluxmeter with 

 an exploring coil, wound around the copper. In each case the 

 couple with zero flux was measured to eliminate the frictional 

 couple. The following results were obtained : — 



_. , . . voiiio r,f Mass of Distance of Couple due to Couple forrected 



Revolution ^ alue of ,,,,,^,,,.4, rider from Eddv , to 



per second. 2(fi ^jer. Centre. Currents. 9 = 2-79xl0»/2 



fifi^ 100 29 cm. ) 7±'j^U)^ 7 84xl0« 



^•^^ 2.72 xlO« 200 52.5 cm.) '•'^'^^l^' /.«4xl0 



^^ r^ ^ 1^0 IQcm. ) ^()Hv^O^ 119>ll)T 



1^:^ 2.74 X 105 200 60 cm. ) ^"^^^^^ ^•^-'^'^ 



16 1 ^ ^^ i*^"'- ' 1.23x10^ 1.23x10^ 



^^•^ 2.79x10-^ 200 70 cm. ) 



20.2 

 24.0 



100 16 cm. \ 127x10^ 1.27 xlO' 



2.79x305 200 73 cm. ) 



100 10 cm. I 127x10^ 1.27 xlo^ 



2.79x105 200 70 cm. , 



In order to correct the observed couples for variations in the value 

 of <f> it was assumed that the couple is proportioned to <^^ To verify 

 this, two experiments were carried out at the same rate of rotation 

 with values of <f> in the ratio of 1 to 2. The couples were measured a.s 

 before. The values of the ratio Couple :<^2 were found to \ye 

 6.07x10" and 6.04 xlO\ 



This justifies the assumption made. 



The values of the couples corrected in this way are given in the 

 last column of the table, and are plotted against revolutions per 

 second in Fig. 2. 



