TRANSFORMATION OF CHARACTERISTICS. 



729 



1276. TRANSFORMATION OF CHARACTERISTICS. When the 

 characteristic has been found for a machine, we may, by a simple 

 geometrical construction, deduce from it the curve which would 

 hold for the same machine, the wires of which had been changed, 

 while retaining the same total volume and the same mode of 

 winding. 



In fact, for the inductor, the field of the current which traverses 

 the wires is proportional to the number of turns, and to the intensity 

 of the current. The field will then be the same, and therefore the 

 magnetisation will not be modified, if we replace the number of 

 turns N by N', on condition that the new intensity I' satisfies the 

 equation 



NI = NT. 



The original value of E x for the current I is then the same in the 

 new machine for the current 



and the characteristic curve EJ of the new machine will be deduced 

 from the characteristic curve Ej relative to the former, if we take for 

 the same ordinate MP (Fig. 260), abscissae C'P' and CP, which are 

 in the ratio of N to N'. 



In like manner, if the iron ring is not altered, and we replace the 

 number of turns P by another number P' of turns occupying the 

 same volume, the corresponding characteristic functions are in the 

 ratio of P to P'. 



1277. DISTRIBUTION OF ENERGY. It is often necessary to use 

 fractions of the current of an electromotor for instance, in lighting 



