MAGNETISM AND ELECTROMAGNETICS 



59 



The m.m.f. of one ampere in one turn or one ampere turn is 

 0.4 TT gilberts. 



In studying the characteristics of electrical machinery it is 

 more convenient to use the ampere turn as the unit of m.m.f. 









FIG. 48. 



Unit Pole 



Magnetomotive force of a Solenoid. 



Thus the m.m.f. of a field coil of n turns carrying a current 7 



amperes is specified as nl ampere turns instead of 0.4 irnl gilberts. 



46. Examples. (1) The solenoid in Fig. 49 has nl ampere 



FIG. 49. Ring solenoid. 



turns and is wound in the form of a ring. The m.m.f. of the 

 solenoid is M = 0.4 irnl gilberts. 



If I cm. is the mean length of the path and A sq. cm. is the 

 sectional area of the path, the reluctance is 



