ITS 



THE MAGNETIC CIRCUIT 



[ART. 56 



while the amount (Ee)idt='PRdt is converted into 



beat 



If now the same resistance is suddenly introduced into 

 the circuit, the current gradually returns to its former value, and 

 ilurini: this variable period the i 2 R loss is larger than the power Ei 

 supplied by the source. The applied voltage is in this case assisted 

 by the voltage e induced by the decreasing field, the e.m.f. e sup- 

 plying part of the &R loss. 



To make the matter more concrete let the source of electric 

 energy be a constant-voltage, direct-current generator, driven by 



FIG. 45. The magnetic field produced by a coil, showing complete and 



partial linkages. 



a steam turbine. Let the load consist of coils of variable resist- 

 ance /*, and let the coils produce a considerable magnetic field. 

 As long as the load current is constant, the rate of the steam con- 

 sumption is determined by the i 2 R loss in the circuit. When the 

 current increases, the steam is consumed at each instant at a 

 higher rate than it would be with a constant current of the same 

 instantaneous value. The energy of steam is thus partly stored 

 in the magnetic field of the coils. When the current is returned 

 to its former value, the steam consumption during the transitional 



