ELECTROMOTIVE FORCE AND CURRENT. 



11 



the electromotive force generated in the armature will send 

 a current through the circuit. The strength of this current 

 will depend on the ratio between the armature voltage and 



FIG. 5. CONNECTIONS OF CONDUCTORS IN MULTIPOLAR ARMATURE. 



the resistance of the circuit. Since the armature voltage is a 

 constantly varying quantity, the current in the circuit will 

 undergo the same variations. 



E 



Thus at any instant f C = ^ 



Where C value of current, 



E voltage, 

 E resistance of circuit. 



Since the current will go through similar variations to 

 the voltage, it may be represented by a curve in the same way 

 as the voltage in Fig. 4. 



E.M.F. of Self-induction in a Winding. As in the case of 

 a continuous current flowing through a winding, a magnetic 

 field is produced by an alternating current. In the latter 

 case, however, an important difference is introduced owing 

 to the fact that the field must vary as rapidly as the current. 

 Consequently, an alternating current is always accompanied 

 by a rapidly changing field, instead of the steady one which 

 is produced by a direct current. The effect of the varying 

 field upon the circuit by which it is produced must next be 

 considered. 



Imagine a coil of wire through which an alternating 

 current is flowing. 



The number of lines of force which are produced within the 

 coil will be proportional to the amount of current flowing ; 

 consequently every variation in current produces a pro- 

 portionate change in the number of lines passing through 

 the coil. The formation of lines of force passing through 



fThe effect of self-induct ion is, of course, not considered in this example. 



