GENERATING ELECTRICITY COMMERCIALLY 191 



used instead of one loop, a current may be generated con- 

 tinuously. This method of generating electric current is 

 called induction. 



The strength of a current in electromotive force set up 

 by induction depends upon: (1) the strength of the magnet, 

 (2) the number of turns of wire in the coil 

 or loop, and (3) the speed with which the 

 magnetic lines of force are cut, that is, 

 the speed at which the coil rotates. 



228. Direction of an Induced Current. FIG. 83. Magnetic 



The direction of an induced current de- , Field - Showing 



loop oi wire rotat- 

 pends upon two factors: (1) the direc- ing between the 



tion of the motion of the wire, and (2) 



the direction of the magnetic lines of force. a magnet. 



A very valuable method of determining the direction of 

 current used in practical life is called Fleming's Rule. 



Place the thumb, forefinger, and center finger of the right 

 hand so as to form right angles to each other. If the thumb 

 points in the direction of the motion of the wire, and the fore- 

 finger in the direction of the magnetic lines of force, the center 

 finger will point in the direction of the induced current. 



It is very important to know the direction of the current 

 in revolving a loop of wire between the poles of a magnet 

 in order to understand the working of a dynamo. 



Examine Fig. 83 and notice, the loop of wire between the poles 

 of the magnet. If the loop is rotated to the right, as indicated by 

 the arrow head, the wire XB moves down during the first half of 

 the revolution. According to Fleming's Rule, the current would be 

 directed from B to X. The wire YA would move up during the 

 first half of the revolution and the current flow from A to Y. As 

 the result of the first half of the revolution, the current would flow 

 in the direction A YBX. 



