FACULTY OF APPLIED SCIENCE. 



ELEMENTARY LAWS OF CONTINUOUS CURRENTS 25 



thus: a conductor so moved through a magnetic field that it 

 cuts lines of force will have induced in it an electromotive 

 force. As stated in section 10 the magnitude of this 

 e.m.f. depends upon the rate at which the lines of the 

 magnetic field are cut. 



An electric generator, then, is a device for producing 

 a magnetic field, in some manner or other, and having 

 conductors so arranged that they may be moved through 

 this magnetic field. Ordinarily the magnetic field is pro- 

 duced by a set of electromagnets and the conductors, in 

 which the e.m.f. is to be generated, are placed on the per- 

 iphery of a part of the magnetic circuit called the armature 

 core, which is capable of rotation. When the armature 

 core rotates, the conductors, which of course turn with it, 

 are carried through the magnetic field produced by the 

 electromagnets. 



Principle of the Motor. The principle underlying the 

 action of the motor may be stated thus : // current is passed 

 through a conductor which is placed in a magnetic field (but 

 not so placed that it is parallel to the direction of the field) 

 a force acts on the conductor tending to move it in a direction 

 perpendicular to itself and to the direction of the field. The 

 magnitude of this force depends upon the strength of mag- 

 netic field, the strength of the current in the conductor, 

 the length of the conductor, and the relative direction of 

 the conductor and field. 



Reversibility of Generator and Motor. In the motor, 

 therefore, we must have a magnetic field and conductors 

 so placed in this magnetic field that they may move. The 

 magnetic field of the motor is generally produced by electro- 

 magnets and the conductors are placed on a part of the 

 magnetic circuit, called the armature core, which is free 

 to rotate. Thus the principle parts of the generator and 

 motor are identical and a machine designed for one pur- 

 pose may usually be used for the other. 



In fact, in a power station where several generators 



