CHAPTER III. 



The Production of Alternating Electromotive Forces Generators Armature 

 I Reaction Circuit with Constant Inductance Impedance. 



THE PRODUCTION OF ALTERNATING ELECTROMOTIVE FORCES. 



GENERATORS. 



16. When a closed circuit moves in a magnetic field the rate 

 of cutting lines of magnetic force is the same as the rate of 

 change of the magnetic flux through the circuit, for since the lines 

 of force themselves always form closed curves the flux through 

 the circuit cannot change without a corresponding cutting of 

 magnetic lines. 



Suppose that a single plane closed circuit 

 rotates with uniform angular velocity about 

 an axis in its own plane at right angles to 

 the direction of a uniform magnetic field. 



Let be a point of the axis OX of 

 rotation of the coil, OF the direction of 

 the field at right angles to OX, and ON 

 the normal to the plane of the coil at time 

 t, and let the angle, measured in a counter- 

 clockwise direction, between OF and ON be 0. 



If B is the intensity of the field, and A the area of the coil, 

 the total flux N through the circuit at the time t is given by 



N = AB cos 9 



since A cos is the projection of A at right angles to B, or B cos 

 is the component of the intensity normal to the plane of A. 



If the angular velocity of the coil is p, and t is measured from 

 the instant when ON and OF coincide, then 



FIG. 2. 



= 



