6 



beyond the space occupied by the coil, 

 the field within that space may be con- 

 sidered to be uniform. If the axis of 

 rotation passes midway between the sides 

 A and B of the rectangle, the electro- 

 motive forces in both branches of the 

 coil are added, and the total electro- 

 motive force at any moment is according 

 to a well-known formula — 



r 



e = 2 n nz- sin « (1), 



2 



where n is the frequency (number of 

 complete periods per second), r is the 

 number of wires in both branches A and 

 B of the coil collectively, z the total 

 induction through the coil when the Lit- 

 ter stands at right angles to the lines of 

 force, and a the angle between this posi- 

 tion and the position at which the elec- 

 tromotive force e is generated. The re- 

 lation between a and t, the time which 

 was required to rotate the coil through 

 this angle, is a = 2 n n t. The total 

 electromotive force changes periodically 

 from a positive maximum through zero 



