ELEMENTARY LAWS OF CONTINUOUS CURRENTS 21 



detected by Faraday. The laws of induced e.m.f. generally 

 are not expressed in the form given above; they are based 

 on the idea of a complete electric circuit in which the total 

 number of lines of force is either increasing or decreasing. 

 But it seems clearer and easier to consider any wire by 

 itself. Is it generating an e.m.f. or not? Whenever the 

 wire is cutting flux an e.m.f. is generated and the magnitude 

 of this e.m.f. depends entirely upon the rate at which the 

 magnetic flux is cut. When the conductor moves through a 

 magnetic field so as to cut 10 8 lines per second, one volt of 

 e.m.f. is generated in that conductor. 



Magnitude of e.m.f. If the ength of a conductor is 

 I cms. and it is moving at a uniform velocity of v cm. per 

 sec. through a magnetic field of density H lines per sq.cm. 

 and if the motion of the conductor is perpendicular to the 

 direction of the magnetic field and to the length of the 

 conductor, the e.m.f. generated in the conductor will bo 



(-.111. f. (in volts) =lHv/l0 8 (11) 



The necessity for stating the mutual perpendicularity 

 of the motion, field direction, and length of conductor 

 will be easily seen. Suppose that the conductor is moved 

 in a direction parallel to the magnetic field; no flux will 

 be cut by the conductor and so no voltage will be generated 

 in it. Also if the conductor is moved in a direction parallel 

 to its length no flux will be cut and so no e.m.f. will be 

 generated. It sometimes happens in electric generators 

 that the motion of the conductor is perpendicular to its 

 own length but not perpendicular with the direction of the 

 magnetic field. If the motion makes an angle with 

 the magnetic field, the induced e.m.f. is given by the 

 equation : 



e.m.f. (in volts) = IHv sin 6/10 8 . . . (12) 



