32 ELEMENTS OF ELECTRICAL ENGINEERING. 



done by the induced electromotive force in maintaining the in- 

 duced current /. That is : 



Fv = El (ii) 



in which E is the value of the induced electromotive force in 

 abvolts. 



Substituting the value of F from equation (6) in equation (ii) 

 and solving for E, we have : 



That is, the electromotive force E, in c.g.s. units, induced in a 

 straight wire / centimeters long moving sidewise at a velocity of 

 v centimeters per second across a uniform magnetic field of in- 

 tensity eft, is equal to the product IcHv. This result is expressed 

 in abvolts and it is to be divided by io 8 to reduce to volts, that is 



E= 1 ^ volts (19*) 



24. Expression of induced electromotive force in terms of num- 

 ber of lines of force cut per second. During / seconds the sliding- 

 wire AB, Fig. 15, moves over a distance vt and sweeps over Ivt 

 square centimeters of area. Multiplying this area by 3f gives the 

 magnetic flux <( = IvtdC) which passes through the area, and this 

 flux 4> is the number of lines of force cut by AB during the t 

 seconds, so that ^jt( = l3fv = E) is the number of lines of force 

 cut per second by AB. That is, the electromotive force in c.g.s. 

 units induced in a wire is equal to the number of lines of force cut 

 by the wire per second. This proposition is here derived for a 

 straight wire moving sidewise across a uniform magnetic field, 

 but it is true for any wire straight or curved moving in any man- 

 ner in any magnetic field uniform or non-uniform. 



25. Expression of induced electromotive force in terms of the 

 rate of change of the magnetic flux enclosed by or passing through 

 a circuit. As the wire AB, Fig. 15, moves to the right the en- 

 closed area ABCD increases, the magnetic flux through ABCD 



