CHAP. IV] 



INDUCED E.M.F. 



57 



argument in favor of the theory of " cutting " of lines of force. 

 He showed that no e.m.f. is induced in an electric circuit when a 

 flux is brought in or out of it without actually cutting any of the 

 conductors of the electric circuit. For practical purposes it is 

 convenient to distinguish the transformer action from the genera- 

 tor action, so that the matter of unifying the statements (1) and 

 (2) into one more general law is of no immediate importance. 



24. The Formulae for Induced E.M.F. In accordance with the 

 definition of the weber given in Art. 3, we have 



e=-dti/dt, (25) 



where e is the instantaneous e.m.f. in volts, induced by the trans- 



FIG. 11. E.M.F. induced by transformer action. 



former action in a turn of wire which at the time t is linked with a 

 flu\ < .1 (J> we I x>rs. The value of e is determined not by the value of 

 <I> l>ut by the rate at which Ovaries with the time. In the case of tin- 

 generator action d(J> in formula presents the llux which the 

 conductor un<l< T < onsideration cuts during the interval of time dt. 

 It can be shown that the two interpretations of d4 lead to the 

 same result. Namely, in the case of the transformer act inn d'i-. 1 1 . 

 the new flux, </#, is brought within the secondary turn by cutting 

 tli rough the conductor of this turn. Therefore, in the case of thr 



mental Law of Eloctromnini. tir Induction, Trans. Amur. In*. Ebc. Eng%. t 

 7 (1908), Part. 2, p. mi. I lc, Das InduktiooHpnU, idb- 



/um lu.lukti 



! >. Baillrharlir. Sur l:i l..i dr rindurti.m, BuU. SocuU 

 national* d* EbctricitM, Vol. I" l ' 10), pp. 89 and 288. 



