486 Power supplied to the Primary Coil of a Transformer. 



where 



S!=vV + aV- and S 2 = v/r 2 2 + a 2 / 2 2 . 

 Now 



tan^i= — , and taniK = — • 

 rj* TZ r 2 



Hence , , . /, A, 



tan Vi = tan tK, since — = — ? 

 r -' r 3 r 2 



or ^-^ = 0. 



Therefore 



8 = 



£ EjEo 

 2 



^— - COS l|r. 



Now mean power given to the primary coil, or 



EiE 2 



"4" R ' 



For permanent currents, 



Also 



no-!* 



R 



where ^ 

 ft 



is the constant for watts. 





Hence 









Therefore 

 S A S 2 may 



be written 



R rjr 2 





Hence 



r V( i+ ^)( i+ ^) -** 1 + ten2 ♦* 



jy= |. 8.(1 + tap' *,). 



In order that the non-inductive resistance R shall not absorb 

 too much pow r er, B should be the movable coil of the electro- 

 dynamometer, as this is generally the one of lower resistance ; 



5^ should have about the same value as -—^ or 

 Oi fe 2 



B, S 2 . , . 



p" = ^- approximately. 



Vj 1 bj 



