114 



TREATISE ON ALTERNATING CURRENTS. 



per cent, of the whole volume, V should be correspondingly 

 increased to about 51493 cubic centimetres. 

 Now 



AN, I . db 



EI = 7=- x maximum value of - 

 \/2 10 8 dt 



therefore 



10S/2 



10*% 



10 8 x 1000 



X TT x 50 X 2500 

 180000, nearly . . . 



(15) 



Suppose, now, that the primary circuit is wound with 230 turns 

 and the secondary circuit with approximately 23 turns. The 

 primary coil will be wound with the equivalent of No. 10 S.W.G. 

 wire, and will have an area, when double cotton-covered, of about 

 0*0177 square inch. The secondary wire will be equivalent to 

 No. 3/ S.W.G., and will, including insulation, have an area of 

 about 0'126 square inch. 



The primary coil will, therefore, require a winding space of 

 about 5 '175 square inches, and the secondary coil a winding space 

 of about 3*68 square inch. 



Thus the total winding space required for the two coils is 



9 square inches, or, allow- 

 ing 25 per cent, for insu- 

 lation between the two coils 

 and between different layers 

 of the primary, we may 

 take the winding space re- 

 quired to be 11*25 square 

 inches, or 73 square centi- 

 metres. 



FlG 39 Suppose, now, that we 



select a transformer of the 



Mordey type (see Fig. 39) in which the width, DC, bears to the 

 depth, CB, the ratio of 3 : 2. The length, DE y may be altered 

 to suit the circumstances of the case. 



