90 



ELECTRICAL ENGINEERING 



When the current is i = I = 10 c.g.s. units, the energy stored is 



/2 1Q2 



W = X ^ = 10 6 X ^- = 5 X 10 7 ergs 



= 5 X 10 7 X 10~ 7 = 5 watt-seconds. 



67. Mutual Inductance and Self-inductance. The mutual 

 inductance of one circuit upon a second circuit is the number 

 of interlinkages of the second circuit with the flux produced by 

 unit current in the first circuit. It is equal to the mutual in- 

 ductance of the second circuit upon the first and is represented 

 by 9ft. 



A and B, in Fig. 69, are two electric circuits of n\ and n^ turns 

 respectively interlinked with one magnetic circuit of reluctance eft. 



FIG. 69. Mutual inductance. 

 The flux produced by unit current in A is 



and the inductance of A is 



= -~- c.g.s. units; 



if all the flux produced by A passes through B, then, the mutual 

 inductance of A upon B is by definition 



c.g.s. units ..... (126) 



