ELECTRIC CIRCUITS 



85 



but 



therefore, 



+ h + 1 3 



i+i 



Ri Rz 

 E 



E{ ^+TT+^ 



,/L! lz -fts 



1 



(119) 



Rl RZ RS 



If the conductances G, GI, G 2 and G s are used instead of the 

 terms -5, 5-, D~ an d H- the result can be written 



fl til tiz ^3 



or 



= 

 G 



G = Gi + ft + G, 



3, 



(120) 



that is, the conductance of a circuit consisting of a number of 

 parallel branches is equal to the sum of the conductances of the 

 branches. 



63. The Potentiometer. The potentiometer shown in Fig. 

 68 gives a means of obtaining a variable voltage EI from a 

 constant supply voltage E in a continuous current circuit. 



I } 



R 3 



FIG. 68. Potentiometer. 



Determine the voltage EI across the circuit AB and the cur- 

 rent Ii in the circuit in terms of the applied EI and the resist- 

 ances, #1, #2 and RZ as indicated in the figure. 



Now 



I = Ii + It, 



