ELECTRICAL MACHINERY 469 



A ohms A ohms 4ohms passes through the resist- 



rnnrmTjrmTOnnrnT^ 1 ance B, which can be in- 

 I creased or decreased as the 



FIG . 350 SERIES CONNECTIONS metallic arm C is moved 



from point to point, and out 



through the arm C and pivot D. The rheostat absorbs 

 energy and throws it off as heat instead of doing useful 

 work with it. 



621. Series connections. When lines are connected up 

 as in Fig. 350, so that the same current flows through 

 each one of them in succession, they are said to be con- 

 nected in series. In this case the total resistance is the 

 sum of the several resistances. 



4 + 4+4 = 12. 



622. Parallel connection. If instead of connecting 

 these lines up as in Fig. 350 they be connected as 

 in Fig. 351 they will be in parallel and the total resistance 

 will be only one-third of the resistance of one of them. 

 This is obvious, for in this connection there is three times 

 as much cross-section of wire carrying the current as in 

 the previous case, and by formula (A) the resistance 

 varies inversely with the sectional area. 



623. Shunts. One line connected in parallel with an- 

 other is said to be a shunt connection to the other. In 

 Fig. 35IA, S is shunted across the resistance R. If R has a 

 greater resistance than 5 it will carry less of the current, 

 since the currents carried are inversely proportional to 

 the resistance. Hence if R has a resistance of 5 ohms 

 and vS a resistance of I ohm, R will carry one-fikh as 

 much current as S or one-sixth of the total current. 



FIG. 351 PARALLEL CONNECTIONS FIG> 35 IA SHUNT 



