rit i! -F:M Mmi,,\ 37 



together. It" tin- loml i^ nothing tin- rum-lit i- nothing', 

 if thf load resists tin* motion the current Hows from the 

 liii". if the load assist* tin- motion the current Hows into 

 tin- linf . 



We ran thus change the sign of the current by reversing 

 tli.- load, so that a dynamo will act as a generator or 

 as a motor according to the sign of the load, and thf 



change from thf <>M,> to t! th.-r is through the value of 



zero load. 



During the process of a reversal of the load the sign <>f 

 luced tension is unaltered, hence a dynamo does not 

 reverse its direction of rotation when changing from 

 generator to motor. This is seen also from K<|iiati<>M I-;. 

 which shows that whatever be the sign of r, n can only be 

 negative when c is negative, and -!! greater thai 



The direction of rotation may of coarse be reversed by 

 changing either the sign of the terminal tension or the 

 sign of the magnetic field. If both are changed simul- 

 taneously, the direction of rotation is unchanged. Th- 

 usual method of reversing is to bring the m-t-.r to real, 

 reverse the sign of the terminal tension, ami then -tart 

 up in the c ml i nary way. 



change in the sign of the current consequent upon 

 a change in tin- sign of the load in clearly shown in the 

 figure. For anycurn-nt. "//'. ilflivfnnl into the line, tin- 

 energy per seoond expended in hf.it is represented by th<- 

 area OW'A"//' ; the energy given to th- linf. ln'ini th 

 prrxluct of the curn-nt atnl th -i of th- lin.-. is 



represented by the area O/>A*'//'; the whole eiiftyy c\- 

 pmle<l i* thus represented by the area Df\ '/ "'.'. and this 

 is equal t> th> input of energy in the form of work done, 

 ve see to be true, since K'F' represents the speed 



