94 



CURRENT VALUE. 



50 



y! 



The equivalent direct voltage is thus in the present case 

 = 35-35, and the alternating voltage would be spoken of 



as a virtual voltage of 35-35 volts. 



Suppose, now, that the voltage applied to the voltmeter 

 wire is doubled, the current which it will send through the 

 wire will be doubled, and the value of C'*R throughout each 

 cycle will be four times as great as before. Thus heat will 

 be developed four times as rapidly and the expansion of the 

 wire will be four times as great. Consequently, the deflection 



100 



corresponding to -^ or 70 7 volts will be four times as great 

 V * 

 50 

 as for the original r^ or 35-35 virtual volts. The nature of the 



V 



scale of a Cardew voltmeter is shown in Fig. 42, where the inner 



FIG. 42 SCALES OF VOLTS AND (VOLTS)*. 



scale represents the scale of volts, and the outer evenly 

 divided scale shows the graduation, which would be 

 obtained by plotting the squares of the voltages, which are 

 proportional to the expansion of the wire producing the 

 deflections. It is thus seen on the figure that the deflection 

 corresponding to 70 volts is four times the deflection for 35 

 volts, and that a practically uniform scale would be obtained 

 if the graduations were measured in (volts) 2 instead of volts. 



