[801.] Power ct ic en ly any Electric Current to any Circuit. 437 



V. 



Approximate Calculation of the Power from the Three Readings of the 



Voltmeter. 



The calculation of the power from formula (1) is easy, especially 

 srhen the voltmeter is graduated to read the mean squares of the 

 '.Ds. and not the square roots of the mean squares. If, however, as 



usually the case, the scale is graduated in square roots, then even 

 ae trouble of taking the squares may be saved, when Vi + V does 

 )t differ much from F, by using the following method : 



Let the inductive resistance be arranged so that FI is nearly equal 



F 2 , and let 



icn, since 



re have by making V 1 equal to F 2 and eliminating F, V it and F 2 

 3m the last two equations, 



1 COS 



Tow the power that would be given to ab (fig. 1) if there were no 

 ag, or the apparent power, as it may be called, would be 



rhereas the power that is actually given to ab is 



FF 2 



COS0. 



lence, 



the apparent power the true power 



-= 1-COS0 



the apparent power 



,, = 2y approximately 



the lag be not very large. 



For example, suppose F t or F 2 were 50 volts, and F were 98 volts, 

 icn T/, or 



VOL. XLIX. 



2 G 



