POWER AND POWER-FACTOR 



59 



In order to illustrate this, the same curves are redrawn in 

 Fig. 26 with the volts and amperes coincident in phase, 

 together with the curve showing the power which would be 

 in the circuit in this case. The dotted line CD gives the 

 average height of this curve, and shows what would be the 

 average power given to the circuit if this had been non- 

 inductive. The value of this average power is 500 watts. 



From this it is evident that with given values of current 

 and voltage the power developed will not be simply the 



Fi. 26. CURVKS OF CUKBENT, VOLTAGE, AXD WATTS. Current and voltage in phase. 



product of these quantities, but will depend upon the difference 

 in phase between them. When the current and voltage are 

 in phase there is no negative power, and the power developed 

 in the circuit has its greatest value. 



This value is the product of the current and voltage as 

 read upon an ammeter and voltmeter. * The product of current 

 and voltage is often called the apparent watts of the circuit, 

 or sometimes the volt-amperes. 



* The relation between the reading of an ammeter or voltmeter and the 

 maximum value of the variable current and voltage is given in the next 

 chapter. 



