ELEMENTS OF ELECTRICAL ENGINEERING. 



the arc, and a wattmeter indicates 440 watts delivered to the arc. 

 What is the power factor of the arc ? Ans. 0.865. 



19. A coil of wire which is connected across I lo-volt alter- 

 nating current mains, takes 10 amperes of current. The resist- 

 ance of the coil is 2 ohms. What is the power factor of the coil ? 

 Ans. 0.182. 



20. A wattmeter is connected as shown in Fig. 2O/. The re- 

 sistance of the coil B is 5 ohms. The wattmeter indicates 55 

 watts when used to measure the power delivered to a single lamp 

 which takes one ampere of current. What is the true power de- 

 livered to the lamp ? Ans. 50 watts. 



Fig. 20A 



Fig.21>. 



21. A wattmeter is connected as shown in Fig. 21 p. The re- 

 sistance of the circuit AR is 1 , 200 ohms. The wattmeter indi- 

 cates 60 watts when used to measure the power delivered to a 

 no-volt glow lamp. What is the true power delivered to the 

 lamp ? Ans. 49.92 watts. 



CHAPTER III. HARMONIC ELECTROMOTIVE FORCE AND CURRENT. 



22. Two alternators A and B are connected in series. The 

 electromotive force of A is 1,100 volts, and the electromotive 

 force of B is 1,200 volts. The electromotive force of A is 90 

 ahead of the electromotive force of B in phase, (a) What is 

 their combined electromotive force ? The two alternators give a 

 current of 125 amperes which lags 30 behind their resultant 

 electromotive force in phase, (b) What is the power output of 



