QUESTIONS AND I'!;<>KLl-:.\fs 471 



etc., more common than series grouping. How may the resultant of several 

 currents be found? In what way does parallel resonance differ from series 

 resonance especially with regard to the value of the current? In what 

 way are the two similar? 



17. Explain why the alternating-current resistance of an iron-cored 

 impedance coil differs from the direct-current resistance. How may thin 

 resistance be taken into consideration when the impedance coil is connected 

 in circuit with resistance, etc? 



18. How may the 'phase relations existing in a series circuit having two 

 component voltages be determined when the voltages across the various 

 parts of the circuit are known? Make a sketch. How may the power and 

 the power-factor of all parts of the circuit be determined ? 



19. Explain why a circuit in which the line voltage and three component 

 voltages are all known in magnitude only, cannot be determined unless one 

 more factor be known. What additional information makes the circuit 

 relations determinate. 



20. In what way is the polygon of currents similar to the polygon of 

 voltages? In what way do the two polygons differ? 



21. What is meant by energy current? What relation does it i>ear to the 

 power? What is quadrature current and what relation does it bear to 

 the power? Why is quadrature current usually undesirable? 



PROBLEMS ON CHAPTER II 



18. A certain lamp load consists of 50 60-watt lamps, each lamp having 

 a resistance of 220 ohms. Compare the power taken by this load when 

 connected across 113 volts direct current and across 113 volts alternating 

 current. 



19. A certain transformer takes 30 kw. at 2,200 volts and the current is 

 \") amp. What is the power-factor of this load? 



20. A single-phase motor takes 4.68 kv-a. (kilovolt-amperes) at 220 

 volte and at a power-factor of 0.80. How much power and how much 

 current does it take from the line? 



21. A non-inductive resistance of 12 ohms is connected across 120-volt 

 alternating-current mains. What current and what power do-> it t 



22. Determine the current taken by a coil having o :> henry inductance, 

 when connected across 1 15-volt 60-cycle main- ; I !.">-%.. It 25-CyclC mains. 



23. A coil whose resistance is negligible but which h:us an inductance of 

 0.2 henry i> connected BXSTOM IlM-voli 25-Cycfc mains. <,; \\hat current 

 flows? (/; For what value of frequency will the current be J ft] 



24. A ...nden er whose capacitance is 12 m.f. is connected across 220- 

 > .vie mains, (a) What current does it take? What would be the 



current it" the frequency were 133 cycles per second? 



26. It is desired to obtain 16 um p. leading current by t he use of a condenser 

 connected across 220-volt 60-cycle mains. 



(a) I re necessary? (6) What is the kv-a. cap:.. 



this condenser? (c) What would the kv-a. capacity of the condenser, 



