QUESTIONS ON CHAPTER I 



1. Star*- briefly some of the advantages of direct over alternating current 

 for industrial purposes. Whirh type of power supply is best adapted to 

 traction purposes? Why is direct current necessary for electrolytic work? 



2. In spiff of the many advantages of direct current why is a large per- 



power at the present time generated as alternating current? 

 .some secondary reasons for generating power as alternating current. 



3. How does the weight of transmission conductor vary with the .trans- 



it voltage? Give reasons why it may be more economical to generate 

 power in large quantities and transmit it over expensive transmission 

 MS rather than to generate it at the point of use. 



4. What is meant by a sine wave? Do commercial alternators as a rule 

 generate sine waves? Why are sine waves assumed in making alternat ing- 

 current calculations? 



5. Describe a graphical method of producing a sine wave. Show how 

 such a wave may be plotted by the use of sine tables. 



6. Through how many space-degrees must a coil, rotating in a bipolar 

 field, turn Ixjfore one cycle is completed. Under these conditions what is 

 the relation of the space-degree to the electrical degree? What is meant 

 by an alternation? 



7. In a four-pole machine, through how many space-degrees must a 

 coil turn }>efore a cycle is completed? Why? In this case what is the 

 relation between electrical and space-degrees? How fast in r.p.s. must 

 such a coil rotate in order to produce a frequency of 60 cycles per second? 

 In r.p.m? 



8. What are two advantages .f tin- higher frequencies for commercial 

 generation and utilization? Name two distinct disadvantages of the 



higher frequencies 



9. Why i- '>() cycles per second u-ually chosen as the system frequency 

 when a power company supplies both lighting and power loads? Under 

 what conditions is 25 cycles used? What i- the advantage of this frequency 



over QO 



10. What i> the average value of an alternating-current wave over one 

 complete cycle? Cpon what i> the value of an alternat ing-current ampere 

 based Define an alternating-current ampere. 



11. How doc.x the heating eflfe. ' \\ltll the CUITent? 

 How dor> the squared current wave compare with the original current wave 



a regards frequency , maximum value, and its axis of symni< M | What i* 



tlue of a sine wave? What is 

 to average for a ha! atio colled? 



12. Compare 1 ohm resistance for alternating current with 1 oh in resis- 

 tance for du \ is an alternating-current volt defined? 



407 



