508 ALTERNATING CURRENTS 



22. Distinguish between a series arc and a multiple arc. Upon what 

 does the series arc depend for its regulation? What is the object of the 

 series coil? The cut-out switch? Describe the operation of the lamp on 

 starting. 



23. Upon what factor does the regulation of a multiple arc depend? 

 Why are the carbons touching when the lamp is not in operation?- Why 

 are dashpots used in lamp regulating mechanisms? 



24. In what way does the flame arc differ from the ordinary direct-current 

 arc as regards the light source? How may the color of the light be con- 

 trolled? Why are the electrodes consumed very rapidly in this type of 

 lamp? 



26. Give one reason why both electrodes feed from above in the open 

 flame arc. How is the arc flame kept burning in the proper position? 

 Why is this type of lamp used abroad more than in this country? How does 

 the efficiency of this lamp compare with that of other illuminants? 



26. How has the electrode life of the flame arc been increased? How does 

 the efficiency of this type of lamp compare with that of the previous type? 

 Name one good feature of the flame arc. 



27* Of what materials do the positive and negative electrodes in the 

 magnetite arc consist? Why must the copper always be the anode? 



In general how does the regulation of this type of lamp differ from that of 

 other arcs? Why is it different? What is the number of hours that the 

 lamp burns per trim? What is the efficiency of the 4.4-amp. arc? Of the 

 6.6-amp. arc? 



28. What is the principle of the mercury arc? To what is the light due? 

 What is the color effect produced by this type of illuminant ? Is it injurious ? 

 What is its physiological effect? How may the illumination be made more 

 pleasing when these lights are used? What is the efficiency of this type of 

 lamp? 



29. What is the source of light in the Moore tube? What are its advan- 

 tages? Why are these tubes not in more common use? 



30. What is the principle of the Nernst lamp? What can be said of its 

 light and its efficiency? Why is it not in common use? 



31. Why are there excellent opportunities for still further increasing the 

 efficiencies of illuminants? 



32. What is photometry? In what way are the measurements generally 

 made? Name a very marked source of error in photometric measurements. 



33. Upon what principle is the Bunsen photometer screen based? How 

 is the position of balance determined? How is the candlepower calculated 

 after a balance has been obtained ? 



34. Why is a candle itself seldom used at the present time as a working 

 photometric standard? What are used as standards? Sketch the con- 

 nections which facilitate voltage adjustment when a photometric measure- 

 ment is being made. 



36. How is the position of balance determined when a Lummer-Brodhun 

 photometer screen is used? How may errors due to differences in the white 

 screens be eliminated? 



