QUESTIONS AND PROBLEMS 507 



the greatest intensity? Of the least intensity? Of what commercial use 

 MIT these distribution cur 



10. What is meant by incandescence? How does the light emitted by 

 an incandescent substance vary with its temperature? Does this bear 

 any relation to the efficiencies of various illumin.-r 



11. Iti what way does luminescence differ from incandescence? 

 .pies of luminescent sources of light. 



12. Name two essential requirements for an incandescent lamp filament. 

 Why was a carbon filament practically the only satisfactory filament for a 

 number of years? How does a "G. E. M." lamp filament differ from the 

 ordinary carUm filament? What are its advantages? What are tin 

 efficiencies of these two filaments? 



13. What are the objections to a carbon filament? Is it possible to in- 

 crease the efficiency of a carbon filament lamp/ What must be sacrificed 

 in order to do this? What is the approximate life of a carbon filament 

 lamp? When does it become more economical to throw away a lamp 

 rather than continue its use? 



14. Why does a tantalum lamp develop a higher efficiency than a c 

 lamp? About what efficiency docs the tantalum lamp develop 



the average life of such a lamp? What is its peculiarity when used with 

 alternating current ? 



15. Why is tungsten particularly well-adapted to being used for lamp 

 nts? What is the difference between a drawn and a pressed filament? 



Compare the two. What are the approximate efficiencies of "Mazda" 

 lamps? What is the guaranteed life of such a lamp? \\h\ docs the 

 tungsten lamp take an excessive current when it is fir- 1 I on? 



16. What factor limits the operating temperature of the vacuum tur 

 lamp? What two effects are produced? How may one of these factors 

 be minimi. 



17. What is t ; principle of the pas-filled lamp? Why is an inert 

 gas necessary? Why does this type of lamp have a long narrow neck 1 .' 



iocs the filament differ in shape from that of the vacuum lamp? 



Why are the efficiencies higher in the larger units'.' How may daylight U- 

 approximated with these lamps? 



18. What is the basic principle of the arc light? Why is the arc . 



'luminant ? V he reason that tin :nt !M> 



fed directly across the line? \\hat is the "ballast" and approxi- 



ige of thi- power is lost in the ballast? 



19. What is the principal source of light in tin- ' arc? 



mines tli positions of the two electrodes? Which is 



consumed the fast. 



20. Compare the arc with the dircct-n 

 Why is a n-nVrtor - Me in tl.- 



advantage has the alternating-current multip 

 mult ; 



21. V .-nclosinr ts efficiency and U|HMI the 



s of the enclosed arc over the 

 Where are open direct-^ nmonly used? 



