EXERCISES 173 



195. Exercises. 



1. Why does the photographer use red light in his dark room? 



2. If you were to hold a suspended pith or cork ball near a sounding 

 tuning fork, what would happen? 



3. Suggest why it is so much harder for a speaker to be heard in the 

 open air than in a hall. 



4. A circular saw has a certain note when revolving rapidly. Why 

 does the pitch of the sound fall when the saw cuts into a board? 



5. Why is the ringing of a bell so much clearer when the sound 

 comes " with " the wind than when it comes " against " the wind? 

 How does the wind affect the shape of the sound waves? 



6. When is a room more likely to have echoes, when full of people, 

 or when empty? Why? 



7. How are the marks upon a graphophone " record " changed into 

 sound? How are the records made? 



8. How can sound waves be carried through a speaking tube? 



9. Of what are " chimes " constructed? How are the different 

 notes secured? 



10. Why can you hear a distant carriage better by putting your 

 ear to the ground? 



11. What is the principle of the yell leader's megaphone? 



