8 4 



Strike a tuning fork with a soft mallet or rubber ham- 

 mer, and hold it over A so that the flat face of one prong 



is directly above the end of 

 the tube. While the fork is 

 sounding, move B so that the 

 level of the water in A is 

 slowly changed. As the level 

 changes, the loudness of the 

 sound varies, and at one level 

 a very intense sound is heard. 

 At certain other positions of 

 the water in A there is very 

 strong reinforcement of the 

 sound of the tuning fork. 

 Note very carefully one level 

 of the water when decided 

 reinforcement occurs. 



This reinforcement of sound 

 by means of waves reflected 

 from the water is called reso- 



W 



nance. 



FIG. 61. The sound of the tuning 

 fork is strengthened by reflection 

 from the water. 



Repeat the above, with forks 



of different pitch. What conclusion do you draw regard- 

 ing the pitch of a note and the height of a column of 

 air necessary to produce resonance ? 



EXPERIMENT 83. A TEST FOR HEARING 



(a) Sit in a chair and have your laboratory partner hold 

 a ticking watch at the side of one ear. Determine how 

 far the watch can be carried from the ear before it ceases 



