Man's physical universe

xanabras

458 ENERGY MAY BE PROPAGATED BY VIBRATIONS

The Ear Is Remarkably Sensitive.

The human ear can detect sharp sounds that occur at intervals as

close as a twentieth of a second. It can discriminate between tones or

musical notes whose frequency differs by less than 1 per cent. It can

analyze and sort out the components of a mixture of sounds, concentrating

on one at a time. At least a part of this action, of course, must

The other part of it may be due to the fact that we

occur in the brain.

have two ears, which enable us to determine the direction from which

a sound comes. A sound coming from the left will reach the left ear

before it reaches the right ear, and vice versa.

Some deaf persons may be made to hear by vibrations which are

transmitted through the bones of the skull, which cause the liquid

in the inner car to vibrate, provided that the deafness is not due to an

abnormal condition of the inner ear. One can determine whether it is

the inner or outer portions of the ear that are not functioning properly

by use of the tuning fork. If a tuning fork is heard better when it is

placed next to the skull than when placed near the ear, the outer portions

of the ear are abnormal. Certain hearing-devices amplify compressional

waves and change them into vibrations which are transmitted

through the bones near the ear, rather than through the

outer ear.

A very common type of deafness In factories, busy streets, airplanes,

and even classrooms is the deafening due to masking. Under such

noisy conditions one has to

talk as loudly as possible in order to be

heard, and it is no wonder that many students in noisy classrooms do

not hear what the teacher is saying — they are "noise" deaf.

STUDY QUESTIONS

1. Define pitch, intensity, and quality of sounds.

2. How could you prove that sound does not travel in a vacuum?

3. What is the effect of temperature on the velocity of sound in air? Work out

an explanation of this effect.

4. Why does sound not travel through a vacuum?

5. What is the velocity of sound in air?

6. What is a harmonic series of overtones?

7. Suppose that one sees the steam of a whistle one minute before he hears

the sound; how far away is the whistle?

8. What is meant by the frequency of sound waves?

9. Compare sound waves with electromagnetic waves as to the medium in which

they travel and as to their rate of motion and sources.

10. In how many different ways may sounds be produced?

11. What is sound?

12. How may sound waves be analyzed?

13. Why do deaf people often place cupped hands behind their eat-s?

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