Sound waves

We have learned that heat is due to the vibration of the molecules of a substance. The more violently the molecules of an object vibrate, the greater is the intensity of heat possessed by that object. Sound waves, however, are produced by the vibratory motion of the object as a whole, such as the prong of a tuning fork, a stretched vocal chord, or a tightened string. Sound waves reach our ears and stimulate the auditory nerves so that we have the sensation of sound. How many sound waves must reach our ears per second for us to be aware of a sound? Individuals vary greatly in the ability to hear a sound. Between 16 and 16000 vibrations per second has often been given as an answer to the above question. Some persons cannot hear as few as 16, others can not hear as many as 16000. many individuals can hear sounds that have a frequency as 19 or 20 thousand vibrations per second. Accordingly, the frequency range of 16 to 20 000 vibrations per second is considered the audio-frequency range.

The sounds vary in loudness, pitch, and quality. The sound waves may be reflected to produce echoes. They may also be amplified or absorbed as we please. Some sounds are harsh and discordant, and their intensity measured in decibels may be almost painful. Other sounds are pleasing, and seem to act as a sedative for ever wrought nerves and weary muscles. Above the range of frequencies which the normal human ear can hear is a wide range of inaudible sound vibrations called ultrasonic waves. Their frequency may vary from 15000 to as high as 500 000 000 vibrations per second.

Ex. 1. Give the main idea of the text.

Velocity of Sound

The velocity of sound depends on the density and the elasticity of the medium. The greater the elasticity and the less the density, the greater is the velocity.

Intensity of sound

When sound waves spread out in every direction from a source of sound, the intensity varies inversely as the square of the distance from the source. In this case, the sound waves spread out as spheres. The same amount of energy is transmitted across every spherical surface having its centre at the source of sound. The larger the surface of these spheres, the smaller the energy that goes through each square centimetre of surface. The surfaces of these spheres increase as the squares of their radii increase. Hence, the energy that passes through unit area decreases as the squares of the radii increase.

Ex. 2. Translate into Russian paying attention to participles

1. Copper is of great value, being a good conductor of electricity. 2. Having a high melting point tungsten is widely used for the production of electric lamps. 3. Raising the temperature, we speed up the rate of reaction. 4. When completed this reaction will give us a new artificial substance. 5. Having been supplied with all necessary equipment the scientist performed the experiment successfully. 6. The research being made in this laboratory is of great scientific importance. 7. From the

electric viewpoint a negatively charged body is one having more than its normal number of electrons and a positively charged body is one having less than its normal number of electrons. 8. Having lost some of its electrons, the atom has a positive charge; having an excess of electrons - it has a negative charge. 9. When placed in a magnetic field, the molecules of steel do not readily turn around in the direction of the lines of force.

Ex. 3. Re-state the following sentences using the Present Participle instead of the subordinate clause. Follow the model.

Sp.: As he realized the difficulties involved in that problem he gave up the idea of solving it.

St.: Realizing the difficulties involved in that problem he gave up the idea of solving it.