UNIT 18

 

I. Find out the words in the dictionary. Write them down and learn.

 

alternate, to alter, compression, rarefaction, originate, vocal cords, throat, drum, string, to convert, longitudinal, transverse, propagation, large-coiled, backward and forward, to bunch, to occur, to distinguish, pure, pitch, intensity, to assess, to perceive, to diminish, to affect

 

II. Read the text. Use a dictionary, if necessary.

 

Text: “Sound”.

 

Sound consists of waves of alternate compression and rarefaction that transmit kinetic energy through a medium. If there is no medium, there is no sound; sound waves cannot pass through a vacuum. All sounds originate from vibrating objects, such as the vocal cords in the human throat, the skin of a drum, or the strings of a violin. The vibrations are then passed on through a medium – most commonly air – until they strike the ear drum; the ear converts the vibrations into nerve impulses, which pass to the brain where they are interpreted as sounds. Microphones are the other most common instruments of sound waves into electrical signals.

Waves and sound.There are two types of waves in physics: longitudinal and transverse. Sound waves are of the longitudinal type – that is, their vibrations take place in the same direction as they travel. The phenomenon of longitudinal wave propagation can be demonstrated with a long, large-coiled spring. When the string is fixed at one end and the other end is moved backwards and forwards, alternating regions of compression (where the coils are bunched together) and rarefaction (where the coils are farther apart than normal) move along the spring.

Transverse waves are those in which the vibrations occur at right angles to the direction, in which the waves travel – as happens, for example, when a length of rope is moved regularly up and down to give it a wavelike appearance. Ocean waves and light waves also travel by transverse propagation.

Frequency and intensity. Two obvious ways of distinguishing one “pure” sound (that is, a “pure” tone) from another are by their pitch and loudness. Neither property is a scientifically accurate notion. Pitch is a word used by musicians and is closely related to frequency; but it is a subjective term, whereas frequency can be measured physically. Similarly loudness, closely related to a sound’s intensity, differs according to the sensitivity of the hearer’s ears, whereas intensity can be measured in exact physical quantities. (Real sounds are mixtures of many different pure sounds and also have a characteristic “quality”, which can be assessed by detailed examination of the shape of a real sound’s waveform.)

The frequency of a sound wave is the number of wavelengths that are completed in a given period of time. The universal unit of measurement is the hertz (Hz), which represents one complete wavelength, or cycle, per second. The human ear is sensitive to sound in the frequency range from about 20 Hz. As people grow older, their ability to perceive high frequencies diminishes.

The intensity of sound is measured in terms of the amount of power that passes each second through a given area perpendicular to the direction of the sound wave. The intensity unit is the decibel (db). There is no absolute decibel scale; it is a relative scale.

Velocity. Sound can be transmitted by any medium – gas, liquid, or solid – and all sound waves travel at a constant velocity through any given medium at a constant temperature. But depending on their elasticity and density, some mediums transmit waves faster than others. It is extremely difficult for sound waves to pass from a medium of one density to another of a much higher or lower density.

Anything that changes the density of a medium also alters the speed at which sound travels through it. Hence the velocity of sound is affected by temperature; as the temperature increases, the medium expands. Its density decreases, with the result that the velocity of sound increases.            

  

III. Find the sentences that can’t be found in the text.

 

1. A sound wave consists of a series of alternate compressions and rarefactions of the medium through which it passes.
2. Waves of alternate compression and rarefaction transmit kinetic energy through a medium.
3. The vibrations pass through a medium and it works by converting sound waves into electrical signals.
4. The power of sound, perceived as loudness, is measured in decibels.
5. The decibels scale is a relative one, with an arbitrary zero point (usually taken as the lower threshold of human hearing).
6. There are two types of waves in physics: longitudinal and transverse.
7. As with longitudinal waves along a spring, sound waves consist of a series of compressions and rare factions.
8. The wavelength is the distance between two adjacent points (or particles) that are in the identical phase of the wave’s vibration.

 

IV. Translatethe following noun groups into Russian.

 

1. the skin of drum _____________________________________________
2. the strings of violin ___________________________________________
3. common instruments of sound detection __________________________
4. phenomenon of longitudinal wave propagation _____________________
5. regions of compression ________________________________________
6. sensitivity of the hearer’s ears ___________________________________
7. mixtures of pure sounds ________________________________________
8. detailed examination of the shape ________________________________
9. the shape of a real sound’s waveform _____________________________
10. frequency of a sound wave ______________________________________
11. number of wavelengths _________________________________________
12. intensity of sound _____________________________________________
13. a medium of one density _______________________________________
14. velocity of sound _____________________________________________

 

V. Find English words and equivalents in the text.

 

1. чередующиеся сжатия ____________________________________
2. передавать кинетическую энергию _________________________
3. происходить ____________________________________________
4. преобразовывать в импульсы ______________________________
5. в том же направлении _____________________________________
6. может быть показана ______________________________________
7. зафиксированная нить _____________________________________
8. подобно _________________________________________________
9. данный период времени ___________________________________
10. возможность воспринимать ________________________________
11. направление звуковой волны _______________________________
12. быстрее, чем другие _______________________________________
13. более высокой или более низкой плотности ___________________

 

VI. FindRussian equivalents to the following words and expressions in the text.

 

1. alternate compression ____________________________________
2. originate from vibrating objects _____________________________
3. sound detection __________________________________________
4. to be father apart _________________________________________
5. to move backward and forward ______________________________
6. right angle ______________________________________________
7. to move up and down _____________________________________
8. a scientifically accurate notation ____________________________
9. to be completed in a given period of time ______________________
10. intensity unit _____________________________________________
11. as the temperature increases _________________________________
12. the medium expands _______________________________________

 

VII. Fill in the missing words.

 

1. Sound consists of waves of _____ compression and _____.
2. If there is no _____, there is no sound.
3. Sound waves are of the _____ type – that is their vibrations take place in the same direction as they _____.
4. When the spring is fixed at one end and the other end is moved _____ and _____.
5. _____ waves are those in which the vibrations occur at _____ _____ to the direction
6. Ocean waves and light waves also travel by transverse _____.
7. The obvious ways of distinguishing sound are by their _____ and _____.
8. Real sounds are _____ of many different pure sounds.
9. The universal unit is the _____.
10. The velocity of sound is _____ by temperature.

 

VIII. Fill in the preposition, if necessary.

 

1. Sound waves cannot pass ___ a vacuum.
2. All sounds originate ___ vibrating objects.
3. The vibrating objects are then passed ___ ___ a medium.
4. The phenomenon of longitudinal wave propagation can be demonstrated ___ a long, large-coiled spring.
5. Pitch is a word used ___ musicians, and it is closely related ___ frequency.
6. Frequency can be measured ___ physically.
7. The human ear is sensitive ___ sound  ___ the frequency range ___ ___ Hz.
8. The intensity of sound is measured ___ terms of the amount of power.

  

IX. Define whether sentences are true or false.

      

1. All sounds originate from still and vibrating objects, because all objects have their own waves.
2. Microphones can’t be instruments of sound direction, because we used them just to close our ears.
3. When the spring is fixed at one end and the other end is moved backward and forward, alternating regions of compression move along the spring.
4. Loudness, closely related to a sound’s density, and depends on the sensivity of the hearer’s ears.
5. The frequency of a sound wave is the number of vibrations that are completed in a given period of time.
6. The human ear is sensitive to sound in the frequency range from about 10 Hz.
7. As people grow older, they loose their ability to perceive high frequencies.
8. The intensity of sound is the amount of power that passes each second through a given area perpendicular to the direction of the sound wave.
9. There is absolute decibel scale.
10. Sound waves depend on velocity and temperature of a medium.

 

X. Practice with someone asking and answering.

 

1. What originates from vibrating objects?
2. How can all living beings hear sounds?
3. What are the types of waves in physics?
4. What kind of experiment can show us the phenomenon of longitudinal wave propagation?
5. Are there any ways of distinguishing one “pure” sound from another object? What are these ways, if any?
6. What is intensity of sound?
7. How does sound depend on medium and temperature?

 

XI. Put questions to the following sentences.

 

1. Sound waves cannot pass through a vacuum. (Disjunctive)
2. The ear converts the vibrations into nerve impulses. (Special)
3. Microphones are the most common instruments of sound detection. (What)
4. Frequency can be measured physically (General)
5. Decibel scale is a relative scale. (Alternative)

 

XII. Dictate the following text in English to your fellow-students.

 

1. A sound wave consists of a series of alternate compressions and rarefactions of medium.
2. Alternate compression and rarefaction transmit kinetic energy through a medium which they pass.
3. Sound can not pass through a vacuum.
4. Vocal cords in human throat, the skin of a drum or the strings of a violin are good examples of vibrating objects.
5. The phenomenon of longitudinal wave propagation can be demonstrated with a long large spring.
6. Each complete wave cycle is made up of one compression and one rarefaction.
7. The wavelength is the distance between two adjacent point, that are in the identical phase of the wave’s vibration.

 

XIII. Dictation- translation.

 

1. Звук состоит из чередующихся сжатий.
2. Звука нет, если нет среды.
3. Все звуки происходят от колеблющихся предметов.
4. В физике существуют 2 типа волн: вертикальные и горизонтальные.
5. Вертикальные линии могут быть продемонстрированы при помощи длинного шнура.
6. Горизонтальные волны – это волны, в которых вибрация происходит под прямым углом  по отношению к направлению движения.
7. Частота звуковой волны - это количество длин волны, которое заканчивается в данный период времени.
8. Универсальная единица измерения частоты волны звука – это Герц.
9. Интенсивность звука измеряется в форме количества силы, которая проходит каждую секунду через данную площадь, перпендикулярную направлению звуковой волны.
10. Универсальная единица измерения интенсивности звука – это Децибел.