Учебное пособие Казань-2016 Сайфуллина М. Н., Хабирова Н. М. English for Physicists

59 
Text 2. Properties of waves 
 
 
«Life is a wave, which in no two consecutive 
moments of its existence is composed of the same 
particles» John Tyndall 
 
 
PRE-READING 
Ask and discuss the following questions in pairs/groups 
1.
What makes a wave a wave? 
2.
What characteristics, properties, or behaviors are shared by
the phenomena that we typically characterize as being a wave? 
3.
How can waves be described in a manner that allows us to understand 
their basic nature and qualities? 
Active vocabulary 
 
Word 
Pronunciation 
Translation 
alternate, v. 
/ˈɔːltəneɪt/ 
чередоваться 
amplitude, n. 
/ˈæmplɪtjuːd/ 
амплитуда 
coil, n. 
/kɔɪl/ 
виток; катушка 
crest, n. 
/krest/ 
гребень (волны) 
compression, n. 
/kəmˈpreʃən/ 
сжатие 
dashed line 
/dæʃtlaɪn/ 
пунктирная линия 
density, n. 
/ˈdensɪti/ 
плотность, удельная масса 
displace, v. 
/dɪˈspleɪs/ 
вытеснять, 
заменять, 
syn. 
dislodge 
disturbance, n. 
/dɪˈstɜːbəns/ 
нарушение покоя, волнения 
exhibit, v. 
/ɪɡˈzɪbɪt/ 
выставлять, показывать, syn. 
show, present 
horizontal, adj. 
/ˌhɒrɪˈzɒntəl/ 
горизонтальный 
perpendicular, 
/ˌpɜːpənˈdɪkjʊlər/ 
перпендикулярный 
adj. 
rarefaction, n. 
/reərˈfækʃən/ 
разрежение 
rest position 
/rest pəˈzɪʃən/ 
положение покоя 
rope, n. 
/rəʊp/ 
веревка, канат 
spatial repetition /ˈspeɪʃəl ˌrepɪˈtɪʃən/ 
пространственное повторение 
transverse, adj. 
/trænzˈvɜːs/ 
поперечная 
trough, n. 
/trɒf/ 
подошва (волны) 

60 
wavelength, n. 
/ˈweɪvleŋθ/ 
длина волны 
 
 
READING 
Read and translate the text using a dictionary if necessary: 
A transverse wave is a wave in which the particles of the medium are 
displaced in a direction perpendicular to the direction of energy transport. A 
transverse wave can be created in a rope if the rope is stretched out 
horizontally and the end is vibrated back-and-forth in a vertical direction. If 
a snapshot of such a transverse wave could be taken so as to freeze the
shape of the rope in time, then it would look like the following diagram. 
The dashed line drawn through the center of the diagram represents the 
equilibrium or rest position of the string. This is the position that the string 
would assume if there were no disturbance moving through it. Once a 
disturbance is introduced into the string, the particles of the string begin to 
vibrate upwards and downwards. At any given moment in time, a particle
on the medium could be above or below the rest position. Points A, E and H 
on the diagram represent the crests of this wave. The crest of a wave is the 
point on the medium that exhibits the maximum amount of positive or 
upward displacement from the rest position. Points C and J on the diagram 
represent the troughs of this wave. The trough of a wave is the point on the 
medium that exhibits the maximum amount of negative or downward 
displacement from the rest position. 
The wave shown above can be described by a variety of properties. 
One such property is amplitude. The amplitude of a wave refers to the 
maximum amount of displacement of a particle on the medium from its rest 
position. In a sense, the amplitude is the distance from rest to crest. 
Similarly, the amplitude can be measured from the rest position to the 
trough position. In the diagram above, the amplitude could be measured as 
the distance of a line segment that is perpendicular to the rest position and 
extends vertically upward from the rest position to point A. 

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The wavelength is another property of a wave that is portrayed in the 
diagram above. The wavelength of a wave is simply the length of one 
complete wave cycle. If you were to trace your finger across the wave in the 
diagram above, you would notice that your finger repeats its path. A wave is 
a repeating pattern. It repeats itself in a periodic and regular fashion over 
both time and space. The length of one such spatial repetition (known as a 
wave cycle) is the wavelength. The wavelength can be measured as the 
distance from crest to crest or from trough to trough. In fact, the wavelength 
of a wave can be measured as the distance from a point on a wave to the 
corresponding point on the next cycle of the wave. In the diagram above,
the wavelength is the horizontal distance from A to E, or the horizontal 
distance from B to F, or the horizontal distance from D to G, or the 
horizontal distance from E to H. Any one of these distance measurements 
would suffice in determining the wavelength of this wave. 
A longitudinal wave is a wave in which the particles of the medium are 
displaced in a direction parallel to the direction of energy transport. A 
longitudinal wave can be created in a slinky if the slinky is stretched out 
horizontally and the end coil is vibrated back-and-forth in a horizontal 
direction. If a snapshot of such a longitudinal wave could be taken so as to 
freeze the shape of the slinky in time, then it would look like the following 
diagram. 
Because the coils of the slinky are vibrating longitudinally, there are 
regions where they become pressed together and other regions where they 
are spread apart. A region where the coils are pressed together in a small 
amount of space is known as a compression. A compression is a point on a 
medium through which a longitudinal wave is traveling that has the 
maximum density. A region where the coils are spread apart, thus 
maximizing the distance between coils, is known as a rarefaction. A 
rarefaction is a point on a medium through which a longitudinal wave is 
traveling that has the minimum density. Points A, C and E on the diagram 
above represent compressions and points B, D, and F represent rarefactions. 
While a transverse wave has an alternating pattern of crests and troughs, a 

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longitudinal wave has an alternating pattern of compressions and 
rarefactions. 
As discussed above, the wavelength of a wave is the length of one 
complete cycle of a wave. For a transverse wave, the wavelength is 
determined by measuring from crest to crest. A longitudinal wave does not 
have crest; so how can its wavelength be determined? The wavelength can 
always be determined by measuring the distance between any two 
corresponding points on adjacent waves. In the case of a longitudinal wave, 
a wavelength measurement is made by measuring the distance from a 
compression to the next compression or from a rarefaction to the next 
rarefaction. On the diagram above, the distance from point A to point C or 
from point B to point D would be representative of the wavelength. 
(Adopted from 
www.physicsclassroom.com 
) 
 
 

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