SOUND
Class X - Physics
Module Objectives
• Understand Sound – frequency and behaviour.
• Ultrasonic sound and infrasonic sound.
• Applications of ultrasonic sound.
• SONAR in detail.
• Ultrasound scanner in detail.
• Doppler Effect.
Introduction
• Sound
 form of energy
 produced by vibration of bodies
 propagated in the form of waves.
 What is a wave?
 A wave is a periodic disturbance propagating through a medium,
carrying energy. A wave is described in terms of its frequency (f)
wavelength (Λ) and velocity (v).
 These are related by the equation 𝑣 = 𝑓Λ
 Through material medium
Sound
• When a drum is struck
• The drumhead vibrates
• The vibrations are transmitted through the air in the form of
waves.
• When they strike the ear, these waves produce the sensation
of sound.
Interesting Facts about Sound
 Light travels faster than sound.
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eg. the lightning before you hear the thunder.
eg.- When you hear an airplane, look up! If the plane is up high, and you
look at it, the sound will seem to be coming from BEHIND the plane, instead of
straight from the plane. That's because the light that is reflecting off the plane
into your eyes is much faster than the sound that the plane's jet engines are
making.
 Sound travels through air at about 770 miles per hour.
 The speed of sound changes depending on the temperature - warmer days
make sound travel faster
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colder days make it travel slower
 WHY???This is because the air is less dense on warm days, so there aren't as
many air molecules to move to get the sound from point A to point B
 Echo – reflection of Sound
Types Of Sound
• Vibrations of any body can produce a wide range of
frequencies.
• Audible range = 20Hz to 20,000 Hz(for humans)
• Infrasound - below the range of human hearing
• Ultrasound - above the range of human hearing(another
name of ultrasonic sound).
• Animals such as cats, dogs and bats can hear sounds of other
frequencies.
Topic
Properties of Infrasonic and Ultrasonic sound
Ultra sonic Sound
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Frequency Range = 20kHz to 5 x 105 kHz.
Range of wavelengths is from 1.65 cm to about 6 x 10-5 cm.
Branch of science that deals with ultrasound is called ultrasonics
Propagation – similar to sound wave
Speed - same as sound wave
Energy – higher than normal sound due to high frequency.
Infrasonics Sound
• Sounds of frequency below 20Hz
Uses Of Sound
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NDE = NONDESTRUCTIVE EVALUATION
Uses of Ultrasonic waves
• Study of ultrasonic waves in a medium gives information
about its physical properties like elasticity, configuration of
atoms etc.
• Detect cracks and flaws in metal moldings.
• Manufacture alloys, for mixing of immiscible(incapable of
mixing) liquids and to manufacture emulsion for photographic
films.
• Welding, local heating and drilling small holes in hard
materials.
Uses of ultra sonic waves
• Serve as insect repellants. Strong beam of ultrasonic waves
kills bacteria. They are used for sterilisation purposes.
• Cure neuralgic and rheumatic pains.
• Surgical instruments vibrating at ultrasonic frequencies are
used in bloodless surgery.
• Break gallstones and stones in the kidney.
SONAR – most popular application of ultrasonic wave
• SONAR - SOund, Navigation and Ranging
• Invented by Paul Langevin a French Physcist.
• Invention was inspired by ‘Titanic’ disaster.
• Was developed as a means of tracking enemy submarines
during World War II.
• Measure the distance, direction and speed of underwater
objects.
Working Of SONAR
• Sonar consists of a transmitter and receiver.
• Transmitter- produces and transmits ultra sonic waves.
• Ultrasonic waves travel through water until they strike an object.
• The waves on striking object get reflected.
• The reflected waves return to SONAR- detected bythe receiver in
SONAR.
• Detector converts the ultrasonic waves to electrical signals which
are appropriately interpreted.
Topic
Distance calculation using SONAR
• The time interval between transmission and reception is
recorded.
• The distance of the object is calculated.
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t - the time elapsed between transmission and reception of
the ultrasound signals.
• V - the velocity of sound through water .
• distance d of the object is given by d = Vt/2.
• This is called echo-ranging.
Example
• The ultrasound signal sent by Sonar takes 3s to return.
• The velocity of sound in water = 1.5 km/s.
• The distance travelled by the signal =
= Velocity (v) X time (t)/2.
Velocity X time = (1.5 x 3) = 4.5 km.
The distance of the object is (4.5/2) = 2.25 km.
Uses of SONAR
• used to locate submarines and icebergs.
• used to determine depth of a sea.
Ultrasound Scanners
• Instrument which uses ultrasonic waves for getting images of
internal organs of human body.
• Used in medicine field.
• Ultrasonic waves can be directed at a specific area of the
body.
• The waves travel through the tissues of a body, the waves get
reflected from a region where there is a change of tissue
density.
Ultrasound Scan
Ultrasound Scanners
• The border between two different organs of a body reflect the
waves.
• Scanner provides display of images in a static form or a movie
picture of the inside of the body.
• Ultrasound images are analyzed to obtain information
regarding the internal organs.
Ultrasound Scanners
• Ultrasound – less harmful than X rays
• Technique is an invaluable diagnostic tool for examining fluidfilled organs such as the bladders, kidneys and ovaries.
• used to examine the arterial system, the heart, the pancreas,
the urinary tract, the brain and the spinal cord.
• ECG – echocardiography- ultrasound is used to examine the
heart.
• examination of the foetus during pregnancy to detect
congenial and growth abnormalities.
• used to guide surgical procedures.
DOPPLER EFFECT
Doppler effect is the apparent change in
frequency of wave motion due to the
relative motion between the source and
the observer.
Doppler Effect
• Apparent change in pitch or frequency of sound, whenever
there is a relative motion between the source of sound and an
observer.
• Phenomenon was first investigated by Doppler
• called Doppler effect.
Doppler Effect
• Pitch or frequency of the siren of a speeding fire-engine,
drops abruptly as it passes the observer.
• Both the observers at rest in the sidewalk hear the same pitch
of sound from the fire engine at rest.
Doppler Effect
• Observer towards whom the engine moves feels sound to be
of higher frequency while the other observer feels sound to
be of lower frequency.
• When the engine moves - waves in front appear to be
compressed - hence the observer in front feels the pitch to be
higher.
• waves behind the engine appear to be farther apart- and the
observer feels pitch lower.
Doppler Effect
• Other examples• person standing on a railway platform feels a change in pitch
of the whistle of a train in motion.
• change in pitch results when a moving observer passes a
stationary sounding horn.
Doppler Effect
• Doppler effect in light:
• The speed of light is so high that only celestial bodies or
atomic sources moving at high velocities show pronounced
Doppler effect.
Application Of Doppler Effect
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to determine the velocity of submarines.
to detect vehicles crossing speed limit.
used in tracking the artificial satellites.
study of binary stars, saturn rings, galaxies. Doppler effect is
also used to estimate speeds of stars, galaxies, rotation of
sun’s disc.
Red Shift
• When a source emits light of particular wavelength and the
source is moving away from us, the wavelength appears
longer to us. The color of the light is shifted towards the red
end of the spectrum.
• This effect is known as a red shift.
EXERCISES
Exercises
• What is the frequency range of audible sound?
• The frequency of audible sound is 20Hz to 20,000 Hz.
Exercises
• What are ultrasonic waves?
Ultra sonic Sound is sound which lies above the human audible range .
It lies in the frequency of 20kHz to 5 x 105 kHz.
Range of wavelengths of ultrasonic sound is from 1.65 cm to about 6 x 10-5
cm. It is similar to sound wave in its propagation and speed but has
comparitatively higher energy.
Branch of science that deals with ultrasound is called ultrasonics
Exercises
• List any six uses of ultrasonic waves.
 Understand physical properties of medium.
 manufacture alloys , mixing of immiscible(incapable of mixing) liquids
and to manufacture emulsion for photographic films.
 dry cleaning of clothes to remove grease and dirt.
 detect cracks and flaws in metal moldings.
 welding, local heating and drilling small holes in hard materials.
 serve as insect repellants. Strong beam of ultrasonic waves kills
bacteria. They are used for sterilisation purposes.
Exercises
• What is a Sonar? How does it work?
• Sonar stands for SOund, NAvigation and Ranging.It is a device that
uses ultrasonic waves to measure the distance, direction and speed
of underwater objects.
• Sonar has a transmitter and detector. The transmitter produces and
transmits ultrasonic waves through the water. These waves get
reflected back when they strike an object in water. These reflected
waves (ultrasonic waves)are captured by the detector.
• The time interval between the transmission and reception (t) is
recorded. The velocity of sound through water is V. The distance of
the object (d) is calculated.
d = veloicity(v) X time(t) /2
Exercises
• Using Sonar, ultrasonic waves are emitted at the ocean water
surface. These waves are reflected by the ocean bottom. If the
time interval between the emission of the waves and the
detection of the reflected waves, is 3.5 s, find the depth of the
ocean.
• Velocity of sound in water = 1.5km/s
• Time between transmission and reception = 3.5s
• Depth = distance = velocity X time/2 = 1.5 X 3.5/2= 2.6
Exercises
• What is an ultrasound scanner?
• Ultrasound scanner is an instrument which uses ultrasonic
waves for getting images of internal organs of human body. It
is used in applications in the field of medicine.
Exercises
• Write a note on medical applications of ultrasound waves.
• Ultrasonic waves can be directed at a specific area of the body. As the
waves travel through the tissues of a body, the waves get reflected from a
region where there is a change of tissue density. Scanner provides display
of images in a static form or a movie picture of the inside of the body(baby
foetus ). Ultrasounds are widely used in scanning as they are less harmful
than X rays. The ultrasound images are analyzed to obtain information
regarding the internal organs. This technique is an invaluable diagnostic
tool for examining fluid-filled organs such as the bladders, kidneys and
ovaries.
• Used in examining heart - echocardiography (ECG)- diagonosis of heart
diseases.
• examination of the foetus during pregnancy to detect congenial and
growth abnormalities.
• used to guide surgical procedures.
Exercises
• Explain Doppler effect with an example.
• Doppler effect is the apparent change in frequency of wave motion due
to the relative motion between the source and the observer.
• Pitch or frequency of the siren of a speeding fire-engine, drops abruptly as
it passes the observer. When the engine is moving, waves in front appear
to be compressed and hence the observer in front feels the pitch to be
higher. The waves behind the engine appear to be farther apart. Hence
the other observer feels the pitch to be lower.
Exercises
• Mention three applications of Doppler effect.
• Doppler effect in sound can be used to determine the velocity of
submarines.
• Traffic control authorities use Doppler effect to detect vehicles crossing
speed limit. Radio waves are used for the purpose. Radio waves are sent in
the direction of the speeding vehicle and the reflected waves are received.
The change in frequency of the waves is used to determine the speed of
the vehicle. The instrument used for the purpose is called Radar gun.
• Doppler effect is used in tracking the artificial satellites.
Exercises
• Write a note on application of Doppler effect in astrophysics.
• It is used in the study of binary stars, saturn rings, galaxies. Doppler effect
is also used to estimate speeds of stars, galaxies, rotation of sun’s disc.
• Lines seen in the spectra of galaxies are generally redshifted that is the
wavelength is shifted towards the red end of the spectrum. The amount of
shift depends on the velocity of the source.
• When a source emits light of particular wavelength and the source is
moving away from us, the wavelength appears longer to us. The colour of
the light is shifted towards the red end of the spectrum. This effect is
known as a red shift.
END OF SLIDE
Speeding of Vehicles
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Instrument is called Radar gun
Radio waves are sent in the direction of the speeding vehicle.
The reflected waves are received.
Change in frequency of the waves is used to determine the
speed of the vehicle.
Flaw Detection
Ultrasonic Welding
Working - Ultrasonic Welding
• The two thermoplastic parts to be assembled are placed together, one on
top of the other, in a supportive nest called a fixture.
• A titanium or aluminum component called a horn is brought into contact
with the upper plastic part.
• A controlled pressure is applied to the parts, clamping them together
against the fixture.
Working - Ultrasonic Welding
• The horn is vibrated vertically 20,000 (20 kHz) or 40,000 (40
kHz) times per second, at distances measured in thousandths
of an inch (microns), for a predetermined amount of time
called weld time.
• Produces frictional heat at the interface . When the
temperature at the joint interface reaches the melting point,
plastic melts and flows, and the vibration is stopped. This
allows the melted plastic to begin cooling.
Working - Ultrasonic Welding
• Allow it to cool for some time.
• Once the melted plastic has solidified, the clamping force is
removed and the horn is retracted. The two plastic parts are
now joined as if molded together and are removed from the
fixture as one part.
Working - Ultrasonic Welding