Vibration produces sound waves that propagate as longitudinal waves through a medium such as air. When an object vibrates, it causes disturbances in the surrounding air particles that move away as a sound wave. Sound waves travel through air and other media by particles colliding and vibrating in the direction of propagation. Sound is generated by various means including plucking, striking, rubbing and blowing objects, and is detected when the sound waves reach the ear.

2. Sound is produced by a vibrating body
When a tightly stretched band is plucked, it
vibrates and produces sound.
When it stops vibrating, it does not produce
any sound.
A vibrating body is a source of sound.
Vibrating object produces sound.
Vibration means object a kind of a rapid to
and fro motion.

3. PRODUCTION AND PROPAGATION OF SOUND WAVES
By plucking, striking, rubbing and blowing we
can produce sounds. Scratching and shaking different
objects are other ways of producing sounds.
These vibrations disturb the air particles close to
the vibrating object, which in turn pass it on to other
particles.
Each to and fro movement causes a disturbance
of the air particles so that the continuously vibrating
body causes a series of disturbances. The series of
disturbances move through the atmosphere from the
source.

4. Production of Sound
Sound has great importance in our daily life.
Sound makes it possible for us to communicate
with one another through speech. It enables us to share our
thoughts and ideas with others.
• Musical sound gives us pleasure.
• Radio and television sound gives us information and
entertainment.
• Horn sounds of vehicles alert us and keeps us safe
on the road.
Ex : Bell , Drums , Alarm Clock, Whistle, Horn

5. Propagation of Sound
Sound travels through a medium from the
point of generation to the listener. Sound waves
travel along the to and fro movement of the
vibrating objects that produce them.
Medium :
The matter or substance through which
sound is transmitted is called a medium. It can be
a solid, liquid or gas.

6. Sound Needs a Medium to Travel:

7. Characteristics of
Sound wave

9. Longitudinal Waves
If the particles of a medium vibrate in a
direction, parallel to or along the direction of
propagation of wave, it is called longitudinal wave.
Ex: Sound waves

11. Compression :
Is the area with maximum pressure
Rarefaction
Is the area with minimum pressure.

12. Transverse Waves
If the particles of the medium vibrate in a
direction, perpendicular to the direction of
propagation, the wave is called transverse wave.
Ex: Water waves, Vibrations of stretched
string

13. Crest :
The maximum displacement along the upward
direction.
Trough :
The maximum displacement along the
downward direction.

15. Reflection of Sound
Echo
The sound waves produced by us bounce
back or reflected from the forest or mountain or
buildings come to our ears as echo.

16. For example, the sound uttered by a person
may be heard two or three times after the
reflection from an object.
For hearing echo , the barrier reflecting the
sound should be at least a distance of 17m.
The sensation of sound persists in our ear for
1/10th of a second.
So to hear echo, the sound after reflection
should fall on the eardrum after 1/10th of a second.

17. Reverberation
The repeated reflection that results in the
persistence of sound.
In an auditorium, big hall, theaters and audio
recording theatres, etc.., the excessive
reverberation is highly undesirable.
To reduce reverberation, the roof and walls
of auditorium are generally covered with sound
absorbing materials like compressed fibre board
rough plaster or draperies.

18. Range of Hearing

20. Sounds of frequencies above 20000 Hz are
known as Ultrasonic.
Ex: Sometimes sound produced by bats,
dolphins are ultrasonic.
Sounds of frequencies below 20 Hz are
known as Infrasonic.
Ex: Sometimes sound detect by cows,
elephants are infrasonic.

21. We cannot hear ultrasonic and infrasonic. But
certain animals can produce and detect ultrasonic
and infrasonic.
Audible range of Sound ( in Hertz ) for Human and certain
animals
Human – 20 – 20,000
Elephant - 16 – 12,000
Cow - 16 – 40,000
Cat - 100 – 32,000
Dog - 40 - 46,000
Rabbit - 1000 – 1,00,000
Bat - 1000 – 1,50,000
Dolphins - 70 – 1,50,000
Seal - 900 – 2,00,000
Turtle - 20 – 1000
Frog - 100 - 3000

22. Noise

23. Noise
The unpleasant sound is called as
noise.
Ex: horns of buses
Music
Musical sound is one which is
pleasing to the ear.
Ex: Sound produced by a
harmonium is musical sound

25. Harmful Effects of Noise Pollution :
* Sudden high noise level can damage to
the eardrum.
* The Presence of excessive noise in the
surroundings may cause many health related
problems.
* Also disturb sleep, increases stress and
causes headache. It can lead to nervous tension
and increase of blood pressure

27. T.V and musical
instruments should be
played at low volume
We must control the
source of noise
Cars and other vehicles
should not produce loud
sounds or use of
automobiles horns should
be minimised
The use of loudspeakers at
function should be
stopped.
To control
noise pollution

28. Application of Ultra Sound
Ultra sounds are high Frequency waves. Ultra
Sounds are able to travel along well defined paths
even in the presence of obstacles. Ultra sounds are
used extensively in industries and for medical
Purposes.
* Ultra sounds is generally used to clean parts
located in hard-to-reach places, for example, spiral
tube, odd shaped parts, electronic components etc..
* Ultra Sounds can be used to detect cracks
and flaws in metal blocks.

29. Application of Ultrasound
* SONAR (SOund Navigation And
Ranging)
* Ultra Sonography

30. SONAR (SOund Navigation And Ranging)
The word “SONAR” is an abbreviation
for “SOund, Navigation And Ranging”.

31. A sonar consists of a transmitter, detector,
and display. The transmitter produces and
transmits pulses of ultrasonic waves. These waves
travel through water and after striking the
underwater object such as the sea bed or a shoal of
fish, get reflected and are received by the
Detector.
The detector converts the ultrasonic waves
into electrical signal which are appropriately
interpreted.

32. Echo Ranging :
Set the time interval between transmission and
reception of ultrasound is ‘t’ speed of sound
through water is ‘v’ total distance travelled (to &
fro) is ‘2d’.
2d = v X t

33. Example:
Let us assume that the time interval between
the transmitted pulse and the reflected pulse is
3seconds and that the speed of sound in water is
1440m/s the distance to the object would be:
d= (1440 m/s X 3 seconds) /2
This method is called echo ranging. It is used
to determine the depth of the sea and to locate under
water hills, submarine, icebergs, sunken ship, etc.

34. Ultra Sonography
‘Ultra sonic waves’ can be used to visualize
inner organs of the human body.
Pulses of ultrasonic waves are passed through
parts of the body which get reflected by organs.
When several pulses are sent and received,
it is possible to build a picture of the object
reflecting the wave pulses. This is called ultra
sonography.

35. It is used to visualize different organs
especially the human foetus inside the uterus before
the baby is born. Doctors can make out the
condition of the baby by looking at the ultra
sonographic image.
A picture of a medical professional carrying
out an ultrasonic scan and an image of the baby in
the uterus is shown below.

36. Doppler Effect :
The Phenomenon of the apparent change in the
frequency of the source due to relative motion
between the source is called as Doppler’s effect.
Christian Johann Doppler (1803 – 53)
In 1842, Doppler published the paper
“Concerning the Coloured Light of Double
Stars”, which contained his first statement
describing the Doppler Effect.
He theorized that since the pitch of sound
from a moving source varies for a stationary
observer, the colour of the light from a star
should alter, according to the star’s velocity
relative to Earth.

37. Uses of Doppler Effect in Sound
RADAR (Radio Detection And Ranging) Doppler
effect principle is used in RADAR to determine the
velocities and movement of submarines and aircrafts.
The Doppler effect shift of radar waves are used
in airports to find the height, speed and distance
approaching aircrafts.
Bats send out and receive ultrasonic waves
reflected by the prey and obstacles. Bats detect the
location, distance and movement of the prey by the
Doppler shift.