Sound is produced by vibrations that travel as sound waves through a medium such as air or water. When these vibrations reach the ear, they are interpreted by the brain as sound. Sound waves are caused by the vibrations of objects and consist of areas of high and low pressure called compressions and rarefactions. Sound can reflect off surfaces, and the reflection of sound follows the laws of reflection where the angle of incidence equals the angle of reflection. Reflections of sound cause echoes and reverberation. The human ear can detect sounds between 20 Hz to 20 kHz, known as the audible range. Ultrasound refers to sounds above this range and infrasound refers to sounds below. Ultrasound has many applications including

1. SOUND
Aakanksha sharma
IX-F

2. WHAT IS SOUND?
All sounds are vibrations traveling through the air as sound
waves. Sound waves are caused by the vibrations of
objects and radiate outward from their source in all
directions. A vibrating object compresses the surrounding
air molecules (squeezing them closer together) and
then rarefies them (pulling them farther apart). Although
the fluctuations in air pressure travel outward from the
object, the air molecules themselves stay in the same
average position. As sound travels, it reflects off objects in
its path, creating further disturbances in the surrounding
air. When these changes in air pressure vibrate your
eardrum, nerve signals are sent to your brain and are
interpreted as sound.

3. PRODUCTION OF SOUND
Sound is produced when something vibrates. The
vibrating body causes the medium(water, air, etc)
to vibrate around it. Vibrations in air are called
travelling longitudinal waves, which we can hear.
Sound waves consist of areas of high and low
pressure called COMPRESSION and RAREFACTION
respectively.

4. PROPAGTAION OF SOUND
Sound is a sequence of waves of pressure which
propagates through compressible media such as air
or water. (Sound can propagate through solids as
well, but there are additional modes of propagation).
During their propagation, waves can be reflected,
refracted, or attentuated by the medium.

5. CHARACTERISTICS OF SOUND
We can describe a sound wave by-
•FREQUENCY in a sound wave refers to the rate of the vibration of the
sound travelling through the air. The SI Unit for Frequency is hertz.
•AMPLITUDE refers to the distance of the maximum vertical
displacement of the wave from its mean position. Larger the
amplitude, higher the energy.
•SPEED of sound is the distance travelled per unit time by a sound
wave as it propagates through and elastic medium.

6. REFLECTION OF SOUND
The reflection of sound is similar to the reflection of light as it follows the laws of
reflections, where the angle of incidence is equal to the angle of reflection and
the incident sound, the reflected sound and the normal lie in the same plane. In
order for reflection of sound to occur, the surface can be either rough or polished
and of considerably large size.
Laws of Reflection of Sound-
•The angle of incidence is always equal to the angle of reflection.
•The incident sound wave, the reflected wave and the normal at the point of
incidence are in the same plane.

7. APPLICATION OF REFLECTION OF SOUND
ECHO
The sound heard after reflections from a rigid surface such as a cliff or a wall is
called echo creating a persistence of sound even after the source of sound has
stopped vibrating. Echo is used by bats and dolphins to detect obstacles or
navigate. Echo is derived from the Greek word which means Sound. Simply, Echo
can be also defined as: The Phenomenon in which the sound wave is reflected and
hence arrives to the listener after some time delay after the direct sound.
if we consider the single reflection of the sound source then it is called true echo.
Sonar is based on the concept of Echo. The device is attached to the ship at its
base. Then the sound wave is originated from the sonar. The sound wave travels to
the bed of the sea, and is reflected from the sea bed and is received by the sonar
receiver. This distance traveled is equal to the depth of the sea. It is used to see the
obstacle also. It consists of a transmitter and a receiver.

8. APPLICATION OF REFLECTION OF SOUND
REVERBERATION
Reverberation is the same as echo but the distance here is less. The
distance between the source of the sound and the obstacle by which it is
reflected is less in Reverberation.
Singing in the shower is an example of reverberation. The walls are close
to us and hence it is observed. Hence now the two waves are heard as a
prolonged sound wave.
The walls should be less than 17 meters.

9. APPLICATION OF REFLECTION OF SOUND
Whispering gallery :
The famous whispering gallery at St. Paul’s Cathedral is a circular shaped chamber
whose walls repeatedly reflect sound waves round the gallery, so that a person
talking quietly at one end can be heard distinctly at the other end. This is due to
multiple reflections of sound waves from the curved walls.
Stethoscope :
Stethoscope is an instrument used by physicians to listen to the sounds produced by
various parts of the body. It consists of a long tube made of rubber or metal. When
sound pulses pass through one end of the tube, the pulses get concentrated to the
other end due to several reflections on the inner surface of the tube. Using this
doctors hear the patients’ heart beat as concentrated rays.

10. RANGE OF FREQUENCIES
The human ear is sensitive to sound waves of
frequency between 20 Hz to 20 kHz. This range is
known as AUDIBLE RANGE and its waves are known as
AUDIBLE WAVES
Eg. Waves produced by vibrating sitar, guitar, organ
pipes, flutes, shehenai, by human vocal chords, and
diaphragms of loudspeakers etc.
A longitudinal wave whose frequency is above the
upper limit of audible range, i.e. 20 kHz, is called as
ULTRASONIC WAVES. I is generated by very small
sources.
Eg. quartz crystal
A longitudinal elastic wave whose frequency is below
the audible range, i.e. 20Hz, is called INFRASONIC
WAVE . It is generally generated by a large source
Eg. Earthquake, thunders, volcanoes, produced by
vibrating heavy machineries, etc.

11. ULTRASOUND
Sound waves with frequencies higher than the upper
audible limit of human hearing are called ultrasound.
The concept of ultrasound is used in many different fields
such as navigation, medicine, imaging, cleaning, mixing,
communication, testing etc. Even in the nature, bats and
porpoises use ultrasound for the location of prey and
obstacles

12. USES OF ULTRASOUND
• CLEANING
In objects with parts that are difficult to reach, for example
spiral tubes and electronic components, the process of
ultrasonic cleaning is used. Here, the object is dipped in a
solution of suitable cleaning material and ultrasonic waves
are passed into it. As a result of this, high frequency waves
are generated that cause the dirt and grease to detach from the surface.
• DETECTION OF CRACKS
Ultrasound is used to detect cracks in the metallic components
that are used in the construction of high rise structures such as
buildings and bridges. They generate and display an ultrasonic
waveform that is interpreted by a trained operator, often with
the aid of analysis software, to locate and categorize flaws in
test pieces. High frequency sound waves reflect from flaws in
predictable ways, producing distinctive echo patterns that can
be displayed and recorded by portable instruments.

13. •ECHOCARDIOGRAPHY
In the process of electrocardiography,
the ultrasonic waves are used to form an Image of
the heart using reflection and detection of these
waves from various parts.
•ULTRASONOGRAPHY
Medical ultrasound is a diagnostic imaging technique
based on ultrasound. It is used for the imaging of
internal body structures such as muscles, joints and
internal organs. Ultrasonic images are known as
sonograms. In this process, pulses of ultrasound are
sent to the tissue using a probe. The sound echoes
off the tissue, where different tissues reflect sound
varying in degrees. These echoes are recorded and
displayed an image.

14. •LITHOTRISPY
Ultrasonic waves are used to break
stones in the kidney. High-energy sound
waves are passed through the body
without injuring it and break the stone
into small pieces. These small pieces
move through the urinary tract and out
of the body more easily than a large stone.
•SONAR
SONAR, sound navigation and ranging
is a technique in which sound waves
are used to navigate, detect and
communicate under the surface of the water.

15. •ECHOLOCATION
Echolocation is the process where sound waves
and echoes are used to determine objects in
space. Echolocation is used by bats to navigate
and find their food in the dark. Bats send out
sound waves from their mouth and nose, which
then hit the objects in their vicinity producing
echoes, which are then received by the bats.
The nature of the echo helps them determine the
size, the shape and the distance of the object.
•Urology
It hepls in measuring blood flow through
the kidneys and seeing kidney stones, also
it helps in detecting prostate cancer early

16. THANK YOUU!
Aakanksha Sharma
IX-F