3. PROPAGATION OF SOUND
•Sound is produced by vibrating objects.
•Sound is transmitted through a medium.
•Medium can be solid, liquid or gas
•It moves from point of generation to the
listener.
•When the object vibrates, the particles in the
medium around it start vibrating.
4. PROPAGATION OF SOUND
•There is no movement of the particles, they
don’t travel.
•The particles are displaced from their
equilibrium state.
•The particle exerts force on the adjacent
particle.
•The adjacent particle gets displaced while the
previous particle returns to original position.
6. SOUND WAVE
•Wave is a disturbance that moves through a
medium.
•The wave is created when particles set
neighbouring particles into motion.
•Since the particles of the medium are in motion,
Sound wave is a mechanical wave.
8. MECHANICS OF SOUND WAVE
•Air is the most common medium through which
the sound travels.
•Forward movement of vibrating object compress
the air, creating high pressure, this is called
Compression (C).
•The compression moves away from the vibrating
object.
10. MECHANICS OF SOUND WAVE
•When the vibrating object moves backwards it
creates low pressure called the Rarefaction (R).
•Pressure is related to the number of particles in
the medium in a given volume.
•The denser the medium the more the pressure.
•Thus sound propagation is a propagation of
density variation or pressure variation in the
medium.
12. SOUND AND MEDIUM
•Sound being a
mechanical wave
needs a medium.
•It cannot travel in
vacuum.
13. SOUND – LONGITUDINAL WAVE
•Sound waves are longitudinal waves as
:-
•The individual particles move in a
direction parallel to the propagation of
disturbance.
•They oscillate back and forth about their
position of rest.
16. WAVELENGTH DEFINED
•In case of Sound waves the distance between two
consecutive Compressions (C) or two consecutive
Rarefaction (R) is called the wavelength.
•Wavelength is denoted by Lambda.
•The SI unit of wavelength is meter (m)
18. FREQUENCY DEFINED
•Frequency tells us how frequently an event
occurs.
•In case of Sound waves it is the number of
Compressions (C) or number of Rarefaction (R)
per unit of time is called the frequency of the
sound wave.
•Frequency is denoted by nu.
•The SI unit of frequency is hertz (Hz)
20. TIME PERIOD DEFINED
•The time taken by two consecutive
Compressions (C) or Rarefaction (R) to cross a
fixed point is called the time period of the wave.
•Time period is denoted by T.
•The SI unit of Time period is second (s).
•Frequency and Time period are related as
• Frequency = 1/ T
22. PITCH OF SOUND
•The faster the vibration of the source, higher is
the frequency and thus higher the Pitch.
•A high pitch sound corresponds to more number
of Compressions (C) and Rarefactions (R) passing
fixed point per unit time.
24. AMPLITUDE DEFINED
•The magnitude of maximum disturbance in the
medium on either side of the mean is called
Amplitude.
•Amplitude is denoted by A.
•The Loudness or Softness of sound is
determined by its Amplitude.
•It depends on the force used to produce the
vibration.
26. TONE, NOTE, NOISE DEFINED
•A sound of single frequency is called Tone.
•A sound of mixed frequency is called Note
•What is pleasant to listen is called Music.
•Noise is unpleasant to the ear.
27. SPEED OF SOUND IN DIFFERENT
MEDIUM
•The sound propagates through a medium at a
finite speed.
•The speed of depends on the properties of the
medium. It travels faster in a denser medium.
•The speed of sound depends on the temperature
of the medium. It increases with rise in
temperature.
28. 316 346
965
1284
1103 1207
1498 1531
3980
5950 5960
6420
0
1000
2000
3000
4000
5000
6000
7000
Oxygen Air Helium Hydrogen Methanol Ethanol Distilled
Water
Sea Water Glass
(Flint)
Iron Steel Aluminium
Speed of Sound in Different Medium
29. REFLECTION OF SOUND
•Sound follows the same laws of reflection as
light.
•The angle of incident sound wave and the
reflected sound is equal with the normal to the
reflecting surface.
•The incident wave the normal and the reflected
wave lie on the same plane.
31. ECHO
•Echo is the reflection of Sound from buildings
and mountains.
•To hear an Echo the difference between the
initial sound and the reflected sound should be
at least 0.1 sec.
•Mathematically this distance travelled by sound
should be at least 34.4 m on an ambient
temperature of 22 degrees centigrade.
33. REVERBERATION
•Repeated reflection of sound that results in its
persistence is called reverberation.
•Excessive reverberation prevents perception of
sound.
•Reverberation is controlled by covering the roof
and walls of auditoriums with sound absorbing
material.
•Fibreboard, rough plasters, cardboards, and
36. USES OF MULTIPLE REFLECTION -
SOUND
•Megaphones are used to amplify the sound.
•Doctors use Stethoscope which has pipes where
multiple reflections take place.
•Curved ceilings of cinema halls are used to
ensure that sound reaches to all the audience.
•Soundboards are used behind the stage to reflect
the sound.
38. RANGE OF HEARING
•Audible range for human beings is from 20 Hz
to 20000 Hz.
•Younger children and few animals hear beyond
this range as well.
•Sound below 20 Hz is called Infrasonic. (Rhinos,
Whales)
•Sound beyond 20000 Hz is called Ultrasonic.
(Bats, Dolphins)
40. APPLICATIONS OF ULTRASOUND
•Cleaning of hard to reach places of machines.
•Detect cracks and flaws in metal blocks.
•Medical application in echocardiography.
•Ultrasound imagery of internal organs of human
body.
•Removal of kidney stones by breaking them with
ultrasound.
42. SONAR
•SONAR stand for SOund Navigation And
Ranging.
•It uses ultrasonic waves to measure distance,
direction and speed of underwater objects.
•It has a transmitter and a detector collectively
called Transducer.
•Mathematics of distance calculation is 2d = v x t
