The document "Sound.pdf" is a concise yet comprehensive study resource focused on the science of sound. It systematically explores the fundamental principles governing sound, beginning with its origins in mechanical vibrations and its subsequent transmission through a medium, whether it be a solid, liquid, or gas. The notes meticulously detail the creation of compressions and rarefactions, which are the regions of high and low pressure, respectively, that constitute a sound wave in air. It elucidates the distinction between longitudinal waves, where particle displacement is parallel to wave propagation (as in sound), and transverse waves, where displacement is perpendicular. A significant portion of the document is dedicated to defining and explaining the key parameters used to characterize sound waves. These include wavelength (the distance between successive compressions or rarefactions), frequency (the number of wave cycles per second, measured in Hertz), time period (the duration of one complete wave cycle), amplitude (the maximum displacement of particles from their rest position, related to the sound's intensity), and speed (the rate at which the wave travels through the medium, which varies depending on the medium's properties). The notes also incorporate graphical representations to aid in visualizing these wave properties. Furthermore, "Sound.pdf" delves into the subjective characteristics of sound as perceived by humans. It elaborates on loudness, which is the perceived intensity of sound; intensity, which is the power per unit area carried by the sound wave; pitch, the perceived highness or lowness of a sound, determined by its frequency; and quality or timbre, the distinctive character of a sound that allows us to differentiate between different instruments or voices. The document also addresses the influence of the medium on the speed of sound, highlighting how sound travels faster in solids than in liquids or gases. The phenomena of reflection, echo, and reverberation are also covered, explaining how sound waves bounce off surfaces and how this affects our perception of sound in enclosed spaces. The document discusses the human auditory range, specifying the frequencies that humans can typically hear, and introduces the concepts of infrasonic sound (frequencies below the human range) and ultrasonic sound (frequencies above the human range). Finally, it briefly touches upon the diverse applications of ultrasonic sound in various fields, such as medical imaging, cleaning, and industrial processes. In essence, "Sound.pdf" provides a structured and informative overview of the essential concepts related to sound.

1. Quick Study Notes Sound 1
We hear sound from various sources, e.g., from
humans, birds, machines, vehicles, TV, radio, etc.
Sound is a form of energy which produces sensation
of hearing in our ears.
Production of Sound
Sound is produced because of vibration in on abject.
In other words, when an object is vibrated, it
produces sound.
For example, Sound can be produced by clapping of
palms.
Propagation of Sound
The source of sound creates a disturbance in the
medium through which it travels. The particles of the
medium do not move forward but the disturbance is
carried forward. A particle of the medium in contact
with the vibrating object is first displaced from its
equilibrium position, it then exerts a force on the
adjacent particle. As a result of which, the adjacent
particle gets displaced from its position of rest.
After displacing the adjacent particle, the firsts
particle comes back to its original position. This
process continues in the medium till the sound
reaches our ear. This is propagation of sound in a
medium
Formation of Compression and
Rarefaction in Air
When vibrating object moves forward in air, it pushes
and compress the air in front of it, creating a
compression which starts to move away from the
vibrating object backwards, it creates rarefaction.
Types of Waves
There are two types of waves
(i) Longitudinal Waves The wave formed ( because of
the oscillation parallel to the disturbance is called
longitudinal wave.
(ii) Transverse Waves The wave formed because of
the oscillation perpendicular to the disturbance is
called transverse wave.
Terms to Describe Sound Waves
Sound waves can be described by its:
1. Wavelength
 The distance covered by a wave during the time
in which a particle of the medium completes one
vibration about its mean position is called
wavelength.
 It is denoted by lambda (λ) .
 Its Sl unit is metre (m).
2. Frequency
 The number of complete waves (or oscillations)
produced in one second is called frequency of the
wave
 It is the number of vibrations that occur per
second. Or the number of the compressions or
rarefactions that cross a point per unit time.
 It is denoted by f.
 Its Sl unit is Hertz (Hz).
3. Time Period
 The time taken by two consecutive compressions
or rarefactions to cross a fixed point is called the
time period of the wave.
 In other words, the time required to produce one
complete wave (or oscillations) is called time
period of the wove
 It is denoted by T.
 Its Sl unit is second (s).
4. Amplitude
 The maximum displacement of the particles of the
medium from their original mean positions on
passing a wave through the medium is called
amplitude of the wave.
 It is denoted by (A). Even if the displacement of
particle is negative, the amplitude of wave is
positive.
 Its Sl unit is metre (m).
5. Speed
 The distance travelled by a wave in one second is
called speed of wave (V).
 The SI unit of speed is metre per second.
 Relationship between speed, frequency and
wavelength is 𝑉 = 𝑓𝜆

2. Quick Study Notes Sound 2
Graphical Representation of
Sound Wave
1. When a sound wave passes through air, the
density of air changes continuously .
2. A sound wave in air has been represented by
means of a density-distance graph as shown
below.
Characteristics of Sound
A sound has four characteristics. These are loudness,
intensity pitch or shrillness quality (or timbre).
1. Loudness
 It is the measure of the sound energy reaching
the ear per second. Greater the sound energy
reaching our ear per second, louder the sound
will appear to be.
2. Intensity
 The amount of sound energy passing each
second through unit area is known as the
intensity of sound. Loudness and intensity are
not the same terms.
 Loudness is a measure of the response of the
ear to the sound. Even when two sounds are
of equal intensity, we may hear one as louder
than the other, simply because our ear
detects it in better way.
 The Si unit of intensity is watt per square
metre (W/m²)
 The intensity of a sound wave in air is
proportional to the
 square of the amplitude of vibrations.
 square of the frequency of vibrations.
 density air.
3. Pitch or Shrillness
 It is that characteristic of sound by which we
can distinguish between different sounds of
the same loudness. Due to this characteristic,
we can distinguish between a man's voice and
woman's voice of the same loudness without
seeing them.
 Pitch of a sound depends on the frequency of
vibration, Greater the frequency of a sound,
the higher will be its pitch.
4. Quality or Timbre
 The quality or timbre of sound enables us to
distinguish one sound from another having
the same pitch and loudness.
 A sound of single frequency is called a tone.
The sound produced due to a mixture of
several frequencies is called a note and is
pleasant in listening too. Noise is unpleasant
to ear. Music is pleasant to ear and it is of rich
quality.
Speed of Sound and Light
The speed of sound in air is about 344 ms-1
at 22°C
and 331 ms-1
at 0°C and the speed of light in air is
300000000 ms-1
or 3x 108
ms-1
. Thus, speed of light is
very high as compared to the speed of sound.

3. Quick Study Notes Sound 3
Speed of Sounds in Different
Media
The speed of sound depends on the properties of
medium through which it travels and the temperature
of the medium. It decreases when we go from solid to
gaseous state.
Speed of Sound in Different Media at 25°C
Substance Speed (m/s)
Solids
Aluminium 6420
Nickel 6040
Steel 5960
Iron 5450
Brass 4700
Glass (Flint) 3980
Liquids
Water (Sea) 1531
Water (Distilled) 1498
Ethanol 1207
Methanol 1103
Gases
Hydrogen 1284
Helium 965
Air 346
Oxygen 316
Sulphur Dioxide 213
Reflection of Sound Wave
When sound waves strike a surface, they return back
into the same medium. This phenomenon is called
reflection.
Laws of Reflection
i. Angle of incidence is equal to the angle of
reflection.
ii. The incident wave, the reflected wave and the
normal, all lie in the same plane.
Echo
 The repetition of sound caused by the reflection
of sound waves is called an echo,
 The sensation of sound persists in our brain for
about 0.1 s. Thus, to hear a distinct echo, the time
interval between the original sound and the
reflected. One must be at least 0.1 s.
 The distance travelled by the sound in 0.1 s =
Speed x Time = 344 x 0.1 = 34.4 m.
 So, echo will be heard, if the minimum distance
between the source of sound and the obstacle is
.
= 17.2 m
Reverberation
The persistence of a sound in a big hall due to
repeated reflections from the walls, ceiling and floor
of the wall is known as reverberation.
Uses of Multiple Reflection of Sound
i. Megaphones and Horns
 Megaphone is a large cone shaped device used
to amplify and send the voice of a person in
particular direction who speaks into it.
 When a person speaks into the narrow end of
the megaphone tube, the sound waves
produced are prevented from spreading by
successive reflections from the wider end of the
megaphone tube, hence sound of his voice can
be heard over a longer distance.
ii. Stethoscope
 It is a medical instrument used by doctors to
listen to the sound produced within the heart
and the lungs in human body. The sound of
heartbeats (or lungs) reaches the doctors ears
by the multiple reflections of sound waves
through the stethoscope tube.
iii. Sound Board
 It is a concave board (curved board) placed
behind the stage in big halls, so that sound after
reflecting from sound board, spreads evenly
across the width of the hall.
 Generally, the ceilings of the concert halls,
conference halls and cinema halls are also
curved, so that sound after reflection reaches
all corners of the hall
Range of Hearing
 The average frequency range over which the
human ear is sensitive is called audible range. The
audible range of sound for human beings is from
20 Hz to 20000 Hz (20 kHz).
 Children under the age of Sand some animals such
as dogs can hear up to 25000 Hz. As people grow
older, their ears become less sensitive to higher
and lower frequencies.

4. Quick Study Notes Sound 4
Infrasonic Sound
Infrasonic waves have frequencies below 20 Hz and it
is low frequency sound waves. These waves are
generated by natural and human made sources.
Ultrasonic Sound
 The sound of frequencies higher than 20000 Hz
are called ultrasonic sound or ultrasounds which
cannot be heard by human beings. Dogs can hear
ultrasonic sound of frequencies up to 50000 Hz.
 This is why, dogs are used for deflective work by
the police. Bats, dolphins and porpoises can
produce ultrasonic sounds.
 Some of the important applications of ultrasonic
sound are given below
i. Used in investigation of internal organs of
human body.
ii. Used to clean parts located hard to reach
places such as spiral tubes.
iii. Used in detecting flaws (Cracks) in industries.