Sound is produced by vibration and requires a medium like air, water or solid material to propagate. When a vibrating source produces sound waves, the medium's particles vibrate in compressions and rarefactions that transfer energy as the wave moves. Characteristics of waves include amplitude, wavelength, frequency and velocity. The human range of hearing is 20-20,000 Hz but ultrasound above 20 kHz and infrasound below 20 Hz also exist and have applications like echolocation and earthquake detection.

1. PROPAGATION OF SOUND
WAVES
By karthik

2. WHAT IS SOUND AND EXPERIMENTS
ON VIBRATION
• Sound is a form of energy that produces the sensation of hearing
• Sound is produced when a body is vibrating
• Experiment 1: is a string of a guitar is plucked the string starts vibrating and sound is heard
• Experiment 2: Take thin wire stretch it between 2 nails. place a small piece of paper on the wire
as a rider. pluck the string near the rider it is shown the rider flies off and the string starts
vibrating and sound is heard.
• Experiment 3: Take a tuning fork and strike to a rubber pad. Then take it near a ball suspended
by a thread. when the vibrating tuning fork is brought close to the ball the ball moves away and
sound of vibrating tuning fork is heard.
• From the above experiments we can prove that sound is produced vibration and sound ceases
when vibration stops.

3. MEDIUM OF SOUND PROPAGATION
• Sound produced by a vibrating body travels form one place to the other through vibrations of
particles of the medium in wave form.
• Thus, Sound requires a material medium to travel from one place to the other.
• Bell jar Experiment :Take an electric bel and place it in an airtight glass bell jar. Connect the
vacuum pump to the bell jar. First turn on the switch and we can see the hammer hitting the
gong and sound being produced. Then when we suck all the air out of the bell jar and turn the
switch on again. We can see the hammer hit the gong so we no vibrations are produced, but
hear no sound.
• Sound cannot travel in a vacuum.
• Light does not require a medium for its propagation and can propagate through vacuum as
well.

4. OBJECTIVES OF THE SOUND
MEDIUM
• The particles should be capable of vibrating about their mean positions.
• The medium must remain unchanged (inertia) so that its particles may store mechanical
energy for a given time.
• The medium must remain frictionless so that there is no loss of energy in propagation of
sound through it.
• Sounds can propagate not only in gases but in solids and liquids as well.
• This is decreasing order of sound in medium.
• Some materials propagate sound (air) and some materials absorb sound. (thick curtains)
solids liquids gases

5. PROPAGATION OF SOUND IN A
MEDIUM
• When we talk depending on the direction we talk sound is transmitted
i. There are fast moving particles that make up air
ii. When we talk the sound wave produced goes through the air
iii. The sound wave groups the particles into 2 groups
iv. The particles which are closely packed are called compressions
v. The space between the waves which particles are far apart and rare are called rarefactions
characteristics of wave motion----

6. TERMS OF WAVE MOTION
• Amplitude is the maximum extent of a
oscillation, measured from the position of
equilibrium.
• Time period is the time taken by a particle of a
medium to complete one vibration.
• Frequency is the number of vibrations made by
a particle of medium in 1 second.
• Wavelength is the distance travelled between 1
time period of vibration of particle of the
medium
• Wave velocity is the distance
travelled by a wave in 1second.

7. TYPES OF GRAPHS
Displacement time graph Displacement distance graph
• The variation of displacement with time
• for a particle of the medium at a given position
• when a wave propagates through the medium
• A Displacement – Distance graph shows the position
of each particle in a wave relative to its distance from
a reference point.
• The distance between 2 successive crest or trough is
the wavelength.
• The maximum displacement of the particles from the
equilibrium position is the amplitude.

8. RELATION BETWEEN WAVELENGTH
WAVE VELOCITY AND FREQUENCY
• 𝑤𝑎𝑣𝑒𝑙𝑒𝑔𝑛𝑡ℎ 𝜆 = 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑡𝑟𝑎𝑣𝑒𝑙𝑙𝑒𝑑 𝑏𝑦 𝑡ℎ𝑒 𝑤𝑎𝑣𝑒 𝑖𝑛 𝑜𝑛𝑒 𝑡𝑖𝑚𝑒 𝑝𝑒𝑟𝑖𝑜𝑑
• 𝑤𝑎𝑣𝑒𝑙𝑒𝑔𝑛𝑡ℎ 𝜆 = 𝑤𝑎𝑣𝑒 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑥 𝑡𝑖𝑚𝑒 𝑝𝑒𝑟𝑖𝑜𝑑
• 𝑤𝑎𝑣𝑒𝑙𝑒𝑔𝑛𝑡ℎ 𝜆 = 𝑉 𝑥 𝑇 (𝜆 = 𝑉𝑇)
• 𝑏𝑢𝑡 𝑡𝑖𝑚𝑒 = 𝑜𝑛𝑒 𝑏𝑦 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 𝑇 =
1
𝑓
• 𝑉 𝑥
1
𝑓
= 𝜆
• 𝑉 = 𝑓𝜆
• Wave velocity = frequency x wavelength

9. SOUND AND HUMANS
• 20 to 20,000 Hz is the audible range
• our hearing is most sensitive in the 2000 - 5000 Hz frequency range.
• Your ear can stand a maximum of 85 decibel as an average noise level over a day, before it is
damaged by the noise.
• The sound level of normal conversation is between 50 and 65 decibels, speaking generally.

10. COMPARISON OF FREQUENCIES
ultrasonic
Sound of above 20,000 Hz is called
ultrasound.
Energy carried by the ultrasound is
very high
Ultrasound can travel along a well
defined strait path. It does not bend
appreciably at the edges of an
obstacle because of its small
wavelength.
Bats avoid obstacles in their path by
producing and hearing the
ultrasonic waves which returns after
striking the obstacle. By hearing the
reflected sound they judge their
direction of the obstacle.
Ultrasound is used for drilling holes
or making cuts of desired shape in
materials
sonic
Frequencies in the range 20Hz to
20kHz is called the sonic or audible
sound.
infrasonic
sound waves below the frequencies
of audible sound, and nominally
includes anything under 20 Hz.
soot cleaners and for integrity
monitoring.
Used to detect earthquakes
The waves are efficiently reflected
from the surface and may be
transmitted by multiple “bounces”
to more distant regions.
For example, infrasound
detected by us from
Mexican earthquakes would have
made about 10 bounces to reach
the detectors