2. Nature of Sound
Sound waves are produced by longitudinal vibrations of
molecules in gases and other media.
This means that as a wave travels through a medium, the
molecules of the medium oscillate to and fro.
The energy of this vibration is carried by the involved
waves, which is brought to our brains for interpretation
as sound.
Sound waves that travel in air
come in contact with our
eardrums causing it to
vibrate.
3. Can sound waves travel in
solid?
Can sound waves travel in
liquid?
If yes give some situations or
examples.
4. Transmission of Sound Waves
The capacity of matter to transmit sound depends
upon its elasticity.
Elastic solid transmit sound well.
Inelastic solid like cloth, rubber, plastic and
sponge transmit sound poorly
7. Why is solid a better sound transmitter than
liquid and gas?
8. Waves are transmitted from
one place to another by the
vibration of particles of the
medium.
We know that particles in a
solid are closer to each other
than the particles in liquid
and in gas.
Therefore, sound waves are
transmitted faster and more
efficiently in solid than in
liquid and in gas.
9. The Velocity of Sound
Thunder is heard few second
after the flask of lightning.
An observer standing at a distance from a gun will
see the flash of light before hearing the sound of
the gunshot
10. An observer standing at a
distance from a fireworks
display will see the flash
of beautiful lights before
hearing the sound of
fireworks explosions.
These show that sound travels slower than
light.
11. The velocity of sound varies in different
media.
It depends on the elasticity and density of
the medium.
In general, the more elastic the medium, the
faster the sound can travel.
The sound can travel faster in a solid
medium than in liquid or gas because the
elasticity of solid is greater than that of
liquid and gases.
13. Assignment:
1. Why sound not transmitted in
a vacuum?
2. A distant lightning can be seen
several seconds before the
accompanying thunder is
heard. Why?
14. Properties of Sound Waves
1. Intensity and Loudness
The quantitative description of the
intensity of sound is determined by a
sound level scale called the decibel
scale.
Sound intensity is the amount of sound
energy flowing each second through a
unit area perpendicular to the direction
of propagation.
17. 2. Reflection of Sound Waves
A sound is reflected when it strikes
another body.
The reflected wave is called an echo.
The reflecting surface has to be at
least 17 meters away from the
source in order for the echo to be
distinct from the original sound.
If the reflecting surface is less 17
meters, the reflected sound wave
just blends with and strengthens the
original sound.
18. The reflection of sound wave is used in
determining ocean depths and the altitude of an
airplane. A sound wave is sent out
from a ship toward the sea
floor.
A wave is reflected from the
bottom of the sea and the
reflected wave is detected
by a receiving device.
Using the recorded elapsed
time and velocity of sound
in water, the ocean depth
may be computed.
19. The airplane altitude, a sonic altimeter is used.
Sonic Altimeter is consists of a sound emitter and
a record that measures the time interval between
the emission of sound and reception of the echo.
The product of the time interval and speed of
sound in air at a given temperature divided by 2 is
the plane’s altitude.
20. Reflected waves can also cause
inconvenience to listeners.
Echoes from smooth curved walls or ceiling
can increase the intensity of sound in certain
parts of the room.
In some cases the problem is due to
reverberation (repeated echoes).
21. 2. Refraction of Sound Waves
Like all types of waves, sound also undergoes
refraction when a change in medium or change
in property of medium takes place.
22. On a clear sunny day, the earth’s
surface is hot.
This causes the temperature of
the air just above the surface of
the earth to rise.
The temperature of the lower layer of air is higher than the
layers above, hence sound should be traveling faster near
the surface of the earth.
This difference in the speed causes the refraction of sound
waves away from the surface.
23. On a clear night the layer of air
nearer the earth’s surface gets
cold faster; hence, the lower
layer of air is colder.
As a result, sound travels faster at the higher layer
than at the lower layer and is refracted toward the
earth’s surface.
24. The sound traveling with
air in the same direction is
bent toward the earth’s
surface.
The sound traveling against
the moving air is bent away
from the earth’s surface.
25. Questions:
1. What is an echo?
2. When an echo considered useful?
3. What happened to the sound waves when
they pass from one medium to another of
different density?
4. Why do sound waves bend
a. away from the surface of the earth
during daytime
b. toward the earth’s surface during
nighttime?
5. Differentiate intensity from loudness.
26. Kinds of Sound Waves
1. Audible Sound Waves
Sound waves that can be detected by human
ear.
A sound waves with frequencies in the range
of 20 to 20,000 Hz can be detected by human
ear.
This range varies from one individual to
another.
27. 2. Ultrasonic Waves
Sound waves with a frequencies above
20,000Hz are called ultrasonic waves.
These waves can also reach human ear but are
not detected.
This ultrasonic sound can be detected by some
animals
Dogs can hear sounds as high as 50,000 Hz,
while bats can hear as high as 100,000 Hz
28. Ultrasonic Waves in the field of Medicine
Ultrasonic waves are used to
probe human organs instead of
X-rays.
Unlike X-rays, ultrasonic
waves does not damage human
tissue.
29. 3. Infrasonic Waves
Sound waves with frequencies below 20 Hz.
Common source of this waves are vibrating
heavy machines, earthquake, thunder, and
volcanic eruption.
These waves are audible but can cause damage
to the human body.
30. How Much Have You Learned?
1. Differentiate ultrasonic from
infrasonic.
2. How is ultrasonic waves
utilized in the field of medicine?
31. Detection of Sound
Human and animals have a
very sensitive detector of
sound – the Ear.
The cross-section of human ear is almost similar to that
of other vertebrates.
32. The ear, which is the peripheral auditory system, is
divided into three parts:
33. The outer ear called the
pinna, collects the sound
waves and concentrates them
into ear canal to a limited
extent.
This canal transmits the
sound waves to the eardrum.
It also protects the eardrum from shock and intrusion by
external objects.
34. Air vibration set the eardrum
membrane in motion which in
turn causes the three little
bones (hammer, anvil, and
stirrup) to move.
These three little bones
convert the small amplitude
vibrations of the eardrum into
larger-amplitude oscillations
and transfer them to the inner
ear through the oval window.
35. Behind this oval window is a
snail-shaped, liquid-filled
organ called cochlea to where
auditory nerves are
connected.
The larger amplitude
oscillations create travelling
waves that are transformed
into impulses sent to the brain
through the auditory nerves.
The brain relates and interprets the sound heard to
those previously experienced.
36. Hearing Damage
1. Noise with an intensity level above 120dB is
considered as an undesirable pollutant in our
environment.
2. Exposure to loud sounds (80dB or above) for a
long period can cause temporary hearing loss.
3. Overexposure to amplified rock music and noise
produced by machineries in factories and other
industrial establishment has been mostly the cause
of hearing damage.
37. 4. Our human ear has a built-in muscular control in
the middle ear.
This limit the potential damage to the ear caused by
sustained loud sound.
But our ear cannot react rapidly to protect itself
against sudden bursts of short but very loud sounds
like gunshots or bomb explosions.
If the sound produced is too loud, it can force an ear
mechanism to go beyond its elastic limit, in this
case, the hearing damage becomes permanent.
38. 5. Permanent hearing loss may also be caused by
physical damage to ear due to diseases, drugs with
side effects, or the natural aging process.
6. Infection of the middle ear due to unhygienic
practices can result to hearing damage.
7. Hearing damage can also occur to a fetus if the
pregnant mother suffered from measles or rubella
within the first trimester of pregnancy.
Rubella can cause malformation of the parts of the
fetus’ inner ear.
39. 8. Drugs such as streptomycin have been found to
cause permanent hearing loss to small children.
Ringing in the ears while the child is under
medication is a symptom of such hearing damage.
Because of this, the use of this drug has been
carefully controlled.
9. A person may also permanently lose his or her
sense of hearing due to normal aging of the auditory
system.