1. SOUND AND
HEARING

2. PRODUCTION OF SOUND
1. Sound is a form of energy that moves in the
form of waves.
2. Vibrations of objects produce sound.
3. Vibrating object transfer the kinetic energy to
air molecules around them. The vibrations of
the air molecules are detected by our
eardrum as sound.
4. Different vibrations produce different types of
sounds.

3. Transmission of Sound
Sound needs a material or medium to travel.
a) Sound can travel through solids, liquids and
gases.
b) Sound cannot be transferred through a vacuum,
because it does not have any particles.
Sound travels at different speeds in different
medium. Sound moves fastest in solid because
the particles are arranged very close to each
other.
Sound moves slowest in gases because the
particles are very far away from each other.

4. Properties of Sound
Sound can be absorbed and reflected when it
hits a surface.
Sound energy can be reflected or absorbed
by the surface of an object.
When sound reaches the surface of a solid,
some waves are reflected, while some are
absorbed.
Absorption of sound makes the reflected
sound weaker than the original sound.

5. Properties of Sound
The intensity of the reflected sound
depends on the amount of sound energy
reflected or absorbed by the surface. When
more sound energy is reflected, the sound
is louder.
The intensity of sound reflected depends
on the nature of the surface
Hard, even and smooth surfaces like plank,
concrete and metal are good sound
reflectors.
Surfaces that are soft and rough like cloth,
carpet and cushion are good sound
absorbers.

6. ECHO
When sound is reflected repeatedly from one surface,
an echo is produced. Echo produces two different
types of sound, i.e the original and the reflected sound.
Both of them can be heard separately.
Echo occurs in enclosed places like caves, tunnels
and halls.
Echo cannot be heard in a small room because the
reflected sound overlaps the original sound.
When an echo is produced, we cannot hear the sound
clearly. Echo and be reduced by putting curtains,
carpets and soft cushions.

7. Pitch and Frequency
1. Frequency of a sound is the number of
vibrations in one second. It is measured in
hertz (Hz).
1 hertz (Hz) = 1 vibration per second
The degree of highness or lowness of a
sound is known as the pitch. The pitch of
sound depends on the frequency. The higher
the frequency, the higher is the pitch.
Therefore, a higher frequency produces a
high-pitched sound.

8. Pitch and Frequency
The pitch of a sound produced by a
vibrating string depends on the;
- Length of the string
A shorter string vibrates faster to produce a higher pitch
- Tension of the string
A higher pitch is produced by a more stretched tight
string , this makes the sound sharper
- Thickness of the string
A thinner string produces a higher pitch

9. Hearing Defect and Ways to
Rectify Them
Hearing defect occur when the sense of
hearing does not function properly
There are different kinds of hearing
defect. To understand the nature of the
defect, we need to identify the part of the
ear that is affected
The earwax in the auditory canal can
block sound waves and causes
temporary loss of hearing

10. Hearing Defect and Ways to
Rectify Them
The ossicles in the middle ear may be fused
together as a result of an infection. This prevents
the ossicles from moving freely. If this conditions is
not treated immediately, it will result in a total
hearing loss.
The inner ear may be damaged by local infections.
Toxins are produced as a result of diphtheria or
scarlet fever. These toxins damage the cochlea
and cause loss of hearing
The sensory cells in the cochlea may be
damaged by exposure to loud sounds. This can
cause hearing loss.

11. Correcting Hearing
Defects
Progress made in science and
technology has enabled us to correct
hearing problems.
Ears, nose and throat specialists may
use syringes and warm water to
remove the wax which is blocking
the auditory canals.
Fused or damaged ossicles can be
replaced by surgery

12. Correcting Hearing
Defects
Punctured eardrums can also be repaired
by surgery. Damaged eardrums can be
repaired or replaced by using
membranes from other parts of the body.
Electronic gadgets can be implanted into
the ears to help some deaf people to
hear better

13. Limitation of Hearing
The human ear has the ability to detect
sounds in the frequency range of 20 Hz
(hertz) to 20 000 Hz. Humans cannot
hear very low frequency or very high
frequency sounds.

14. Limitation of Hearing
The range of hearing varies from one individual
to another.
(a) Children have eardrums that are more elastic.
They hear better
(b) As people age, their hearing worsens. Their
eardrums become less elastic. The range of
sound frequencies that they can detect
becomes narrower. Their ability to hear high-
pitched sounds decreases.
(c) A person exposed to constant loud noises
experiences loss of hearing . His range of
hearing is less than that of a normal person.
(d) Frequencies exceeding 20 000 Hz are called
ultrasonic frequencies. However , some animals
can.

15. Organism Range of sound
frequencies (Hz)
Human being 20-20 000
Whale 10 – 20
Dog 67 – 45 000
Frog 50 – 10 000
Cat 45 – 65 000
Snake 100 - 800
Bat 2000 – 120 000
Dolphin 1000 – 120 000
grasshopper 100 – 15 000

16. Ways to overcome Our Hearing
Limitations
Devices Functions
Amplifier To amplify weak sound signals
Stethoscope Helps doctors to detect soft sounds like
heartbeats of their patients
Loudspeaker - To make announcements during
school assemblies in the school
fields or school hall
Earphone - Converts electrical waves into sound
waves, so that they can be
detected by the ears.
- Enables us to hear something
specific without disturbances from
the noises around us