CHETTINAD VIDYASHRAM,R.A.PURAM,CHENNAI.

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CLASS VIII-PHYSICS NOTES-FILE Q/A

HALFYEARLY PORTION-Chapter 13.SOUND(page no.157 in NCERT Textbook)

1.Define the terms(a)Sound (b)Vibration

• A sound is a form of energy that is produced when air molecules vibrate in a particular pattern
called waves. Hence, the sound is a wave.

• Vibration can be described as a back and forth motion of an object.

• Depending upon the vibrations, a sound is produced. Sound cannot be produced without any
vibration.

2.How do humans produce sound?

1. Human beings have a voice box or larynx which is present in their throat on the upper side of the
windpipe.

2. The larynx has two vocal cords which have a narrow slit between them so that air can pass through
it.

3. As the lungs throw the air out of the windpipe, it passes through the slit and hence allows the
production of sound as the vocal cords start vibrating.

4. The vocal cord has folded muscles which also play a role in the production of sound.

5. Their thickness and tightness describe the quality or type of the voice a person has.

6. The vocal cords in males are of length 20 mm and females have 15mm long vocal cords. Children,
on the other hand, have very short length vocal cords. Hence, the voices, their quality and their
type are always different in women, men and children. (diagram should be drawn in LHS-unruled
side)

3.Explain briefly the characteristics of a sound

wave.
4. How does sound travel in a medium?
• Sound needs some vibration of molecules to travel.

• Solids, liquids and gases all have molecules present in them which allow the propagation of
sound.

• These molecules or particles in solids, liquids and gases are packed in varied ways.

• Solids have tightly packed particles in them and hence they allow fast propagation of sound
through them as the vibrations can be carried easily from one particle to another.

• Liquids have slightly loosely packed particles and hence it takes a little time for sound to travel
in water or through a liquid.
• Gases have completely loosely packed particles and hence sound takes the most time in
travelling through the air.

5.Describe the structure and working of the human

ear.
Structure of Human Ear:The human ear can be divided into three main parts :Outer ear, middle
ear and inner ear.

Outer Ear: The outer ear is outside the body and is also called pinna. It extends into the ear
canal. Ear canal is filled with air.Middle Ear: The middle ear is composed of the ear drum or
tympanum( it is an elastic membrane, circular in shape) and three delicate bones namely, the
hammer, the anvil and the strirrup.Inner Ear: The inner ear has a coiled tube called cochlea and
The cochlea is filled with liquid. Tiny hairs in this liquid filled tube pick up vibrations from the
middle ear.Working of Human Ear: The outer ear called pinna collects the sound waves. The
sound waves passes through the ear canal to a thin membrane called eardrum. The eardrum
vibrates. The vibrations are amplified by the three bones of the middle ear called hammer, anvil
and stirrup. The middle ear then transmits the sound waves to the inner ear. In the inner ear the
sound waves are converted into electrical signals by the cochlea and sent to the brain through
the auditory nerves. The brain then interprets the signals as sound and we hear the sound.
 7. Tabulate the differences between music and
noise.
MUSIC NOISE
1.Produced when vibrations 1.Produced when vibrations
are periodic and continuous are non-periodic and
discontinuous

2.There are no sudden 2.There are sudden changes in

changes in loudness and loudness and pitch
pitch

3.Pleasant ,smooth and 3.Unpleasant,jarring and

agreeable to the ear disagreeable to ear

4.Sound produced by musical 4.Sound from horns of

instruments vehicles

8.What is noise pollution?What are the effects

of noise pollution?List some measures to control
the noise pollution.
• Noise pollution can be defined as the presence of undesirable and unpleasant sounds in the earth's
environment.

• Human beings can bear sounds ranging up to 85 decibels only. Above that, any noise can damage
our hearing power.

Effects of Noise Pollution

1. Excessive noise in the surroundings can lead to serious health problems such as hypertension, lack of
sleep or insomnia, anxiety, lack of memory, stress, irritation and even nervous breakdown.

2. It can lead to temporary or permanent hearing loss in human beings as well as animals.

3. Excessive noise leads to increased blood pressure. It increases cholesterol levels in the blood and
therefore increases the chances of cardiovascular diseases in a person.

Prevention of Noise Pollution

1. Factories and other industries should be set up at a distance from residential areas.
2. Silencing devices should be incorporated into heavy vehicles such as aircraft, industrial equipment,
machinery and other home appliances.

3. We should always play television, radio and other music systems at a low sound so that it does not
harm the neighbourhood.

4. Use of horns should be minimized especially near public places such as hospitals, religious places and
schools.

5. Soundproofing systems should be installed in industries, party halls and other buildings that produce a
high amount of unwanted sounds.

6. Trees should be planted in huge numbers as they can absorb unwanted noise from the environment.

9.Explain the audible and inaudible sounds for

humanbeings and how is inaudible sounds useful
for animals?
Human ear has an audible range of frequencies
ranging between 20Hz to 20000Hz

The inaudible sounds can be divided into two categories as infrasound and ultrasound.
Infrasound Ultrasound
The sounds having a frequency range The sound waves having a frequency range above 20 kilohertz are called
below 20 hertz are called infrasound. ultrasounds.
Having too high frequency, they cannot be heard by human beings as
Infrasound cannot be heard by humans.
well.
Animals like giraffe, rhinoceros and
Bats, dogs and cats use ultrasounds to communicate.
whales use infrasound to communicate.
Ultrasounds can be used for various purposes such as identifying
Infrasound waves are used to treat
abnormalities in the human body or calculating distances under the water
myopia in kids
through SONAR.