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SOUND

Definition: - Vibrations transmitted through an solid or a liquid or gas, with frequencies in the approximate range of

20 to 20,000 hertz, capable of being detected by human organs of hearing.

OR

Is a form of energy, that gives the sensation of hearing.

Basic concepts concerning about sound

1. Cause of generation of sound

2. Reasons for different sound from different sources.

3. Propagation of sound from one place to other place.

4. Mechanism of hearing of sound by human ear.

Sounds and Vibrations

Rapid Back and forth movement of molecules of matter is called

vibrations.

Sound is produced because of vibrations.

If the vibrations are very small,

it may not be possible to detect

the sound. Vibrations are easily

seen to be produced by the

following instruments:-

Sound produced by Humans

In the human body Voice

box or larynx help us to

produce sound.

The voice box has two

vocal chords stretched

across it. These vocal

chords help the air to pass

through it.

The lungs force air

through the narrow gap

present between the two

vocal chords and makethem vibrate to produce

sound.

The muscles attached to

the vocal chords can make

them tighter or loosened

/thinner or thicker. These

changes in the vocal

chords help to change the

pitch of the sound.

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Sound Produced By animals

Different types of birds and animals have different mechanism in their bodies for producing their characteristics

sounds.

1. Most of the animals use their vocal chords to produce sound as the human beings produces the sound by using

vocal chords. e.g.-Dog-Bark/Cats-Mew/Horse-Neigh/Lions-Roar and Cows -Moo.

2. Birds have a ring of cartilage called SYRINX in their voice box to produce their characteristics sound.

3. Insects use their wings to produce sound. They vibrate their wings rapidly so that they can produce SOUND.

More is the vibration higher will be the pitch of the sound.

4. Frogs use their vocal sacs to produce sound. The BULGING of their throat helps them to make their croaking

louder.

PROPAGATION OF SOUND

Sound needs a medium for its propagation. It cannot propagate through vacuum but it can propagate through all

the three states of matter i.e. solid liquid and

Ex- When a person speaks, the air closer to his mouth is

pushed in the direction of sound. The air molecules get distributed

and start vibrating about their mean position. Such molecules

which vibrate will disturb the nearest molecules for vibrating

them. Continue this method until the molecules starts vibration

which is nearer to listener. This causes the vibrations in the

diaphragm of the ear.

The sound is always produced by vibrating body. When

gong of a bell is struck with a hammer, sound i

produced. The gong is set into the vibrations and sound

waves are propagated in the air. When these waves reach

the ear, the ear drum is set into vibrations. Thes

vibrations are communicated to brain and we ge

sensation through the hearing.

Experiment to show that sound require a material medium for its propagation

Aim :To show that sound can travel through air but cannot travel

through vacuum

Material required: An electric bell , a big glass jar, a vacuum pump.

Method: Hang the bell inside the glass jar connected to the vacuum

pump. When the bell is switched on, the sound is heard. Now, switch

on the vacuum pump. We will observe that as the air is pumped out, the

sound becomes faint and finally disappears.

Result: sound cannot travel through vacuum.

FACTORS ON WHICH THE SPEED OF SOUND DEPENDS

TEMPERATURE

NATURE OF MEDIUM

WIND VELOCITY

MEDIUM AIR(DRY) WATER STEEL

SPEED OF SOUNDAT 0O 330m/s 1500m/s 6000m/s

SOLID (FASTEST) > LIQUIDS >

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Light propagates faster than sound

The following examples show that sound takes an appreciable time to travel from one place to another then light..

Though lightning and thunder are produced simultaneously, the flash of the lightning is seen much before

the sound of the thunder.

When a gun is fired at some distance, the flash is seen before the sound is heard.

The steam coming out from the whistle of an engine is seen before the sound is heard.

In a cricket match, the striking of the ball by the batsman is seen before hearing the sound.

Reason: The speed of sound is 330m/s in air where as the speed of light is 3 x 108 m/s , which is much

faster than the speed of sound. Hence light reaches earlier than the sound.

Test yourself

Q What is the other name of the vocal cordsQ Why cant two astronauts hear each other on the surface of the moon?

Q During a thunder storm, the sound of thunder is heard after lightning is seen. Give reason.

Q Explain in brief, how is sound produced?

Q You can easily hear the sound of an approaching train by putting your ear on the railway track well before the sound

is heard in the air. Why?

Q With the help of a diagram, Explain that sound cannot propagate through vacuum

OR

With the help of a diagram show that sound needs a material medium for propagation

Audible and Inaudible sound:-

The sound which can be heard by a human being is called audible sound.

RANGE OF AUDIBLE SOUND: 20 Hz to 20,000 Hz .

Sound frequency Type of sound

Below 20 Hz Infrasonic sound(Inaudible

sound)

Between 20 Hz to 20,000 Hz Audible sound( SONIC

SOUND)

Above 20,000 Hz Ultrasonic sound(Inaudible

sound)

TEST FOR YOURSELF

Q Name the sound having frequency a) less than 20Hz b) between 20 and 20000Hz c) Greater than 20,000Hz

Q To which frequency range is the human ear sensitive?

Q Name two animals, birds that can hear ultrasonic sounds.

Ultrasonic sound are produced by dolphins

bats and porpoises.

Infrasonic sound are produced by whales an

elephants and they can observe the

earthquake before the main shock waves.

Bat is able to locate any obstacle i

its path due to the reflection of the

ultrasonic waves from the object.

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Persistence of Hearing:-

The impression of sound heard by our ears persists in our mind for 1/10th of a second.

Sound takes only 1/10th of a second to reach our ear when the sound producing body is 33 meter away from the

ear.

Sound is always reflected back when it fall on the objects around them, these reflected sound reach to our ear

in the time less than 1/10th of a second.

If the reflected sound and the direct sound reach to our ear in mingled form then it is slightly difficult to

distinguish between them.

Reflected sound can only be hear when the reflecting surface is 17 meter away from the ear.

Structure of the EarThe outer ear:

The outer ear consists of the pinna.

Pinna collects the sound vibrations from the air.

These sound vibrations reach to the ear drum through ear canal/auditory canal.

Middle ear:

It is air filled cavities which lies just beyond the ear drum and is surrounded by a bone.

There are three bones in the cavity. The hammer (malleus), anvil (incus) & stirrup(stapes).

These small bones help to amplify the vibrations.

Inner ear:

The inner ear is embedded in the bone of the skull and is filled with a liquid.

Consists of main organ of hearing called COCHLEA, that carries the vibrations in the form pf electrical

impulses from the AUDITORY NERVE to the BRAIN

1. The sound makes the

ear drum vibrate.

3. The bones make the

fluid and hair move

4. The auditory nerve takes

the message to the brain

2The ear drum carries

the vibrations to the

three bones

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W orking of the Ear

Sound waves enter the external ear and

strike on the eardrum causing it to vibrate. These vibrations are amplified many times

by three bones: (i) hammer (ii) anvil (iii)stirrup, in the middle ear and transmitted to

the inner ear by the hollow bones of the middle ear.

The inner ear has coiled tube called cochlea.

The tiny hairs present in it picks up the vibrations and sends the signals to the brain through auditory nerve tothe brain, which interprets and make us hear sounds.

TEST YOURSELF

Q Name the three bones present in ear

Q Name the main organ of hearing

Q Name the nerve that connects the ear to the brain

Q what is the function of the three bones present in the ear.

Q Draw a neat labeled diagram of human ear, explaining how the energy of the sound wave is transmitted to the nerves

in the cochlea

Echoes:-

The sound heard after reflection from a rigid obstacle is called an

echo.

The minimum distance to hear an echo is 17m.

Echo is generally observed in the open field, in empty buildings

etc.

Advantages

Used in SONAR (sound navigation and ranging) to find the

depth of the sea.

Bats locate prey by returning echoes.

Dolphins also use the returning echoes to locate its prey. This

is called ECHOLOCATION

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AMPLITUDEThe maximum displacement from the central position of

vibrating body is called amplitude.

SI unit of amplitude is METER.

Frequency:-

The number of cycles completed by a vibrating body in one second is called frequency.

FREQUENCY is measured in number of cycle per second.

Therefore the SI unit of frequency is HERTZ.

Frequency = Number of cycle completed / second.

TIME PERIOD:

The time taken to complete one vibration is called timeperiod

SI unit of time period: seconds

PITCH:

The shrillness of a sound is called pitch.

Pitch depends upon the FREQUENCY

IF FREQUENCY IS HIGH, PITCH IS HIGH(SHRILLSOUND, as in females); IF FREQUENCY IS LOW, PITCH IS

LOW( FLAT OR GRAVE SOUND, as in males)

Pitch frequency

LOUDNESS OF A SOUND: Loudness means how much energy does the sound possess

Depends upon the amplitude . more the amplitude more is

the loudness and farther the sound will travel.

UNIT OF LOUDNESS: DECIBEL

Threshold of hearing:-

The faint sound which a human ear can detect is called threshold of

hearing. The threshold of hearing is similar to zero decibel.

Unpleasant and Pleasant sound:-

NOISE MUSIC

Produced by irregular or non periodic vibrations Produced by periodic or regular vibrations

unpleasant to hear Pleasant to hear

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TEST YOURSELF

Q On what factors does the loudness of a sound depends

Q In which unit is the loudness of sound depends

Q which sound has a higher pitch? A) low frequency B) high Frequency

Q What kind of sound is produced by musical instruments?

Q Define the terms a) Frequency b) amplitude c) time period. Also give their SI units

NOISE A HEALTH HAZARD

LOUD AND HASRH SOUND IS CALLED NOISE.

Noise is produced by irregular vibrations

THE DISTURBANCE CAUSED BY AN UNDESIRABLE LOUD SOUND OF DIFFERENT KINDS IS CALLED

NOISE POLLUTION.

EFFECTS OF NOISE POLLUTION:

Hearing loss

Fatigue

High blood pressure

Extreme emotional behaviour

WAYS TO REDUCE NOISE LEVEL

Setting up industries away from residential areas

Planting more trees as they absorb sound

Restricted use of loudspeakers and auto horns

Use of carpets , curtains at homes

Q What is noise and noise pollution ? How does noise pollution affect us? How can noise pollution be reduced