The sensation felt by our ear is called sound.

1.Sound is a form of energy.

2.Sound is that form of energy which makes us hear.

SOUND TRAVELS IN THE FORM OF WAVES

a wave is a vibratory in a

medium which carry

energy from one point to

another without there

being contact between the

two points.

Characteristics of a

sound wavea sound wave can be described

completely by five characteristics:wavelength , Amplitude, time-period ,

frequency and velocity.

Characteristicsof a sound wave

wavelength Amplitude Time-Period

FrequencyVelocity

of wave

Wavelengththe minimum distance in which a sound wave

repeats itself is called a wave length.

The SI UNIT for measuring wavelength is metre

AmplitudeThe maximum

displacement of the particles of the

medium from their original undisturbed

positions, when a wave passes through the

medium, is called Amplitude.

The amplitude of a wave is the same as the

amplitude of the vibrating body producing the

wave

TIME-PERIODThe time required to produce one complete

wave is called Time-Period of the wave.

OR

The time taken to complete on vibration is called time-period.

The term frequency tells us the rate at which the waves are produced by their source . the number of complete waves produced in one second is called frequency of the wave .

The number of vibrations per second is called frequency .

The SI UNIT of Frequency is Hertz . One hertz = one vibration per second . Frequency of the wave is the same as the

frequency of the vibrating body which produces the wave.

The frequency of a wave is the reciprocal of its time period .

FREQUENCY

HEINRICH HERTZ :the scientist after whom the unit of frequency called ‘hertz’ (Hz) is named .

VELOCITY OF WAVE (OR SPEED OF

WAVE)

The distance travelled by a wave in one second is called velocity of wave ( or speed of wave)

The velocity of wave is represented by the letter v

The SI UNIT for measuring the velocity of a wave is metres per second (m/s or ms-1 )

Production of sound• Sound is produced when an object vibrates(moves back and forth rapidly)

• Sound is produced by vibrating objects.

• The energy required to make an object vibrate and produce sound is provided by some outside source (like our hand , wind ,etc)

• The sound of our voice is produced by the vibrations of two vocal cords in our throat.

• In most of the cases , a sound producing object vibrates so fast that we cannot see it’s vibration with our eyes.

Production of sound

Sound waves in air

Propagation of sound ( or Transmission of

sound

Sound waves in air

• Sound waves in air consist of compressions and rarefactions of air.

• The sound waves in air are longitudinal waves.

Propagation of sound ( or transmission of sound)

When an object vibrates (and makes sound) , then the air layers around it also start vibrating in exactly the same way and carry sound waves from the sound producing object to our ears.

In the transmission of sound through air ,there is no actual movement of air from the sound producing body to our ear . the air layer only vibrates back and forth , and transfer the sound energy from one layer to the next layer till it reaches our ear.

The maximum distance moved by a vibrating air layer on either side of it’s original position is known as the amplitude of the sound waves.

The number of complete back and forth vibrations of an air layer in one second is known as the frequency of the sound wave.

Sound need a medium to travel

The substance through which sound travels is

called medium.

Sound needs a material medium like solid ,

liquid , or gas to travel and be heard.

Sound waves are called mechanical waves

because they need a material medium ( like

solid , liquid , or gas) for their propagation.

Though sound wave can not travel through

vacuum but light wave and radio waves can

travel even through vacuum.

SOUND CAN TRAVEL THROUGH SOLID , LIQUID AND GASES

• Sound travels about 15 times faster in steel than air.

• The sound of ringing telephone bell travels through the air in the room which is a gas ( or rather a mixture of gases.)

• When there is no air in something , we say there is vacuum.

SOUND CAN TRAVEL THROUGH VACUUM

Sound cannot travel through vacuum.

Air is necessary for the sound to travel

from the ringing bell to our ears.

Sound can travel through solid, liquid

and gases because the molecules of

solid, liquid and gases carry the sound

waves from one place to another

through their vibrations.

The case of moon and outer spaceSound cannot be herd directly on the

surface of moon because there is no air

on the moon to carry the sound waves

( or sound vibration )

The astronauts who land on moon ( or

walk in outer space ) talk to one

another through wireless sets using

radio waves.

The speed of sound tells us the rate at which sound travel from the sound producing body to our ears

THE SPEED OF SOUND DEPEND ON A NUMBER OF

FACTORS:

The speed of

sound

The speed of

sound depend on

the nature of

materials ( or

medium )which it

travel

The speed of

sound depends

on the

temperature.

The speed of

sound depend

on the

humidity of

the air.

Speed of sound in various materials

Just like light , sound can also be made to change its direction and bounce back when it falls on a hard surface . the bouncing back of sound

when it strike a hard surface is called reflection of sound. Sound is reflected well from hard surface like wall , a metal sheet, hard wood and

a cliff.

Reflection of sound Sound is reflected in the same way as light . the law of reflection of

light are obeyed during the reflection of sound . we can write the law of reflection of sound as follows:

The incident sound wave, the reflected sound wave, and the normal at the point of incidence, all lie in the same plane.

The angle of reflection of sound is always equal to the angle of incidence of sound.

Application of reflection of sound

• The reflection of sound is utilised in

the working of devices such as

:megaphone, bulb horn ,stethoscope

,and soundboard. All these device

involve multiple reflection of sound waves.

Megaphone and bulb horn

The devices like megaphone and bulb horn are all designed to send sound in particular direction ,without spreading all around .

A megaphone works on the multiple refraction of sound.

A bulb horn is a cone-shaped wind instrument which s used for signalling in bicycles , cars , buses , trucks ,and boats , etc.

A bulb horn also works on multiple refraction of sound.

BULB HORN and MEGAPHONE

STETHOSCOPEStethoscope is a medical instrument

used by the doctors for listening t the sound produced within the humans body , mainly in the heart and lungs.

The stethoscope works on the principle of multiple reflection of sound.

STETHOSCOPE

The persistence of sound in a big hall due to repeated reflection from walls , ceiling and floor of the hall is called reverberation.

If the reverberation is too long , then the sound becomes blurred , distorted and confusing due to overlapping of different sounds.

Te soft and porous material are bad reflector of sound. The soft and porous materials are actually good absorber of sound.

The technique of obtaining pictures of internal organs of the body by using echoes of ultrasound pulses is called ultrasonography.

The use of ultrasound waves to investigate the action of the heart is called echo ‘echocardiography’.

Ultrasound is used in ‘sonar’ apparatus to measure the depth of sea and to locate under sea objects like shoal of fish, shipwrecks , submarines , sea rocks and hidden ice berg in the sea.

The range of frequency from 20Hz to 20,000 Hz is known as frequency range of humans.

The sound of frequencies lower than 20Hz are known as ‘infrasonic sounds’

Earthquakes, and some animals like whales, elephants and rhinoceroses also produce infrasonic sounds.

The sound of frequency higher than 20,00Hz are known as ultrasonic sound. We cannot hear it

A child under the age of 5 can hear ultrasonic sound of frequency up to 25,000Hz.

The sound having too high frequency which cannot be heard by human beings are called ultrasonic sounds.

Due to its very high frequency ultrasound has a much greater penetrating power than ordinary sound.

Ultrasound wave have a very high frequency due to which they can penetrate into matter to a large extent.

Ultrasound is used in industries to detect cracks in metals blocks without damaging them.

Ultrasound is used to investigate the internal organs of the human body such as lever , gall bladder, pancreas , kidneys , uterus and heart, etc.

The technique of obtaining picture of internal organs of the body by using echoes of ultrasound pulses is called ultrasonography .

The use of ultrasound waves to investigate the action of the heart is called echocardiography

SONARThe word SONAR stands for ‘SOund Navgation And Ranging’. sonar is an apparatus or

device which is used to find the depth of a sea or to locate the under-water things like shoals and fish , shipwrecks , and enemy submarines.

The time it takes for n echo to return is used to find out how far away something is.

Sonar apparatus consist of two parts:

I ]a transmitter

ii]a receiver

The sonar device measures the time taken by the ultrasonic sound pulse to travel from the ship to the bottom of the sea , and back to the ship.

Speed of ultrasound is same in water as that of ordinary sound.

Bats use ultrasonic sound to fly in night. Bats search their prey at night by the method of echolocation.

LOUDNESS

PITCH

QUALITY

LOUDNESS

The loudness of sound is a measure of the sound energy reaching the per second.

The loudness of sound depends on the amplitude of sound waves.

Greater the amplitude of sound waves louder the sound will be.

The loudness of sound is measured in ‘decibel’ written as ‘dB’.

Pitch is that characteristic of sound by which we can

distinguish between different sound of the same loudness.

The pitch of the sound depends on the frequency of vibration. The pitch of a sound is directly proportional to its frequency.

Faster the vibration of the sound producing source , the higher is the frequency and higher is the pitch.

The pitch of the sound is determined by the frequency of vibration of the object which produces sound.

QUALITYQuality is that characteristic of musical

sound which enables us to distinguish between the sound of same pitch and loudness produced by different musical instruments.

The quality of a musical sound depends on the mixture of frequencies present in it.

THE HUMAN EAR

Construction of

human ear

Working of

human ear

The

human ear

OUTER EAR

MIDDLE EAR

INNER EAR

STRUCTURE OF HUMAN EAR

OUTER EAR

The part of ear which we see outside the head is called our outer ear.

The outer ear consist of a broad part called pinna and about 2 to 3 centimetre long passage called ear canal . at the end of ear canal is a thin , elastic , and circular membrane called tympanum[ear drum].

The outer ear contains air.

MIDDLE EAR

The middle ear contains three small and delicate bones called hammer ,anvil and stirrup.

These are linked to one another .one end of the bone called hammer is touching the ear drum and its other end is connected to second bone called anvil . the other end of anvil is connected to the third one called stirrup.

The lower part of middle ear has a narrow tube called ‘Eustachian tube’ going to the throat.

INNER EAR

The inner ear has a coiled tube called cochlea. One side of cochlea is connected to the middle ear through the elastic membrane over the oval window.

The cochlea is filled with a liquid.

The liquid present in cochlea contains nerve cells which are sensitive to sound.

The outer side of cochlea is connected to the auditory nerve which goes into brain.

When the sound waves fall on the ear drum , the ear drum starts vibrating back and forth rapidly.

The vibrating ear-drum causes a small bone hammer to vibrate. The vibrating stirrup strikes on the second bone anvil and finally to the third bone stirrup . the vibrating stirrup strikes on the membrane of the oval window and passes its vibration to the liquid cochlea sets up electrical impulses in the nerve cells present in it. These electrical impulses are carried by auditory nerve to the brain. The brain interprets these electrical impulses as sound and we get the sensation of hearing.

Thus the function of three tiny bones in the middle ear is to increase the strength of vibration coming from the ear drum before passing them on to the inner ear.