The human ear has three main parts - the outer, middle, and inner ear. Sound waves enter the outer ear and cause the eardrum to vibrate. These vibrations are amplified by the three smallest bones in the human body in the middle ear. They transmit the vibrations to the inner ear, where fluid in the cochlea sets up electrical signals in auditory nerves that travel to the brain. The brain then interprets these signals as sound.

3. 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.

4. 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.

6. Characteris
tics of a
sound wave
a sound wave can be described
completely by five characteristics:
wavelength , Amplitude, time-period ,
frequency and velocity.

7. Characteristics
of a sound wave
wavelength Amplitude Time-
Period
Frequency
Velocity
of wave

8. Wavelength
the minimumdistance inwhich a sound wave
repeats itself is calleda wave length.
The SI UNIT for measuring wavelength is metre

9. Amplitude
The 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

10. TIME-PERIOD
Thetime required to produce one complete
waveis called Time-Period of the wave.
OR
The time taken to complete on vibration is
called time-period.

11.  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 vibrationper 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 .

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

13. VELOCITY OF WAVE (OR SPEED OF
WAVE)
The distancetravelledby a wave in one secondis
calledvelocity ofwave ( or speed of wave)
The velocity of wave is representedby the letter v
The SI UNIT for measuring the velocityof a wave
is metres per second(m/s or ms-1 )

14. 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 anobject 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.

15. Production of sound
Soundwaves in air
Propagation of sound ( or Transmission of
sound

16. Sound waves in air
• Sound waves in air consist
of compressions and
rarefactions of air.
• The sound waves in air are
longitudinal waves.

17. Propagation of sound( or transmissionof
sound)
 Whenan object vibrates (and makes sound) , then theair layers
around it also start vibrating in exactly thesame way and carry
sound waves from thesound producing object to our ears.
 In thetransmission of sound throughair ,there is no actual
movementof 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 thenextlayer tillit reaches our ear.

18. The maximum distance moved by avibrating air
layer on either side of it’s originalpositionis
known as the amplitudeof the soundwaves.
The numberof completeback and forth
vibrations of an air layer inonesecondis known
as the frequencyof the soundwave.

19. 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.

20. SOUND CAN TRAVEL THROUGH SOLID ,
LIQUID AND GASES
• Sound travels about 15 times faster in steel thanair.
• The sound of ringing telephonebelltravels through theair in
the room whichis a gas ( or rather a mixtureof gases.)
• Whenthere is no air in something, we say thereis vacuum.

21. SOUND CAN TRAVEL THROUGHVACUUM
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.

22. The case of moon and outer space
 Sound 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.

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

24. 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.

25. Speed of sound in various materials

27. Just likelight , sound canalso be made to change its direction and
bounce back when it falls on ahard surface . the bouncing back of sound
when it strike a hard surface iscalled reflection of sound. Sound is
reflected well from hard surface like wall, a metal sheet, hard wood and
a cliff.

28. Reflectionof sound
 Sound is reflected in the same way aslight . the law of reflection of
light are obeyed during the reflection of sound . we canwrite the
law of reflection of sound as follows:
 The incident sound wave, the reflected sound wave, and the normal
at the point of incidence, alllie in the same plane.
 The angle of reflection of sound is alwaysequal to the angle of
incidence of sound.

29. 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.

30. 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.

31. BULB HORN and MEGAPHONE

32. STETHOSCOPE
Stethoscope 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.

33. STETHOSCOPE

35.  The persistence of sound ina big halldue to repeated reflection from
walls , ceiling and floor of the hallis 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 actuallygood absorber of sound.

36.  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
calledecho‘echocardiography’.
 Ultrasound isused in ‘sonar’ apparatus to measure the depth of sea
and to locate under sea objects like shoal of fish, shipwrecks ,
submarines , searocks and hidden ice berg in the sea.

37.  Therange offrequencyfrom 20Hzto20,000Hzisknownas
frequencyrangeofhumans.
 Thesoundoffrequencieslowerthan20Hzare knownas ‘infrasonic
sounds’
 Earthquakes,andsomeanimalslikewhales,elephantsand
rhinocerosesalsoproduceinfrasonicsounds.
 Thesoundoffrequencyhigherthan20,00Hzare knownas
ultrasonicsound.Wecannothear it
 Achildundertheage of5canhear ultrasonicsoundoffrequency
upto25,000Hz.

39.  The sound having too highfrequencywhich
cannot be heard by human beingsare called
ultrasonic sounds.
 Due to its very highfrequencyultrasound has a
muchgreater penetrating power than ordinary
sound.

41. Ultrasoundwavehaveaveryhighfrequencydueto
whichtheycanpenetrateintomattertoalargeextent.
Ultrasoundisusedinindustriestodetectcracksin
metalsblockswithoutdamagingthem.
Ultrasoundisusedtoinvestigatetheinternalorgansof
thehumanbodysuchaslever,gallbladder, pancreas,
kidneys,uterusandheart,etc.

42. Thetechniqueofobtainingpicture
ofinternalorgansofthebodyby
usingechoesofultrasoundpulsesis
calledultrasonography.
Theuseofultrasoundwavesto
investigatetheactionoftheheartis
calledechocardiography

43. SONAR
The 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

44. 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.

45. LOUDNESS
PITCH
QUALITY

46. 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’.

47.  Pitchis thatcharacteristic of sound by whichwe can
distinguishbetween differentsound of thesame loudness.
 The pitch of the sound depends on the frequencyof 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 isdetermined by thefrequency of
vibration of the object whichproduces sound.

48. QUALITY
 Quality 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.

50. THEHUMANEAR
Constructionof
humanear
Working of
human ear
The
humanear

51. OUTER EAR
MIDDLE EAR
INNER EAR

52. STRUCTURE OF
HUMAN EAR

53. 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.

54. 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.

55. INNEREAR
 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.

56.  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 hammerto 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.