2. When a particleWhen a particle
moves to and fromoves to and fro
about its meanabout its mean
position , it is saidposition , it is said
to vibrate.to vibrate.
This to and froThis to and fro
motion is called amotion is called a
vibration.vibration.
Every source ofEvery source of
sound is a vibratingsound is a vibrating
body.body.
3. A tuning fork is a U – shapedA tuning fork is a U – shaped
steel fork provided with a steelsteel fork provided with a steel
handle.handle.
Prongs
Stem
The two arms of the U areThe two arms of the U are
called prongs , whereas thecalled prongs , whereas the
handle is called stem .handle is called stem .
It is a convenient source ofIt is a convenient source of
producing sound vibrationsproducing sound vibrations
in a laboratory.in a laboratory.
4. Take a small thermocol ball andTake a small thermocol ball and
suspend it from an iron stand with asuspend it from an iron stand with a
light silk thread.light silk thread.
Strike one of the prongs of the tuningStrike one of the prongs of the tuning
fork on the hard rubber pad and bringfork on the hard rubber pad and bring
it close to your ear and you will beit close to your ear and you will be
able to hear the sharp hummingable to hear the sharp humming
sound of the tuning fork.sound of the tuning fork.
Now touch one prong of the tuningNow touch one prong of the tuning
fork to the thermocol ball .fork to the thermocol ball .
You will observe that thermocol ballYou will observe that thermocol ball
flies outward.flies outward.
Thus, the experiment proves that theThus, the experiment proves that the
sound produced by a tuning fork issound produced by a tuning fork is
due to the vibration of its prongs .due to the vibration of its prongs .
5. OscillatoryOscillatory
motion –motion – This toThis to
and fro motion ofand fro motion of
the pendulumthe pendulum
about its meanabout its mean
position is calledposition is called
one vibration. Thisone vibration. This
is also calledis also called
oscillatoryoscillatory
motion .motion .Eg-Eg-AA
simple pendulumsimple pendulum..
6. Amplitude –Amplitude – The maximumThe maximum
displacement of a vibrating bodydisplacement of a vibrating body
from its mean position is called itsfrom its mean position is called its
amplitude.amplitude.
It has been found that larger theIt has been found that larger the
amplitude , more is the loudness.amplitude , more is the loudness.
Eg –Eg – If a drum hit softly ,a softIf a drum hit softly ,a soft
sound is produced, because thesound is produced, because the
amplitude is less . If the sameamplitude is less . If the same
drum is hit hard , a loud sound isdrum is hit hard , a loud sound is
produced as the amplitude is veryproduced as the amplitude is very
large.large.
SI unit of amplitude is metreSI unit of amplitude is metre
7. Frequency –Frequency – The number of vibrations produced by a vibratingThe number of vibrations produced by a vibrating
body in one second is called frequency. It is denoted by letterbody in one second is called frequency. It is denoted by letter f .f .
The frequency of vibrations determines the shrillness or the pitchThe frequency of vibrations determines the shrillness or the pitch
of any sound. If the frequency of vibration is low , we say the soundof any sound. If the frequency of vibration is low , we say the sound
has low pitch or is bass. Conversely , if the frequency of vibration ishas low pitch or is bass. Conversely , if the frequency of vibration is
high , we say that the sound has high pitch or is shrill.high , we say that the sound has high pitch or is shrill.
Eg – The voice of a child is shriller than that of an adult .Eg – The voice of a child is shriller than that of an adult .
8. The unit of frequency in SIThe unit of frequency in SI
system issystem is Hertz .Hertz . When aWhen a
vibrating body produce onevibrating body produce one
vibration in one second , thenvibration in one second , then
its frequency is said to beits frequency is said to be oneone
Hertz .Hertz .
If the frequency of a tuningIf the frequency of a tuning
fork is 256 Hz, it means it isfork is 256 Hz, it means it is
producing 256 vibrations inproducing 256 vibrations in
one second.one second.
9. The time a vibrating body takesThe time a vibrating body takes
to complete one vibration isto complete one vibration is
called itscalled its time period.time period.
It is denoted by letter ‘It is denoted by letter ‘t’t’..
If ‘f’ is the frequency of vibratingIf ‘f’ is the frequency of vibrating
body and ‘t’ is the time periodbody and ‘t’ is the time period
then:then:
‘‘f’ vibrations are completed inf’ vibrations are completed in
1s1s
:one vibration is completed in =:one vibration is completed in =
1/f *s1/f *s
T=1/f i.e., Time period =T=1/f i.e., Time period =
10. If the frequency of theIf the frequency of the
vibrations is less than 20 Hz,vibrations is less than 20 Hz,
then human ears cannot hearthen human ears cannot hear
it. Such vibrations are calledit. Such vibrations are called
infrasonic vibrations.infrasonic vibrations.
If the frequency of vibration isIf the frequency of vibration is
between 20 Hz TO 20,00 Hz,between 20 Hz TO 20,00 Hz,
then they can be perceived bythen they can be perceived by
the human ear . Such vibrationsthe human ear . Such vibrations
are calledare called sonic vibrations.sonic vibrations.
However, if the frequency ofHowever, if the frequency of
vibrations is above 20,000 Hzvibrations is above 20,000 Hz
then human ear cannotthen human ear cannot
perceive them . Such vibrationsperceive them . Such vibrations
are calledare called ultrasonic soundsultrasonic sounds ..
11. Dogs can hear upto theDogs can hear upto the
frequency of 40,000Hz. Dogsfrequency of 40,000Hz. Dogs
can respond to a whistle whichcan respond to a whistle which
produce ultrasonic vibrationsproduce ultrasonic vibrations
and is calledand is called Galton whistleGalton whistle..
Bats produce vibrations in theBats produce vibrations in the
frequency range of 50 Hz tofrequency range of 50 Hz to
80,000Hz. Bats have very80,000Hz. Bats have very
weak eyes . When bats fly inweak eyes . When bats fly in
the night, they producethe night, they produce
ultrasonic vibration . Whenultrasonic vibration . When
these vibrations strike thethese vibrations strike the
insect, they are reflectedinsect, they are reflected
back .on receiving the reflectedback .on receiving the reflected
sound, the bat can locate thesound, the bat can locate the
insect.insect.
Dolphins also use ultrasonicDolphins also use ultrasonic
sounds to locate their preysounds to locate their prey..
12. UltrasonicUltrasonic
vibrations arevibrations are
used for imagingused for imaging
internal organs ofinternal organs of
human body.human body.
UltrasonicUltrasonic
vibrators arevibrators are
used to driveused to drive
rat andrat and
cockroachescockroaches
from godown.from godown.
These vibrations are used inThese vibrations are used in
relieving pain in joints andrelieving pain in joints and
muscles.muscles.
These vibrations are used inThese vibrations are used in
detecting flaws in articlesdetecting flaws in articles
made from metals. Etcmade from metals. Etc..
13. The speed of sound in steel is around 5100 m/s.The speed of sound in steel is around 5100 m/s.
By knowing the speed of sound in water , we can find theBy knowing the speed of sound in water , we can find the
depth of the sea .depth of the sea .
The speed of sound in water is around 1600 m/s.The speed of sound in water is around 1600 m/s.
Sound energy travels fastest in solidsSound energy travels fastest in solids
Sound is slower in liquidsSound is slower in liquids
It is slowest in gases . In air ,the speed is around 330 m/s.It is slowest in gases . In air ,the speed is around 330 m/s.
14. We have learnt that sound travels throughWe have learnt that sound travels through
solids, liquids and gases . But sound cannotsolids, liquids and gases . But sound cannot
travel through vacuum.travel through vacuum.
A material medium is necessary for theA material medium is necessary for the
propagation of sound.propagation of sound.
15. Shining objects like mirror , metal or hard objects like buildingShining objects like mirror , metal or hard objects like building
or stone reflect sound. However, materials with loose textureor stone reflect sound. However, materials with loose texture
absorb sound. Eg-absorb sound. Eg- curtains, gunny bag ,straw, carpets,curtains, gunny bag ,straw, carpets,
e.t.c. absorb sound.e.t.c. absorb sound.
Auditoriums are carpeted and their walls are coated with someAuditoriums are carpeted and their walls are coated with some
rough materials, so that they do not reflect any sound.rough materials, so that they do not reflect any sound.
16. Different objects produce differentDifferent objects produce different
sounds because either they havesounds because either they have
different loudness or differentdifferent loudness or different
pitches or both. Eg- The sound ofpitches or both. Eg- The sound of
a girl is more shrill as compared toa girl is more shrill as compared to
the sound of a boy.the sound of a boy.
Loudness –Loudness – Loudness is theLoudness is the
characteristic of a sound whichcharacteristic of a sound which
distinguishes a feeble sound fromdistinguishes a feeble sound from
a loud sound of the samea loud sound of the same
frequency.frequency.
The loudness of sound dependsThe loudness of sound depends
upon the amplitude of the vibratingupon the amplitude of the vibrating
body.body.
17. Pitch-Pitch- The voice of a woman is more shrill than theThe voice of a woman is more shrill than the
voice of a man . A shrill sound is calledvoice of a man . A shrill sound is called high pitchhigh pitch
sound,sound, whereas a soft or shrill sound is calledwhereas a soft or shrill sound is called lowlow
pitch sound.pitch sound. Pitch is the effect produced in the earPitch is the effect produced in the ear
due to the sound of some particular frequency. Pitchdue to the sound of some particular frequency. Pitch
depends upon the frequency of a vibrating body, i.e.,depends upon the frequency of a vibrating body, i.e.,
higher the pitch , the more is the frequency and thehigher the pitch , the more is the frequency and the
lower the pitch, the less is the frequency.lower the pitch, the less is the frequency.
18. Noise- A sound does notNoise- A sound does not
have a pleasing sensationhave a pleasing sensation
on the ears is calledon the ears is called noise.noise.
Scientifically, a noise is producedScientifically, a noise is produced
by irregular vibrations. Eg- soundby irregular vibrations. Eg- sound
of too many people talking at oneof too many people talking at one
time, bark of a dog.time, bark of a dog.
Music – A sound which has aMusic – A sound which has a
pleasing sensation on the ears ispleasing sensation on the ears is
calledcalled musicmusic. Scientifically , a. Scientifically , a
musical vibration is produced bymusical vibration is produced by
regular vibrations. Eg- the prongregular vibrations. Eg- the prong
of the tuning fork of a sitarof the tuning fork of a sitar
vibrates at regular intervals andvibrates at regular intervals and
is called music .is called music .
19. The loudness of sound is measured in decibelsThe loudness of sound is measured in decibels
(dB). It signifies the sound pressure level.(dB). It signifies the sound pressure level.
Human ears can pick up sound from 10 dB toHuman ears can pick up sound from 10 dB to
180 dB . A human being can tolerate loudness180 dB . A human being can tolerate loudness
of 80 dB . The sound above 80 dB is painful andof 80 dB . The sound above 80 dB is painful and
causes various health problems.causes various health problems.
20. The disturbance produced in the environment byThe disturbance produced in the environment by
undesirable , loud and harsh sound from variousundesirable , loud and harsh sound from various
sources is called noise pollution.sources is called noise pollution.
The noise pollution at a particular place isThe noise pollution at a particular place is
determined by the following factors:determined by the following factors:
(I) Loudness of the sound.(I) Loudness of the sound.
(2) Duration of noise.(2) Duration of noise.
21. Noise in homes - 1.Noise in homes - 1. televisiontelevision , 2., 2.
power musicpower music systemsystem, 3., 3.desert coolerdesert cooler,,
4.4. vacuum cleanervacuum cleaner, 5., 5. typetype writer.writer.
Noise in surroundings – 1.Noise in surroundings – 1. loudloud
speakers atspeakers at marriagesmarriages , 2., 2.explodingexploding
crackerscrackers, 3., 3. hawkershawkers,4.,4. publicitypublicity
announcementsannouncements..
Noise in factories –Noise in factories – All factories bigAll factories big
or small use machines , whichor small use machines , which
invariably produce noise.invariably produce noise.
Noise due to transportation –Noise due to transportation – 1.1.
train , 2 . All kinds of petrol and dieseltrain , 2 . All kinds of petrol and diesel
vehicles , 3 . Aeroplanesvehicles , 3 . Aeroplanes
22. Noise in surroundings interferes inNoise in surroundings interferes in
conversation with another person.conversation with another person.
A long exposure to noise may resultA long exposure to noise may result
in loss of hearing.in loss of hearing.
It causes anger , tension ,It causes anger , tension ,
headaches , irritability and nervousheadaches , irritability and nervous
tension.tension.
It can cause loss of night vision asIt can cause loss of night vision as
well as colour blindness. ,e.t.c.well as colour blindness. ,e.t.c.
23. Factories should be relocated far away from residentialFactories should be relocated far away from residential
areas .areas .
Use of loudspeakers for various social or religiousUse of loudspeakers for various social or religious
events should be banned .events should be banned .
At homes ,T.V., radio , e.t.c. should be played at lowAt homes ,T.V., radio , e.t.c. should be played at low
volume.volume.
Heavy vehicles should not be allowed in residentialHeavy vehicles should not be allowed in residential
areas.areas.
