A perfect ppt for your class 9 project on Sound which includes all topics and subtopics as covered in NCERT.

1. TOPIC-SOUND
NAME-KRITIKA
CLASS- IX B
ROLL NO.- 23
SUBJECT- SCIENCE
Not we make sound but, sound
does makes us...

2. WhatisSound?
– Soundis a formofenergy which producesa sensationof hearingin ourears.OrSoundis amechanical
wavethatis anoscillationof pressuretransmittedthrougha solid,liquid, orgas, composedof frequencies
withinthe rangeof hearingandofa level sufficientlystrongtobe heard,orthe sensationstimulatedin
organsofhearing bysuchvibrations.

3. Production of Sound..
– A sound is produced because of a vibration. A Vibration can be defined
as a rapid back and forth movement of a body about a central position.
Thus, sound is a capable of being heard. The organ in human beings that
is involved in the production of sound is the larynx. The voice is situated
in the neck at the upper end of the wind pipe. The sound produced is
controlled by vocal cords, which are thin membranes stretched across the
voice box. There are muscles attached to the vocal cords. These muscles
are vary the tension in the vocal cords. With the help of these muscles,
we can make different sounds.

4. PropagationofSound
– Sound is produced by vibrating objects in a medium through which it is
transmitted. It can either be solid, liquid or gas. When an object vibrates,
medium to vibrate fro their mean position. The first particle vibrates then
so on results in hearing of sound. After the displacement the particles
– A wave is a disturbance that moves through a medium when the particles
of medium set neighboring particles into motion. Sound Waves are called
travel in air but it cannot travel in vacuum.
SOUND WAVE

5. Soundwavestravelintwoforms..
Longitudinal waves ..
– In a longitudinal wave,the motion of themedium is
parallelto the directionof thewave. This meansthat the
particlesmove left and right whichin turn makesthe other
particlesstart to oscillate. Sound wavesarelongitudinal
waves.It has Compressionsand rarefactions.
– Another exampleof a longitudinal waveis a P waveor
primary waveduring an earthquake.P wavesarealso
knownas compressionalwaves,becauseof the pushing
and pulling they do..
Transverse waves..
– Atransverse waveis awave in which the motion ofthe
medium is a rightangles to the direction ofthe wave.. A
wave on arope is a transverse wave. Light andother
electromagnetic waves arealso transverse waves.
– Another type of transverse wave is the S waveor
secondary wave,which is the second waveyou feel in an
earthquake.

6. Characteristics of sound..
Frequency –
It tells us the number of oscillations perunit time. Thechange in density from the maximum
value to theminimum value, again to maximum valuemakes a complete oscillation. If we
can count the number of compressions and rarefactions perunit time then we can calculate
the frequency of sound wave.
Frequency is usually represented by or nu. Its SI unit is hertz(Hz)named after Heinrich
Rudolph Hertz. How the brain interprets the frequency ofan emitted sound is called its
pitch.

7. II. Amplitudeofsoundwave
Theamplitudeofsoundwaveis theheight of thecrestortough.It is represented bytheletterA.TheSI unitis
the sameas thatofdensityorpressure.Theloudnessorsoftnessofasoundis determined basicallybyits
amplitude.Theamplitudeofthesoundwavedepends uponthe forcewith whichanobjectismadetovibrate.
If westrikeatable lightly,we hearasoftsoundbecauseweproducea soundwaveofless energy (amplitude).If
wehit thetablehardweheara loudsound.
AMPLITUDE
LOUDSOUND
SOFT SOUND

8. III.. Speed of Sound
The speed ofsoundis definedasthedistancewhich apointon awave,such asacompressionor ararefaction,
travelsperunittime.
Weknowthat, speed=wavelength ×frequency
Orv = λν
The speed ofsoundis morein solids,less in liquids andleastin gases.The speed ofsoundalsodepends onthe
temperatureofthe medium. If thetemperatureofthe medium is more, thespeed ofsoundismore.

9. Some important terms…
– The distancebetween twoconsecutivecompressions(C) ortwoconsecutive rarefactions(R)is called the
wavelengthrepresentedbylambda( λ).
– The time takenbytwoconsecutive compressionsorrarefactionstocross afixedpointis called thetime
periodofthewaveOrthetimetakenforonecompleteoscillation.Itis representedbythe symbolT.Its SI
unitis second (s).
Relation between frequency and time period....
v=
1
𝑇
or T=
1
𝑣
Where,Tand v are directly proportional.
λ
Representation of λ

10. Loudness Intensity
Intensity is the rate at which is
transferred across a given units
Loudness is related to
the amplitude of sound waves.

11. SONICBOOM
A sonic boom isa loudsoundkindoflike anexplosion.It's caused byshockwavescreatedby any
objectthattravelsthroughtheairfasterthanthespeedofsound. Sonicbooms createhugeamountsof
soundenergy.Whenan objectmovesthroughtheair,itmakespressurewavesin frontofandbehindit.
A sonicboomhasthecapacitytoshatterglassesandwindowpanes.

12. Reflectionof Sound
– Sound gets reflected at the surface of a solid or liquid and follows the laws of reflection.
i) The angle of incidence is equal to the angle of reflection
ii) The incident ray, the reflected ray and normal at the point of incidence all lie in the same plane.

13. Echo
– If we shout or clap near a reflecting surface like tall building or a
mountain, we hear the same sound again. This sound which we hear is
called echo. It is caused due to the reflection of sound. To hear an
echo clearly, the time interval between the original sound and the
echo must be at least 0.1 s. Since the speed of sound in air is 344
m/s, the distance travelled by sound in 0.I s = 344 m/s x 0.1 s = 34.4
m So to hear an echo clearly, the minimum distance of the reflecting
surface should be half this distance that is 17.2 m.
– Reverberation
Echoes may be heard more than once due to repeated or multiple
reflections of sound from several reflecting surfaces. This causes
persistence of sound called reverberation. In big halls or auditoriums to
reduce reverberation, the roofs and walls are covered by sound

14. Uses of MultipleReflectionof Sound
– 1) Megaphones or loudhailers, horns, musical instruments are all designed to send sound in a particular
direction without spreading it in all directions. In these instruments, a tube followed by a conical opening
reflects sounds successively to guide most of the sound waves from the source in the forward direction.
2) In stethoscope the sound of a patient's heartbeat is guided by along the tube of the stethoscope to the
doctor's ears by multiple reflections of sound.
3) The ceilings of a concert halls, conference halls and cinema halls are made curved so that sound after
reflection reaches all the corners of the halls.
4) Sound boards in large halls or auditorium, large concave wooden boards are placed behind the speaker.
The speaker stands at the focus of this concave reflecting surface. After reflection the sound is spread
evenly towards the audience. This makes the sound readily available even at a distance.

15. Range of Hearing....
– Human beings can hear sound
frequencies between 20 Hz
and 2000 Hz. Sound whose
frequency is less than 20 Hz
is called infrasonic sound.
Sound whose frequency is
more than 2000 Hz is called
ultrasonic sound.

16. Ultrasound andApplications
– Ultrasounds are high frequency waves. Ultrasounds are able to travel
along well defined paths even in the presence of obstacles. Ultrasounds
are used extensively in industries and for medical purposes.
i. Ultrasound is generallyused to cleanparts located inhard-to-reachplaces,for example,spiraltube, odd shapedparts,
electroniccomponentsetc.
ii. Ultrasounds can beused to detectcracksand flawsinmetalblocks. Metalliccomponentsare generallyused in
construction of big structures likebuildings, bridges, machinesand also scientificequipment.
iii. Ultrasonic wavesare madeto reflectfrom various partsof theheartand form the imageof the heart.This technique is
called ‘echocardiography’.
iv. Ultrasound scanner isan instrumentwhichuses ultrasonic wavesfor gettingimages of internalorgans of the human
body. A doctor may imagethe patient’s organs such as theliver,gall bladder, uterus,kidney, etc.It helps the doctor to
detectabnormalities,such as stones in the gall bladder and kidneyor tumorsindifferentorgans.

17. SONAR
– SONAR (originallyanacronym for SOund Navigation And Ranging)is atechniquethatuses soundpropagation
(usuallyunderwater,as in submarinenavigation)to navigate,communicate withor detect objects on or under
thesurfaceof thewater,suchas other vessels.
In thismethod, to find thedepth of anocean,a strongultrasonicwaveis sentfrom theship towards thebottom
of theocean. This ultrasonicwaveis received backafter itis reflected from the bottom of thesea.The time
intervaltfor travelof sound wavesfrom thesource to thereceiver after reflection isnoted. Thedistancetravelled
by theultrasoundrayis given by the equation: 2d X vt,wherev is thevelocity of sound. From thisthedepth d
canbe calculated.

18. HUMAN EAR…
Thehumanear is a device which convertspressure variations in air with audible frequencies into electric signals that travel to the brainvia
auditorynerve. Theauditoryparts of the humanear aregiven below:
The outer ear is called ‘pinna’. It collects the sound which passes throughthe auditory canal. Thereis eardrum at the end of the auditorycanal.
Whena compression of a medium reaches eardrum;it pushes eardrum inward. Similarly, eardrummoves outward when rarefaction reaches
there.In this wayeardrumvibrates. Thevibrations are amplified several times by hammer,anvil and stirrup, inthe middle ear . In the inner
ear thepressure variations are turnedinto electrical signals which furtheraresent to the brain and brain interpretsthem as sound.