IT is the form of energy which produces the sensation of hearing  and it felt by ears and law of conservation of energy is also applicable to it and it travels in form of waves .

PROPERTIES OF  SOUND   : Sound is produced  when object vibrate, it is produced by vibrating objects .

The energy required to make an object vibrate and produce sound is provided by some outside source such as clapping, sound of our voice  is produce by vibration of vocal chord in our throat or  sound produced by beating drum/ tabla due to vibration of membrane . In Laboratory the experiment sound  is produced by vibrating tunning fork. The vibrations of tunning fork can  touch a small pith ball / cork ball with the prong of the sounding tunning fork the pith ball is pushed away with great force

Sound can also be produced by vibrating strings of sitar /by vibrating air through flute/by vibrating the membrane of tabla or drum/ by vibrating the plates of bicycle bells/ by friction between to objects/by scratching or scrubbing the two objects.

PROPOGATION OF SOUND WAVES : Sound  require medium   of  propagation which may be solid ,liquid or gas. When  an object vibrates than the air particles  around it vibrate exactly in same manner and displace from their stable position. These vibrating particles exert the force on the near by particles so that they also begin to vibrate, this process continued in the medium till the produced sound reaches to our ears ,the disturbance produced by sound travels  through the medium but particles do not leave their position they transport the energy only

Wave is a kind of disturbances which travel  through medium and transport the energy so sound travels in form of waves so they are called mechanical waves

SOUND WAVES ARE LONGITUDINAL WAVES : when a body vibrates then it compresses the air surrounding it and form the aera of high density called  compression (C). It is the part of wave in which particle of medium are closer to one another  forming the high pressure. This compression moves away from the vibrating body when the vibrating body moves back as the aera of low pressure is created  which is called rarefaction (R) it is the area of the wave particles of the medium are further apart from one another forming low pressure and low density area. When body vibrates back and forth a series of compression and rarefaction are formed in air resulting the movement of sound waves .

vibrating body   C—-R—–C——R—–C—–R——C  ( sound wave motion)

SOUND NEEDS MEDIUM FORPROPOGATION : We know that sound waves are mechanical wave , needs medium  for it’s propagation it cannot travel in vaccum In an experiment  an electric bell is suspended  in air tight bell jar connected with vaccum pump when bell is  full of air we can hear the sound of bell  and air is pumped out of the jar by vaccum pump  no sound can be heard so medium is needed for the propagation of sound waves. ( fig from bk)

We cannot hear sound directly on moon as there is no atmosphere on moon for the propagation of sound the astronauts use wireless for conversation at moon .

SOUND WAVES  ARE LONGITUDINAL WAVES: A wave in which the particles of the  medium vibrates back and forth in the same direction in which the wave is moving is called longitudinal waves When we  push  and pull the slinky  compression  when number of turns are more closer  and  rarefaction when number of turns are farther . when the waves travel along the slinky  spring it’s each turn  moves back and forth by only a small distance in the direction of wave ,so the wave is longitudinal. The direction of vibrations of the particles  is parallel to the direction of wave.

TRANSVERSE WAVES : When the particles of the medium vibrates perpendicular to the propagation of waves . When one end of slinky is moved up and down rapidly whose one end is made fix. The upper end is called crest and the down end is called trough Light wave travels is transverse waves and do not require any medium or can travel in vaccum

CHARACTERISTICS OF SOUND WAVES ; The main characteristics  of sound waves are wave length (h)  ,frequency (n) amplitude (A) Time period (T)  and velocity  (v)

when wave travels in air the density and pressure of changes from the mean position, compression /crest with high density and high pressure and rarefaction/trough with low density and pressure takes place

WAVE LENGTH : Itis the  distance between the two  consecutive   compression or rarefaction in longitudinal waves or distance between  two consecutive crest or trough in transverse wave It is represented by lamda (Greek word ) SI unit metre

AMPLITUDE :  The maximum displacement of the particle from it’s mean position of the vibrating particle is called displacement . SI unit metre .

FREQUENCY : Number of complete  waves  produced in one second or number of vibrations per second is called  frequency (n)   frequeny = no. of vibrations taken in one second SI unit Hertz  . 1 Hertz means  one vibration taken in one second

TIME PERIOD : Time taken to complete one complete vibration by the vibrating body is called time period   T= 1/ frequency =1/n  SI unit second

VELOCITY : It is the speed with  which wave travel in the medium

velocity of wave = wave length / time period

v= h/T   as n= 1/T        V=hxn       Velocity = wave length x frequency

PITCH : The pitch  of sound depends on the frequency of sound/vibration. It is directly proportional  to frequency. Greater the frequency higher the pitch and lesser the frequency lesser the  pitch . The  voice of women is shrill which has high pitch  due to shorter  vocal chords  so it vibrate more frequently  and produce  higher pitch where as the voice of man has harsh voice due to larger vocal chords that vibrate with lower frequency  and  have low pitch. High  pitch  sound has large number of compressions and rarefaction passing fix point per unit time.

LOUDNESS : It depends upon the amplitude of the sound wave ,it is measured of the sound energy reaching the ear per second , greater the amplitude of sound  wave, greater is the energy louder the sound, shorter the amplitude lesser the  energy soft is the sound. SI unit decibel.

Loudness = k (amplitude)^2   that is if amplitude increase two time than loudness increase  four times .

QUALITY / TIMBRE : The timbre of  sound  depends on the shape  of the sound wave produced by it . It is the characteristic of musical sound. It helps to distinguish  between  two sounds of same pitch  and loudness . Sound of single/same  frequency  is called tone . and  mixture of different frequency  is called note

NOISE ;It is unpleasant sound to hear whereas MUSIC  is a pleasant  sound to hear and of good quality.

SOUND IN VARIOUS MEDIUM :  Speed of sound depends  on the nature of the material through which  it travels. It is least in gas , intermediate in liquid and highest in  solid . The speed of sound increases with increase in temperature , with increase in humidity  in air speed of sound is 332 m/s

Speed of light is faster than sound that is why lighting is seen before the thunders of clouds.

SONIC BOOM: Some  aircrafts bullets rockets  etc  have supersonic speed it refers to the speed of an object  which is greater than the speed of sound and produces extremely  loud  sound waves which is called shock waves in air . Sonic boom is an explosive noise  caused by shock waves which produce  tremendous sound energy which can shatter the glass panes of windows

REFLECTION OF SOUND :  Sound waves also bounces back  when it falls on the hard surface this is known as reflection of sound.  Laws of reflection of light is obeyed by sound (fig book )

i) The incident of sound wave, the reflection of sound wave and normal  lie at the point of incident  wave on same plane   ii) the angle of incident sound wave is equal to the angle of reflection of sound wave .

REFLECTION OF SOUND (ECHO) It is the repetition of sound caused by reflection of sound wave  is echo

We can hear echo when there is time gap of 0.1 second in orginal sound and echo .Itis produced when sound  is reflected back from hard surface as soft surface absorb the sound waves

To calculate minimum distance for echo is 17.2 metres

distance = (velocity of sound x time to receive the echo) -;-  2

Rolling  of thunder is due to multiple  reflection of sound of thunder from the number  of reflecting surfaces such as clouds and earth .

REVERBERATION  : It is the persistence of sound in a big hall due to repeated or multiple reflection of sound from the walls, ceiling and floor of the hall is called reverberation .If the distance is too long sound becomes blurred, distorted and confusing .

HOW  REVERBATION BE REDUCED : Panels made of compressed fibre board  are put on the walls and ceiling to absorb the sound. Heavy curtain are put on doors or windows , carpets on the floor.

APPLICATION OF REFLECTION OF SOUND: i) Megaphone, loudspeakers , bulb horn , trumpets, shehnai are made in way to send sound in one particular  direction without spreading around. All  these  have funnel tube  which reflets sound waves repeatedly towards the listeners.

ii) Stethoscope : It is the instrument used by doctors for listening the sound produced in human  body mainly by heart and lungs by means of multiple reflection .

iii) Sound Board  : In big halls / auditoriums  sound is absorbed by walls/ ceiling/ seats so  a curved sound boards are placed behind the speakers so that the speech can be heard  easily the board works on multiple reflection of sound on the other hand ceiling ae also made curved for this purpose .

RANGE OF HEARING : For human being it is   20 Hz — 20000Hz, child below 5 years and dog can hear up to 25KHz

The sound below  20Hz  is  infrasonic sound Rhinoceroses  can communicate at 5Hz Elephant and whales are also hear infrasonic waves ,  earthquakes  produces infrasonic waves before eruption that is why animals living underground leave the  their houses

The sound with the frequency above 20 kHz are called ultrasonic sounds.

HEARING AID  : It is  an electronic device used by person who are hard of hearing Microphone convert sound into  electrical signals than those are amplitude by amplifier. The amplified signals sent to speaker of hearing aid and speaker convert the amplified signals to sound and send to the ear  for clear hearing .

APPLICATION OF ULTRASOUND  : It is used to detect the cracks  in metal blocks in industry without damaging it . It is used in cleaning the aera which is hard to reach /odd shape difficult to clean   It is used to investigate the internal organ of human body such as liver/ gall bladder/ uterus etc  It is also used in  echo cardiography and ultra sonography .

SONAR ; It is sound navigation and ranging device which is used  to find distance , direction and speed of underwater objects. It consist of transmitter and receptor which is installed at the bottom of ship ,The transmitter produces   and transmit ultrasonic waves and these waves travel through water and after striking the object  at the bottom  is reflected back and received by detector .

The reflected waves  are converted into electrical signals by the detector the sonar  measures the time taken by ultra sound waves to travel from bottom  of sea  and back to ship

distance of the object at the bottom of sea =(  velocity  x time )-:- 2

APPLICATION : Bats fly in  the dark night by emitting high pitched ultrasound waves which are reflected  from the obstacles/prey and returned to bat ear the nature of reflection tells the bat where the obstacles or prey is what it is like this is called bio sonar .

STRUCTURE OF EAR  :  Ear consist of three parts outer ear, middle  ear and  inner ear . The ear are the sense  organs which help in hearing sound the outer ear is called pinna  It collects the  sound  and passes the auditory  canal at the end of auditory canal is a thin elastic membrane which is called ear drum/ tympanic membrane. ( fig from bk )

The middle ear  contains three bones  hammer, anvil and stir up linked with one another free end  of hammer touches ear drum and that of stirup linked with membrane of oval window of inner ear  .The lower part of the middle ear has narrow Eustachian tube

The inner ear is coiled tube called cochlea  which is connected with oval window which is filled with liquid containing nerve cell connected to brain

WORKING of human  ear : first  sound waves  reaches to Pinna than to ear canal  which makes the ear drum vibrates  it goes to hammer than to anvil after that to stirup  which final goes to oval window  than to cochlea than to auditory nerve  finally goes to brain which interprets the electrical siganals as sound  and we get the  sensation of hearing .

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