sound - chapter 12 ncert science for kv students

SOUNDTANAY SHUKLA IX B

DEFINITION

•Sound is a form of

energy which produces a

sensation of hearing in

our ears

PROPAGATION OF SOUND

•Sound is produced by vibrating objects.

•Sound is transmitted through a medium.

•Medium can be solid, liquid or gas

•It moves from point of generation to the

listener.

•When the object vibrates, the particles in the

medium around it start vibrating.


•There is no movement of the particles, they

don’t travel.

•The particles are displaced from their

equilibrium state.

•The particle exerts force on the adjacent

particle.

•The adjacent particle gets displaced while the

previous particle returns to original position.

•This process continues till the sound reaches

SOUND WAVE

•Wave is a disturbance that moves through a

medium.

•The wave is created when particles set

neighbouring particles into motion.

•Since the particles of the medium are in motion,

Sound wave is a mechanical wave.

MECHANICS OF SOUND WAVE

•Air is the most common medium through which

the sound travels.

•Forward movement of vibrating object compress

the air, creating high pressure, this is called

Compression (C).

•The compression moves away from the vibrating

object.

MECHANICS OF SOUND WAVE•When the vibrating object moves backwards it

creates low pressure called the Rarefaction (R).

•Pressure is related to the number of particles in

the medium in a given volume.

•The denser the medium the more the pressure.

•Thus sound propagation is a propagation of

density variation or pressure variation in the

medium.

SOUND AND MEDIUM

•Sound being a

mechanical wave

needs a medium.

•It cannot travel in

vacuum.

SOUND – LONGITUDINAL WAVE

•Sound waves are longitudinal waves as

:-

•The individual particles move in a

direction parallel to the propagation of

disturbance.

•They oscillate back and forth about their

position of rest.

•Hence it is a longitudinal wave.

SOUND – LONGITUDINAL WAVE

CHARACTERISTICS OF SOUND WAVE

•Sound wave can be described by its

:-

•Frequency.

•Amplitude.

•Speed.

WAVELENGTH DEFINED•In case of Sound waves the distance between two

consecutive Compressions (C) or two consecutive

Rarefaction (R) is called the wavelength.

•Wavelength is denoted by Lambda.

•The SI unit of wavelength is meter (m)

WAVELENGTH DEFINED

FREQUENCY DEFINED•Frequency tells us how frequently an event

occurs.

•In case of Sound waves it is the number of

Compressions (C) or number of Rarefaction (R)

per unit of time is called the frequency of the

sound wave.

•Frequency is denoted by nu.

•The SI unit of frequency is hertz (Hz)

FREQUENCY DEFINED

TIME PERIOD DEFINED•The time taken by two consecutive

Compressions (C) or Rarefaction (R) to cross a

fixed point is called the time period of the wave.

•Time period is denoted by T.

•The SI unit of Time period is second (s).

•Frequency and Time period are related as

• Frequency = 1/ T

TIME PERIOD DEFINED

PITCH OF SOUND

•The faster the vibration of the source, higher is

the frequency and thus higher the Pitch.

•A high pitch sound corresponds to more number

of Compressions (C) and Rarefactions (R) passing

fixed point per unit time.

PITCH OF SOUND

AMPLITUDE DEFINED•The magnitude of maximum disturbance in the

medium on either side of the mean is called

Amplitude.

•Amplitude is denoted by A.

•The Loudness or Softness of sound is

determined by its Amplitude.

•It depends on the force used to produce the

vibration.

•For sound its unit is that of density or pressure.

AMPLITUDE DEFINED

TONE, NOTE, NOISE DEFINED

•A sound of single frequency is called Tone.

•A sound of mixed frequency is called Note

•What is pleasant to listen is called Music.

•Noise is unpleasant to the ear.

SPEED OF SOUND IN DIFFERENT MEDIUM

•The sound propagates through a medium at a

finite speed.

•The speed of depends on the properties of the

medium. It travels faster in a denser medium.

•The speed of sound depends on the temperature

of the medium. It increases with rise in

temperature.

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Oxygen Air Helium Hydrogen Methanol Ethanol DistilledWater

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Speed of Sound in Different Medium

REFLECTION OF SOUND

•Sound follows the same laws of reflection as

light.

•The angle of incident sound wave and the

reflected sound is equal with the normal to the

reflecting surface.

•The incident wave the normal and the reflected

wave lie on the same plane.

REFLECTION OF SOUND

ECHO

•Echo is the reflection of Sound from buildings

and mountains.

•To hear an Echo the difference between the

initial sound and the reflected sound should be

at least 0.1 sec.

•Mathematically this distance travelled by sound

should be at least 34.4 m on an ambient

temperature of 22 degrees centigrade.

•

REVERBERATION

•Repeated reflection of sound that results in its

persistence is called reverberation.

•Excessive reverberation prevents perception of

sound.

•Reverberation is controlled by covering the roof

and walls of auditoriums with sound absorbing

material.

•Fibreboard, rough plasters, cardboards, and

REVERBERATION

USES OF MULTIPLE REFLECTION -SOUND

•Megaphones are used to amplify the sound.

•Doctors use Stethoscope which has pipes where

multiple reflections take place.

•Curved ceilings of cinema halls are used to

ensure that sound reaches to all the audience.

•Soundboards are used behind the stage to reflect

the sound.

USES OF MULTIPLE REFLECTION -SOUND

RANGE OF HEARING

•Audible range for human beings is from 20 Hz

to 20000 Hz.

•Younger children and few animals hear beyond

this range as well.

•Sound below 20 Hz is called Infrasonic. (Rhinos,

Whales)

•Sound beyond 20000 Hz is called Ultrasonic.

(Bats, Dolphins)

RANGE OF HEARING

APPLICATIONS OF ULTRASOUND

•Cleaning of hard to reach places of machines.

•Detect cracks and flaws in metal blocks.

•Medical application in echocardiography.

•Ultrasound imagery of internal organs of human

body.

•Removal of kidney stones by breaking them with

ultrasound.

APPLICATIONS OF ULTRASOUND

SONAR

•SONAR stand for SOund Navigation And

Ranging.

•It uses ultrasonic waves to measure distance,

direction and speed of underwater objects.

•It has a transmitter and a detector collectively

called Transducer.

•Mathematics of distance calculation is 2d = v x t

STRUCTURE OF HUMAN EAR

sound - chapter 12 ncert science for kv students

Science