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sound class 9 notes |guide for class 9 science| Science-universe

sound class 9 notes |guide for class 9 science| Science-universe

 Class 9 science chapter sound question & answer:

 

 Sound and vibration definition:

sound meaning

In our daily life we hear many sound around us from humans, animals, birds vehicles etc.But did  guys ever thought, what sound is ?

Well the correct answer is that sound is form of energy that makes a sensation of hearing in our ears.

 On the other hand  vibration can be defined as the to and fro motion motion of any body and that to and fro motion is the key factor for the production of any kind of sound.Lets discuss about deeply in the below topics.

 

How is sound produced ?

how sound is produced
 Sound is produced by the vibration of an object.To understand the phenomenon, lets us illuminate an example.Let us take  the example of an guitar. In  this case, when the guitarist play the guitar, the strings of the guitar produces vibration, which results the production of sound from the guitar. The amount of sound produced will be dependent on the amount of vibration, the guitarist on the strings.

 

Propagation of sound: 

sound needs a medium to travel


From the above discussion we came to know that how sound is actually produced, now lets try to find out how does sound actually propagate. Well in order to propagate, it needs a medium in which the propagation must be proceed.(Medium is kind of any object/matter/gas through which sound travels). We know that sound travels in form of wave i.e. mechanical wave & its speed varies in various medium.

Types of sound: 

 Depending upon the range of frequency of sound in hertz, the sounds are classified:(Hertz is the the SI unit of sound & it is denoted by the symbol Hz)


i) Sonic: These are the sound wave  which have frequency range from 20 Hz to 20,000Hz. This range  is also known audible range. Humans can only hear sound from
this range.

  

 


ii) Infrasonic sound: This are the sound waves, which have frequency below 20Hz.

                                      Infrasonic sound examples are the sound produced by Rhinoceroses,whales, elephants for communication, 

 


iii)Ultrasound: This are the sound waves which have a frequency higher than 20,000Hz.

                               Ultrasound examples are the sound produced by dolphins,bats.

 

Speed of sound in different medium :

sound speed in aluminium
From the above discussion we came to know that sound needs a medium in order to travel from one place to an another. Now lets discuss its speed in  various medium.The speed of light depends on that particular medium its propagate, it may be solid/liquid/gas. The speed of sound is lowest at gas, the speed of sound is  more liquid as compare to gas and the speed of sound is highest in solid specially in Aluminium at a speed of 6420m/s.In short sound travels fastest in Aluminium,

 

Can sound travel in vacuum ? :

sound in space
We know that sound is  a kind of mechanical wave,which needs a medium in order to travel from one place to another. But did sound can also be traveled in  vacuum ? Lets try to figure out the solution with the help of an example.

Lets  take the example of an astronaut. Did you guys astronaut wear up a white suits, when they out from their space ships. Well they don't get oxygen in space, but they also cannot hear among themselves in space, that is why the helmet which they is not just for the breathing and expelling out carbon dioxide, but also for their communication through radio wave, though they may be physically very close to themselves.

Hence we can conclude that sound needs a medium to travel

 

sonic boom:

supersonic jets
We know the sound waves  travel through any medium with finite speed.But what if that particular object(medium) that travels even faster than sound ? In such situation that object is said to be traveling at supersonic speed and it produces a shock waves in air, which carry a large amount of energy.Hence  the air pressure associated with this type of shock waves, produces a very sharp and loud sound, which is known as sonic boom.This kind of  shock waves are produced by supersonic aircrafts  which have the capacity to shatter glass and could even damages the building.


Reflection of a sound :

We know that light follow the principles of reflection.But what about sound? Well the answer is that like light, sound also follow the rules of reflection. In which when a sound waves, hits the surface of solid or liquid, it exhibits same phenomenon, as light exhibit.The wave is reflected back by the surfaces by creating angle of incidence with angle of reflection, thereby making equal angles with the normal.

Now it may be confusing to understand the phenomenon.So lets try to illuminate it  by considering an example. Lets take the example of a echo.

Echo:

When we stand on a mountain and shout loudly or scream, we hear that particular sound again and again for a few moments, that particular phenomenon is called Echo. In order to hear an echo the time travel between the original sound and the reflected sound must be at least zero.

echo test

                                    

Reverberation: 

Sometimes we may also hear more than one echo,that is due to multiple reflection of that particular sound. For example, when a sound is produced in a large auditorium, we hear echo  or reflection of sound in multiple times, until the sound is reduced to its value, which is no longer audible.Such type of repeated reflection that causes persistance of sound is known as reverberation.

reverberation meaning

                     

 Uses of multiple reflection of sound :


i) This technique is used in  horns of vehicles and motor bike where people hear multiple sound with reflection.                                    

multiple reflections

 ii)The stethoscope uses  for checking of heart beat of a patient, is also an application of multiple reflection of sound.In which the heart beat of patient reaches  to the ears of doctor through multiple reflection.

stethoscope is used for

                    

iii) We have seen that the ceilings of cinema halls and the conference halls are curved in shaped, it is  because so that the  the sound waves hits the  ceilings and produce multiple reflection.

what is multiple reflection

                                      

Application of ultrasound:

 i) It is used in industries to detect cracks and flaws in metal blocks,specially in buildings.

                                                    what are the applications of ultrasound                        

 ii) Echocardiography: Echocardiography test is an popular technique in which we get the image of heart,where ultrasonic waves are made to reflect various organs of our heart and form the image.

echocardiography test means

                                                                                  

  iii) Ultrasonography :  An ultrasound scanner is used in  this technique, which uses ultrasonic waves to get the images of internal organs of an human body.

ultrasound scanner

         Ultrasonography test is used in  purpose of detecting the  stones in gall bladder and kidney and also the tumors in different parts of the body.Here, the ultrasonic waves are traveled through the tissues of the body in such a way that it detects if there is any change in tissues density.Thereafter, these waves are then converted in electrical signals, which are used to generate images of body organs, which get displayed on  a monitor.

iv) kidney stone treatment :Ultrasound is also used in in the  treatment of  small kidney stones where, they are fined into grains by the effect of ultrasonic waves and later the stones are flushed out through urine.


Sonar : 

It is an device  that uses ultrasonic waves in order to calculate the distance, direction and speed of underwater objects. Sonar full form is Sound Navigation and Ranging.

Sonar uses :

Sonar is made of transmitter and a detector, which is installed in submarines, boat and ships. The sonar system is used  to detect any kind of upcoming objects like glacier , enemy submarines,  hills,valleys,boat, ships etc.

what are the applications of ultrasound

     Here, the fitted  transmitter  produces and transmit ultrasonic waves. The waves traveled in underwater and after colliding with the object on the seabed, it got reflected back and are sensed by the detector. The detector converts the ultrasonic waves into electrical signals which are approximately interpreted . The distance of that particular object that reflected the sound wave can be measured by getting the speed of sound in water and  the time taken during the transmission and reception of the wave.

 

How do bats fly safely in darkness ?

 Ans:-Bats can fly in dark because bats emits ultrasonic waves and detect reflected ultrasonic waves. So they emit waves, the waves after striking with any obstacles in front of bats, gets  reflected.The reflected waves are then detected by the bats. In this way bats fly at night.

how bat use ultrasound



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Sound  class 9 solutions:

1) What is sound and how it is produced Class 9 Ncert?

       Sound is form of energy that makes a sensation of hearing in our ears.

        Sound is produced by the vibration of an object.To understand the phenomenon, lets us illuminate an example.Let us take  the example of an guitar. In  this case, when the guitarist play the guitar, the strings of the guitar produces vibration, which results the production of sound from the guitar. The amount of sound produced will be dependent on the amount of vibration, the guitarist on the strings.


2) What is sound 9th class?

     Sound is form of energy that makes a sensation of hearing in our ear It is produced by the vibration of an object.(vibration can be defined as the to and fro motion motion of any body and that to and fro motion is the key factor for the production of any kind of sound).

 

3) What is frequency of sound class 9?

        Frequency  of sound can be defined as the  number of oscillation of object in per unit time.   

                                                                                    

4) What are the 3 types of sound?     

Ans:- Depending upon the range of frequency of sound in hertz, the sounds are classified:  

          i) sonic sound waves          ii) Infrasonic sound waves  & iii) Ultrasonic sound waves .

 

5) What is reverberation Class 9?

Ans:-  Sometimes we may also hear more than one echo,that is due to multiple reflection of that particular sound. For example, when a sound is produced in a large auditorium, we hear echo  or reflection of sound in multiple times, until the sound is reduced to its value, which is no longer audible.Such type of repeated reflection that causes persistance of sound is known as reverberation.

      

6) How is ultrasound used for cleaning class 9th?

Ans:- The object which need to be cleaned are dipped in cleaning solutions followed by emitting ultrasonic waves into it. Due to the high frequency of ultrasound  of it the dirt,grease,and dust particles are separated and drop out. Thus that particular object is cleaned.

 

 









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