hello friends this feature on sound fat one is brought to you by exam few dodge Koch no more fear from exam effects to be covered in this lesson our introduction production of sound propagation of sound sound waves and longitudinal characteristics of sound waves speed of sound reflection of sound range of hearing and human ear structure and function along with applications of ultrasound so what do you think are we going to study in this lesson on sound so whenever is sound there are so many things that come to our mind I mean I really don't need to introduce this lesson you know what do I mean when I say sound there are so many different kinds of sounds which we actually hear right in fact right now I'm speaking that makes sense because you are able to hear it because of the sound which is being produced by me is being heard by you that's how it makes sense right sonography we think of any sound we think of the music which we hear it might be a musical in the movie it can be the music produced by a musical instrument like a flute or a guitar or the band party which goes generally during the Indian weddings right the Baraat which goes during Indians wear at weddings or the sweet voice of the couple or if you think of the Bell whether it's the temple Bell or your schoolbag so the do the ringing of the Bell is again a kind of sound which we hear when somebody is talking like the way I am talking right now and you are able to hear so that is again a sound even try this one example you stretch a rubber band and leave it you get a sound slight sound right so if you think of sound there are so many different varieties of sounds which we actually come across in our day-to-day life right so in this lesson we are going to talk about some we're going to see how is sound actually produced from the others the sound del is produced how the sound reaches from one person to another for example right now I am speaking and you are able to hear so how is the sound getting transmitted so we'll talk about the production of sound we will talk about the propagation of sound we will also talk about the various properties which actually characterizes a sound right so this lesson is all about sound okay so with this let's start from the very basic and the basic question is what produces sound so how is the sound actually produced so did you notice something in the examples which I cited in the previous slide let us look at those examples once again let us look at this guitar how do you produce a sound with the help of a guitar it is suppose if I keep a guitar on the table will it start producing some will I be able to hear the nice music from the guitar no unless and until you move the strings of the guitar you will not hear any sound right so in a guitar the sound is produced by the vibration of the strings so these guitar strings which you have a guitarist will do what he will actually move this strings right okay next if you look at the belly how does this velcro do sound here what if you would have gone to a temple you would have seen that this thing which you have in the Bell this one so then you move it what happens it starts vibrating it starts moving and because of its movement the sound is reduced similarly when you an example of somebody speaking then somebody speak how was the sound produced in the vocal chords I mean if you look inside the human structure in our vocal chords the vocal chords actually vibrates and because of that by raishin the soundest reduce if you do not buy read back no sound hypocrite rooster said literally the best example for you to understand you take a rubber band in your hand it will not make any sound but when you stretch it and then give it it makes a sound that is again because of the vibration so the bottom line is that sound is produced by vibration of objects so I hope all of you are clear with what is vibration right vibration the term vibration engine literally it means something which is shaking so vibration is nothing but a rapid to and fro motion of an object so that means an object is swinging between two positions right left right left right left so when that to and fro motion takes place very rapidly we see that the object is vibrating so sound is always produced by vibration of objects so now if you look at any of the examples which I gave in the previous slide everywhere you will see that there is a vibration which is responsible for the production of sound right we are good to go okay so with this let us now talk about the propagation of sound that means how does sound travel okay so we understood that when some object vibrates sound is produced fair enough so now the sound is produced in the guitar but how does that sound reaching the from the guitar to the listeners ear so how is that sound traveling from the guitar to your ear that is the next question so let us try to understand how sound propagates so sound propagates through a medium so again you have a new term here here medium so what does this medium knock through which sound will travel so let us look at some of the examples before that it is try to understand what is a medium an object through which sound is transmitted that means in order that the sound is able to reach from one point to another you mean some object which will carry the so that object is nothing but media let us look at this example let's suppose if there are two boys this boy is speaking something so the sound is travelling to this guy so how is the sound traveling through the medium what is the medium here here there is a broad kind of a structure but inside the rod what do you have to carry the sound it is nothing but air right even if you don't have this tunnel like structure even if the sky spins and this guy hears it is like the sound is being traveled through the air so air is a medium by default correct so how actually the propagation of sound takes place through this medium now this medium can be a solid or a liquid or a gas so that means that is so sound can even travel through a liquid sound can even travel through gas and it can travel through some solid object as well right so tell me anything now the question is how is the sound getting propagated through an object so this is the example when we talked even in that case air acts as a default medium so air is not the only medium through which sound can travel they remain with the medium for example you can think of and solid object for example let us suppose you are in one room and your friend is in the other room so when you speed from this room your if you speak nitin loudly your friend is able to hear that's because sound is able to travel through the solid medium that is to the one so the wall is not acting as a barrier your friend is also able to hear you he that means that sonic substance is acting as a medium so there are many different mediums that can be so a liquid of gas but air is by default a medium which helps in propagation of sound but the important point here is that sound needs a medium to propagate if there is no medium sound will not be able to properly so we will talk about that part also little later so right now let us try to see how actually the propagation of sound takes place how actually the sound is transmitted from one point to another so here we have taken an example of a speaker let us say this is the source of some so this object is producing sound and this is the ear of the listener so this is the person who is listening so how will some traveling from this point to this point Takas a question so what happens in this case is sound is produced here because of some vibration right there will be some library sheet a convinced consent so as a result then some vibrations in this object as a result particles of this medium which are in direct contact with the object gets displaced from their equilibrium position let us suppose let me draw a rough diagram let us say this is my object records the source right so this object vibrates so vibrates means it will move like this it'll come back like this again it will move like this it'll come back like this so this kind of to and fro motion is known as vibrations so this object vibrates so when this object comes this side it is suppose there is a particle one so this particle is nothing but these are the particles of the medium so we assume that if the medium is air so air will have so many particles in it right suppose there is one particle in the air which is in the neighborhood of this object so this particle will also get pushed in this direction right so now so the particle one gets displaced from its equilibrium position so now this particle will exert some force on another particle later suppose there is some particle to here so this particle one will exert some force F on this particle right now after exerting this force F on particle to this particle one will come back to list right so by moving the side it came back right when one went to this side it pushed two so to again vent the second so what we'll do is exert some force F on particle three so it will exert some force on particle three and again it will come back so as I designed this particle three will start moving in this way so what do you see tell me what is happening so every particle of the medium is actually vibrating they are actually moving on its own position so that means every time this this object is also vibrating so it will keep will coming this side they're going back this side again coming this side going by the same so every time this object is coming in the right direction it is pushing one to right one will push two to right - will push three - right so as a result every object is vibrating or it is oscillating in its own position but as a result this vibration on this disturbance this is a kind of disturbance right because of the vibration of the source there is a disturbance which will keep on moving from particle one into particle to particle 3 because this disturbance is getting transmitted and this disturbance is nothing but sound so if you look at this diagram very carefully you will see that just observe any one particle you'll be able to when you look at this picture what do you see you feel that you can see very clearly that the disturbance is moving along this direction right so this disturbance which you see I mean you do not see the particles individually you just look at this picture as of hold what do you see you see you it looks as if everything is moving towards the right side so that is the disturbance which is getting transmitted this disturbance which I told you this object pushed one one pushed two - pushed three three pushed four so the disturbance is actually moving towards the right direction that is known as propagation of sound but when you look at each particle of the medium just observe any one particle for example it let me take this particle that is one particle here if you look at only this particle do not see anything else what do you see how is the particle moving the particle is not going anywhere it is just oscillating about its mean position once it is going right who wants it is going left once it is going right once it is going left similarly you look at any other particle let me consider this particle now if you look at this particle this particle is again oscillating about the red dot right so every particle of the medium none of the particles are actually moving from one point to another so the particles of the moon' medium and helping the sound sound is nothing but the disturbance it is actually helping to transmit the disturbance through the neighboring particles but the particles of the medium do not move as such ok so what is the conclusion the first conclusion is that particles of the medium do not move forward themselves even though it appears that a disturbance moves forward but the particles of the medium do not move forward right second is disturbance establish forward through the particles of the medium so here the disturbance is started forward so these are two different things one thing is the particles of the medium what are they doing they are just awesome eating they are just vibrating about their mean positions but as as a whole if you look at it the entire disturbance is getting transmuted and this disturbance is nothing but sound right so what do we see so this disturbance is the sound and that sound is again a wave so this shows that it is nothing but a wave sound when I talk of sound sound is nothing but a sound wave actually so it sound is a form of wave so what does me if I am sure all of you know what is we bean is nothing but it is a disturbance in a medium see if you do not have the source of sound there will be no disturbance in the medium the particles will not oscillate at all so if the particles do not oscillate there will be no sound but wave is something wave is a disturbance which is created in a medium by some external source so here the external source is the source of sound that is the speaker right so it was a source which created a disturbance in the entire medium so this disturbance is known as a wave and here the kind of wave which we have gives some sound wave so now you understood how some propagates some wave propagates through the particles of the medium but the particles of the medium do not move themselves they actually oscillate about their mean positions and as a result the disturbance or the sound is carried forward to the particles of the medium let us now talk about compressions and very factions of a sound wave now let us see what our compressions and rarefactions let's take the same example what is happening here the sound is getting transmitted from the source to the listener right so what are compressions compressions and rarefactions are the two terms which are used to characterize sound wave so what are compressions compression means something which is compressed the term itself means something which is compressed something which is very congested right so here if you see there are certain regions now when the object moves left think of what we discussed in a previous slide how is this movement happening when this object vibrates what happens let us suppose when it move forwards it pushes the neighboring particles right so when it pushes the neighboring particles it is actually compressing the region in the front that means let us suppose let us understand it in this way it is suppose if this is my object if this is my source so when it vibrates and it moves in this direction what is happening let us suppose if these are the particles of the medium so this will move the side so it will actually compress the particles here so the particles will come close back right again when this object comes back when it comes backwards what happens this particles and wide away from each other they are not compressed now so the when they are compressed that means when this object moves forward in that case the neighboring region becomes a region of high pressure or we can see that the density of the particles is high if you look at it here you can see that when this particle moves in this direction what happens a high compression region app exists here that means a high pressure region so the region where the density of particles is more the region where the congested condition is more it is more congested right so if you look at this figure as a whole you will see that there is one region the particles are more congested there is one region where particles are wide away from each other so the regions of high pressure or high density is known as compression and the region for loop of low pressure and low density is known as very airy faction so these are the two very important terms compression and rarefaction so combinations happen when the object vibrates in the forward direction because when it vibrates in the forward direction it exerts a force in the neighboring particles as a result a neighboring particle comes closer so the density of particles increases that at that time it has more pressure so it is high pressure high density that is called compression similarly when the object moves backward so then there is less pressure on the neighboring particle as a result the neighboring particles can move away from each other so a region of low pressure is created and that is known as the Rayleigh faction so in this case we can say that this is compression I mean if if you do not take an animated figure of this so you can say that this is this is compression and this is really faction again this is compression again this is really fashion so you have alternative compeition and very airy factions so in really faction you see the particles are quite away from each other but in compression they are very close to each other so come from the term compression you can remember compression with something which is compressed so when you compress something all the particles will come very close by so the density of the particles will be more so the pressure will also be more right so that is how you can remember what is compression and what is very refraction now as I mentioned before also that we we spoke about that sound means a medium to travel or to propagate now can some travel without a medium that is a Pacific device hammer medium if there is no air no water no solid object nothing so do you think that sound can travel without the medium can sound travel through a vacuum vacuum means an empty region where there is nothing not even here so that is well as vacuum the sound means medium to propagate it cannot propagate through vacuum so that means medium presence of a medium is a must for Soundwave so how was this room to prove this there was an experiment which was performed which is popularly known as the bench our experiment so what was this bench our experiment in this what was done was that an electric bed so you can see here it is an electric band if you press it sound should come right so this electric Bell was placed inside an airtight glass jar so this is the chair and inside the child we had this electric bench that is why this one has been join experiment okay so this was airtight so you cannot enter into this yes right and then this was connected to that this jar was connected to a vacuum pump so that means it is a pump which if you switch it on so vacuum will start entering inside vacuum will start entering inside means air will keep going out so gradually after some time it will be all vacuum there will be no here at all correct now what was saying that as vacuum was pumped in air was pumped Pumped gradually that is obvious what was observed is that the sound of this Bell became dimmer that means as more and more vacuum pump then the sound of the Bell started becoming dimmer and at a certain point of time when there was no air inside and it was all back soon the sound of the Bell was not at all heard so what did that prove that proved that sound cannot travel through vacuum so it actually means the medium and that despite that makes sense also because we saw that how sound propagates it actually propagates because of the vibration of the particles of the medium so if you do not have a medium that means you do not have the particles of the medium if you do not have the particles of the medium then how and how the song propagate there is nothing to vibrate right because normally how it is getting propagated is getting propagated because of the vibration of the particles of the medium so the particles are vibrating that is how they are making the neighboring particles also vibrate so if you do not have a medium you do not have the particles at all so the sound will not be able to propagate so that is why we say that sound means a medium it medium is a must for sound to properly thank you please 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