 they will probably join in some time yes good evening everyone fine so today is a session mainly on a communication system all right now this is a small chapter which could probably get over in two two and a half hours fine so whatever time will be remaining we'll be doing some problem practice of some random topic maybe we can take our fluids or we can take more emphasis itself whatever okay so first of all we will complete this chapter and you might be aware that this is the last chapter of our this thing from Sentom okay so once we complete communication system then we have completed entire curriculum of your J mains okay so then we'll have some time to probably plan out probably will be taking up a few chapters and solving questions on them fine and then the crash scores will start once maths and chemistry syllabus also gets over fine physics revision probably you can say starts little early and I can extend the revision a lot more fine then so let us start this chapter first once this chapter gets over then we will understand what to do by the time maths and chemistry syllabus gets over so we can plan out what to do in that period okay so let us start this chapter all of you write down the chapter's name communication system I don't I'll reshare so this is the last chapter all of you write down this chapter name communication system now communication the importance of communication I cannot you know talk enough about it how important the communication is okay so first of all you know you can say most primitive form of communication might have happened between probably two animals or two humans any testing any two living entities the communication could have happened like you know the food is there let us go there that's a sort of communication okay so suppose in earlier days when the language was not invented or discovered during those days people used signals by using hands gestures so you can understand what the other person is talking about and that way you can probably understand it fine now this kind of communication works really well if you have to communicate gesture I have not even started the chapter okay I'm just telling you importance of communication gesture works very well if you have to communicate quickly and have to send some targeted input okay for example you know nowadays also communication with your device suppose you have a mobile phone in which if you just wave off from your hand near your camera a screenshot will be taken automatically okay that is a gesture communication suppose you have to take screenshot and gesture communication is not enabled on your mobile phone then probably you may have to give command find out what is the keys that you press and then the then the you know screenshot will be taken so you know this is most primitive form of communication gesture and now we have also understood the importance of gesture communication because it can be very quick and works very well if you have to communicate a very targeted this thing message a short targeted input fine but then as the time go went by then of course the communication will not remain only you know very very targeted input it'll not be just like various food and things like that you would like to discuss everything in detail okay then you need help of language okay so then languages like and languages like a code which you create a sound so a person in front of you understand what is a meaning of that sound so there are set of rules for every language so if you if you talk in English so if if I and you both understand the rules of the English then you will understand whatever sound I'm making in English you'll understand what is the meaning of it fine so that is a reason why the language has evolved because it will let you communicate very very you know detailed manner and describe everything in pretty much in detail fine so then language came okay now when language came language again has a long long history there are different kind of languages there are these languages like Chinese languages which have many many you can say just like alphabets Chinese have this Chinese languages like you know they communicate in in form of pictures which is very primitive then you have Sanskrit language English language Hindi language all these languages got evolved and that helped us to communicate fine so you can communicate effectively now you can communicate in detail fine so this kind of thing has evolved and the limitation of you know the fact that whatever I want to communicate I can use the language and communicate exactly that okay the way I am probably I want to communicate whatever I have to say I can use the language and communicate it in a very detailed manner okay so it was a very very important thing to have language but the limitation still was what if what if I want to communicate if I want to to communicate to someone communicate with with someone who is 100 kilometers away let's say two kilometer away also okay so I want to communicate someone which is 100 kilometer away and I want let's say to communicate 100 people at once and those 100 people are living different different places for example you know you guys are definitely scattered in the Bangalore right different different places you guys are living you're not there at a single place still I am able to take the class and communicate with all of you okay now how effectively I'm able to communicate it also depends on how effectively you're listening to it and how many doubts you ask right so it has many factors in it but talking about just clear and simple communication point of view even though language was discovered still there were these two basic challenges okay and apart from these challenges there were you know challenges like probably suppose if I want if I want to send let's say images videos okay so basically language is fine but using language suppose I have to describe whatever pics I have taken I have to communicate that to someone so if I use language to start detailing the photograph I have taken the it will be a very very difficult thing to do okay so the best thing would be sending the image as it is or sending the videos as it is so there are many many limitations so the first limitation was of course the speed how quickly you can communicate okay then comes the quality of the communication quality included whether you are able to send only text whether you can send image also or you can send videos as well okay quality also includes how far you can communicate effectively or with how many people at max you can communicate so there are many many challenges okay so I don't know whether you guys aware of it but few years back probably 20 to 25 years back having a telephone was a luxury okay it was not that everybody had a telephone and even if you get an incoming call you will also get charged for it those who are calling and those who are receiving both used to get charged so we have come a long long way with respect to how we are communicating okay so you know the most primitive let's say the most you can say a systematic way of communicating with a strategic arrangement it is documented with how Akbar has done the communication so when Akbar used to fight for wars of course most of the time these guys will be fighting wars only during those times the wars was happening every now and then so Akbar used to spend most of the time outside let's say 10 kilometers away from his let's say wherever he used to recite so when his wife was about to deliver a child Akbar wanted to know whether it is a boy or a girl okay so what Birbal did he had arranged a set of drummers okay maybe let's say after every 20 to 30 meters there were drummers and depending on how the drum beats are there Akbar will understand whether it is a boy or a girl so first drummer will beat in one way then that will be heard by the second one third one fourth one like that the beats will reach to the Akbar like that Akbar will know now Akbar only wanted to know whether there's a boy or a girl because Akbar knew that he can't discuss anything else he can't use drum beats to communicate with with probably his wife and ask okay how is the health how much is the weight of the kid and you know so many many other things that who are there as is everyone happy and all that he can't use drummers to communicate all that in detail so of course you can understand Akbar during that time was a very very prominent figure even he was struggling and he could only get to know whether it's a boy or a girl by using some code messages fine so communication has always been a challenge whether you are a rich person or a poor person okay so it has become it during that time it had become a basic requirement okay basic need it had become and I'm talking about let's say I'm talking about what I'm talking about these whatever example I've taken I'm talking about the informal one okay suppose you have wars okay war is happening between the two countries alright then the army has to communicate to the base station right as in how many soldiers have how many soldiers lost their life how many are let's say injured and how much food is left what what all things they need whether they need some more doctors to cater to everybody so all that communication has to be done and then when when the war is happening they also exchange a lot of strategic input by using communication system only now when they use communication system to to exchange this confidential information then it has to be very very let's say very very properly it should be encrypted and then it should be a very very secure line of communication otherwise there is always a chance that your enemy will intercept your communication and decrypt and all those things your your enemy can do and will understand okay how many ships are coming now or from which side your army is and how they are traveling what is the plan and everything will be you know if they if you intercept the communication itself so you might not know that when Cold War was happening between Russia and the America not Russia USSR okay when Soviet Union was there so lot of people were employed only to intercept the communication and understand what is the communication going on because when you have a confidential information you will not use English to communicate you will create some some strange kind of way to communicate okay so just a simple this thing will be you will call like basic you will be saying like this you will write in reverse this is a very very you know very very simple way of encrypting this is also basic need only if you understand how what I mean okay then every word if I reverse you will know that it is written in reverse order you will decrypt it and you'll understand what is the communication going on so lot of things went by to make sure that communication is proper the system which you put the communication system you put is as per the requirement and as per whatever is suited for that this thing and you know most of the development that happened in the communication has happened in past you can say 30 to 40 years only so just go back little bit let's say 20 30 years back people used to have pager pager is a short SMS which you can send then you then people were using the landline phone then comes the cordless phone then comes the mobile phone then you have satellite phones so and then you have maybe you have this dish antennas wherein you can catch the signal and you can broadcast a single thing suppose I have to broadcast an important message let's say Modi has to do monkey bath right chapecha and whatever he does he will be using radio station or he will be broadcasting his message and you can see that entire country get that message at once that is you know that is because of some communication system only so communication system is a very very important part and it is much needed you can imagine how quickly you know in our time we in our time as in when I was in let's say I was doing my first and second year of engineering we used to think that email is a luxury when Gmail came you cannot make Gmail IDs without invitations so we have to search for okay who has the invite and get the invitation for the Gmail ID and we should think that's one of the greatest thing having an email ID and you can communicate using emails you can you can maximum at max you can attach maybe one MB file or two MB file so big more than that you can't attach so but then also we used to write emails whatever it is maybe a formal email informal talks between the two friends whatever it is the email was a very very popular thing and then came the you know some messenger chat messengers like for example you have used to have Google talk I don't know whether you know it or not then you have Yahoo messengers so people used to communicate using that and then now WhatsApp has come WhatsApp has completely eliminated the need of SMS it has 90% of email traffic probably went down because of the WhatsApp itself you can send an entire file video images instantly by using WhatsApp and it is free also on top of it so nobody would like to send SMS nobody would like to send email just for a you know informal this thing so no whatever invention related to communication happens the the world will accept it from both hands and embrace it and your invention will suddenly become hit because it is a basic need we are a social animal we want to communicate okay that is one of the reasons for our existence if I put it bluntly okay so that is a reason why we are studying this chapter communication system I am not talking about a system which Akbar and Birbal has put in I am talking about a modern day system which is of course technical and it is you can say it's a technology chapter just like EM wave it's also technology chapter just like semiconductor okay and these chapters you will always feel that the knowledge is incomplete it is I mean suddenly I'll tell you assume this thing is there okay then unfortunately will not be able to get into the details okay because these are just introduction introduction to communication system that's all imagine the way you have learned probably laws of motion chapter in class ninth okay it is like that only you're learning communication system right now and then you will learn the same topic in much more greater detail when you take you know electronics and communication as your major in your engineering okay right now it is just a basic introduction like you know what all things should be there in a system which is used to communicate from one point to the other point what are the basic problems what are the basic solutions that's all okay is it chapter done in your school no so I'll move forward so first thing is we will be talking about what was the basic this chapter is deleted in your school for board exam it is deleted right have you checked that all of you only because has checked that nobody else okay but we we don't know we don't know whether this will be eliminated from your JEE curriculum okay so we will be going ahead as it is do you know that they have removed laws of motion chapter from class 11th you may not know they have removed first law of motion second law of motion third law of motion can you imagine learning physics without that okay what JEE see they are assuming that you already know since you have studied in class 9th okay so that is a very can say sad thing but then yes they have removed couple of chapters in class 10th also they have they have they have reduced the class 10th curriculum by 30% and you know it is only so less anyways it is not good Rahul Mishra don't think this chapter is in my textbook your textbook was probably old all right write down elements of communication system write down it was not there when I was studying class 12th the chapter was not there in my textbook also and it will be good if it if it is removed because many things you need to assume to study this chapter so I think in the new one only they've removed it because I like there's only 14 chapters in the latest one check latest one how do you know it is latest I check the online textbook also that's just to confirm you don't pay attention pay attention here we never know whether it is included in JEE mains or not so anyway it will take two hours all right pay attention here so we are talking about elements of communication system how will you communicate let's say you have a mobile phone okay and you are communicating with someone at some other part of the city and you are calling them and communicating okay so you have created some sound okay that sound has to be communicated like for example I am communicating with you right I am creating sound all right so sound is there near my mouth this sound is captured by someone some system and this sound is getting transmitted to your system and you are able to hear it is not that you are able to hear my sound directly isn't it it is not that I am shouting from here and you are able to listen to me directly but you are listening to me as if I am talking very near to you that is possible only because of communication system fine so there will be definitely one information source which is like you are the information source fine so write down information source let's take an example of myself I am the information source communicating to you okay over here then this particular thing this will create a message and it will go to the another module which is transmitter okay this is transmitter so in between what happens is you have a message but converted into some sort of electrical signal so whatever I am speaking the sound when it is coming it goes inside the microphone the sound goes in the microphone the microphone converts my sound into an electrical signal maybe voltage fluctuation or the current fluctuation and this voltage and current fluctuation is fed to the transmitter okay now this transmitter will then transmit whatever signal is there message signal further okay it will use a channel there is a channel for example when I am communicating with you the channel is pretty wide for example my voice goes into the transmitter transmitter uses internet connection it is my we can say wire is the channel right now and then in between there will be a wireless transmitter transmission between the router and my laptop there is a wireless channel as well so wired channel then wireless channel then it goes to another server using wire and then goes to your router from there it goes to your laptop by using wireless channel so this is a medium you can say okay so transmitter takes the message signal processes it uses the channel and then it get transmitted to the receiver now receiver is not the person it is some device it is called transmitter and receiver are two devices then you have other person on that side you can call that as user of the information now where is the communication system communication system is this inside the red box this is my communication system transmitter channel and receiver is my communication system okay now things are not very very simple the way it appears there will be noise the channel every channel we you use there will be some noise signal that will get introduced okay and this noise is very tricky to handle fine this is the communication system everybody understood okay now this is the communication system which is under study for today now we are going to study about the communication system when we will be studying it we will be using some terminology to understand it for example when we are learning about the motion of an object we first understand what do we mean by displacement what do you mean by the velocity acceleration angular velocity and things like that okay so similarly when we are learning about the communication system we need to learn about the basic terminology which we can use to understand the communication system okay so one by one we list down all of that write down basic terminology good thing is that this chapter is very theoretical so if you understand everything and remember you will definitely score in the exam okay the first one is transducer any guess is what is transition have you heard of it before have you heard of transducer before what does it do anyone have you heard of transducer yes or no no sir no sir never that is strange Ruchir has heard what it is what you saying Krithika what it is like I don't know what it is but I was using like mics and earphones or something okay okay hmm so a transducer is a device that converts write down it converts it's a good chapter for general knowledge also okay so you will learn many new things so transducer converts one form of energy into another form of energy this is the general transducer okay then over here I'm interested in electrical transducer electrical transducer it converts physical variables like pressure pressure displacement velocity temperature whatever it is okay into corresponding electrical signal output so basically it is it can be used very well as Mike okay so what happens is suppose I am speaking you know when I speak I create a sound so nearby mouth the let's say the particle starts oscillating it's a sound wave okay I'm drawing it like a transverse wave but in reality it is a longitudinal but anyways it shows that there is a wave so there isn't there is a particle oscillation that happens near my mouth and put a mic near my mouth wherever the sound is then the mic will take this pressure variation which is your sound wave is a pressure variation nothing else okay so transducer will create one electrical output corresponding to your sound so this is the sound and corresponding to this sound you have this electrical output you have converted your sound into electrical it may be voltage fluctuation could be voltage could be current could be anything okay and there is one one onto mapping so from here to here it is a unique mapping so any point in time you can convert electrical to back to you can get the sound from electrical if there is a one one onto mapping so one particular sound signature correspond to one particular electrical signature so you can easily take get back the sound also from the same electrical signal which got generated so it will be very very similar okay I hope everybody understood transducer it is probably one of the most important components in the communication system and they are of many varieties you might have seen already that mic the cost of the mic can be as cheap as 30 rupees it can go up to lakhs also okay so the quality of mic it can be improved much much higher okay so yeah different different varieties are there but the basic thing is this only second write down signal you keep hearing about you know signal is weak signal is good and all that signal is nothing but it is the information write down it is the information that is converted into electrical signal sorry electrical form form that is suitable for transmission it can be analog or digital don't worry about what is analog what is digital you know we'll probably have a discussion little later on it but not required as such so this is signal okay so basically the microphone creates a signal this one you can say this is signal okay but then you know you can say this is signal but probably this is not suitable for transmission then you know it is better not to call it as a signal if it requires further processing before the you know my what microphone will do it will convert the sound into electrical form exactly the way it is but then still it may not be suitable for the transmission you may have to increase its frequency do some processing on that then only it is suitable for the transmission so once it becomes suitable transmit then it is called signal okay but then if you're talking about a very short transmission for example your mic is directly connected to your mobile phone and you're recording your voice then processing is not required okay so whatever it is you want to understand right what is the signal next one is noise can anyone try to probably explain what is a noise everyone it's undesirable information does it need to be electrical form when I say noise is it an electrical form or not I think it's just when the signal gets distorted no no I'm asking you it is electrical or a sound itself can be said as a noise so sound itself it is electrical okay so for example let's say you're talking on a mobile phone to some with some and with someone so from background the truck moves fine then the noise of the truck got captured on your mic alright then Mike will convert that that sound of the truck into electrical form also the your mic will not differentiate between sound of the truck and what you are talking so both of them will get converted into some sort of signal and it'll be transmitted to the person when the person it reaches to the person the electrical signal that reaches person has the has the sound of the truck also as an in the electrical form okay so if you have some mechanism probably if you can you know probably create a dampener or you have a very special mic which will not catch the sound coming from one of the directional directional mic suppose you have so you even though the truck is having a lot of sound if your mic doesn't catch is it then it is not a noise fine so noise is electrical in nature and and of course our day-to-day life we will definitely call the sound also as a noise but technically noise is a signal only which is electrical but it is unwanted unwanted signal unwanted signal that tend to disturb the transmission and processing of message there are different different ways in which you can cancel out noise okay so well no need to get into detail of that so okay let me tell you one suppose this is your mobile phone you are speaking from this side the truck is moving it creates a sound sound will get captured over here you can have a microphone over there also which will also capture the sound of your sound of the truck sound of a truck this mic also captures this mic also captures but this mic will capture your sound very clearly this this mic and that mic both the mic will capture the sound of the truck almost similar intensity so you can subtract this wave sorry you can subtract this wave from that signal so noise can be eliminated if you if you can use two mics but then I'm telling you in a very crude manner okay of course there will be some algorithm that will be running wherein you need to also identify that you are not canceling out probably when you're speaking some of the sound is captured over this mic also when you subtract your sound will also get cancelled away so it's a very tricky matter wherein you eliminate the noise okay lot of work is going on in that area then the fourth right down is transmitter a transmitter right down a transmitter processes the incoming signal to make it suitable for transmission okay suppose you you want to basically you know there's a difference between transmitter and a loud speaker there's a big big difference a loud speaker will convert your sound into electrical signal amplify it and then again convert into sound so that is the loud speaker it doesn't processes your signal because it doesn't have to transmit it to the longer distance fine that is a loud speaker transmitter when it receives the electrical signal corresponding to your voice it has to do a lot of processing imagine you are speaking with someone and there is another person who is speaking with someone else and both of you have converted your sound into electrical signal using mic and then you have thrown that in air so that some station will catch it and send it to your wherever it has to go okay now imagine in the air there's so many messages they will undergo interference these messages will interfere with each other and create a lot of problem okay so you need to process it so that you know every message should have an information of every data packet that you throw in the air should have an information of who is sending the data where it should go and on top of it there are a lot of other things that you need to do before it is suitable to be thrown in air like that okay so this is a transmitter we'll be talking about what kind of processing is does in this chapter itself then you have receiver as the name suggests receiver receiver will receive the information from the transmitter and extracts extract the message signal what is the message signal this is a message signal this one this is a message signal after you process it things will change this signal may look like like that you know after you do the processing it will look very weird something like this it will look okay so this is how after processing from the transmitter the same message signal will look like this so receiver will extract this from whatever it has received after processing okay it extracts the message signal from the from the processed signal whatever signal it has received from the transmitter okay signal given by the transmitter anyone has any doubt till now everything is clear for any doubt no doubts okay Raju any doubt KTG KTG no sir no sir Akshit Akshit can't hear you can anyone else hear Akshit no no Akshit you're not audible speak bit loud I changed my mind no doubts no doubts okay fine Raju did you put your photograph of your teets as your DP in the zoom yes sir it's like this for a while such big teets you have no sir this is okay your voice is breaking anyways leave it right down the next technical term is attenuation have you heard of this term attenuation then in calm in computer science you've heard of it okay attenuation is basically loss of the strength of the signal while propagating through the medium okay so this attenuation could happen for for example if let's say you might have seen that Wi-Fi router if it is very far from where you are sitting then you may not be able to catch the Wi-Fi signals because lot of attenuation has happened between you and the wireless transmitter so in between there are walls coming in then lot of metallic objects are there which will absorb every of these kind of objects and substance will come in between you and the wireless transmitter they will keep on absorbing the signal and attenuation will keep on happening so if you go very far from the wireless router the signal will be zero okay that's the reason so you don't want lot of attenuation to happen otherwise the strength will not be good lot of noise will be there right on amplification can anyone tell me what is the definition of amplification just whatever you may you you think it is so by like raising it by some factor what what are you raising the signal that's a very broad thing signal has many things the amplitude amplitude amplitude okay so write down process process to increase the amplitude param is there yeah amplitude of a signal okay this is a process amplification is a process to increase the amplitude of a signal and it is used it is used to compensate attenuation your television has an amplifier without amplifier your television will get a very weak signal you'll not be able to recognize also okay so it's a very important process amplification for every communication range it is the largest distance between source and destination up to which the signal with sufficient strength is there now sufficient strength is a subjective term so that is a range also will be you know like 20 to 30 meters 30 to 50 meters like that they will give you range fine this is the range then one more term you'll keep on hearing is bandwidth do know what is the definition of bandwidth anyone other's a bandwidth is high of course the speed will be higher but anyone has any other definition speed of transmission you know is the speed of light okay but then also you have lesser this thing lesser speed okay why the reason is because of the bandwidth issue and bandwidth is nothing but the frequency range frequency range over which communication happens if frequency range is narrow then your data packets which you send in the space suppose you can use only 1 to 10 hertz okay then first this data packet will go then this data packet will go then that packet data packet will go all the data packets will be using entire spectrum of the frequency but if suppose you have 1 to 10,000 Hertz frequency then first data packet will use 1 to 10 Hertz second data packet will use 11 to 20 Hertz third will use 21 to 30 Hertz so that way multiple data can be transmitted at a single time so automatically your speed will increase fine you don't have to create a queue so this is the bandwidth then you have modulation right down have you heard of modulation in computer science yes it's part of modem what it is what what does it mean modulation modulating means what changing it according to the need maybe okay you don't know they haven't discussed it in computer science so they just discussed modem like which demodulates and demodulates the signal didn't like going to depth about modulation but the definition should be told usually what it is anyways so this is the modulation is when the message signal message signals frequency you increase by superposing superposing a high frequency air waves okay this is called modulation so the frequency of the message when you are speaking when the transducer converts it into a message signal the frequency is very less that is not suitable for transmission there are many reasons we'll come to know later on so you need to increase its frequency before it get transmitted so modulation is that process in which you increase the frequency 11th a lot of technical terms there is one more than that's it write down demodulation any guess is what it should be frequency decreases frequency yeah okay well any any other any other do you think okay I think I understood what you said but your voice are breaking so it is a process of retrieval retrieval of information from the carrier wave okay what is a care what carrier wave did when you superpose a carrier wave the frequency went up then the signal has changed it will look like this I'll show you I've drawn here after putting a carrier wave it looks like this bottom right looks like this this is your modified signal then demodulation is a process to get this from whatever else transmitted fine this is what demodulation is okay the last the last technical term which you should know is a repeater have you heard of repeater in computer sir yes sir what it's like to recapture the signal after a certain distance recapture can be done by your mobile phone also mobile phone captures a signal or not what is a basic function of repeater what does it do that amplifiers the signal again that is amplifier repeater doesn't amplify the signal I just make sure the signal doesn't die out something like that it does it increases the range it increases the range of the suppose your Wi-Fi it is there in the drawing room it is not able to reach to one of the bedrooms you can have a repeater in between which will capture the signal and retransmit it okay so a repeater is a combination of receiver and transmitter both it has both receiver as well as transmitter because it has to first receive and then transmit it back okay so it is a combination of combination of receiver and transmitter to be used to increase the range okay so these are all the technical terms I'll just show you the one of the examples you you gave a very small example of the repeater I am telling you in reality repeater is used everywhere have you seen you know a tower on a mountain have you ever seen a tower on a mountain okay have you seen a mountain tower on a mountain no okay so typically you know a repeater is placed on top of the mountain you want the height of a repeater to be bigger then it is used in a best way this is a repeater let's say you have a tower let's say here this is a tower and here is another tower now because of the curvature of the earth this tower cannot interact with that tower in between earth is coming you can see this fine so what you can do is you can use a repeater you can communicate with this and this will take the message and transmit it here so you have increased the range earlier you were not able to reach to this tower now you're able to reach it by using a repeater okay so it's not only for the Wi-Fi let me draw the tower nicely satellite you know different frequencies satellite operates if you have a satellite you don't need repeater okay I'm talking about the different kind of communication where you are using the you can say a ground wave or satellite has a different set of frequency just understand that and you can you know using transmitter and receiver as in repeater you can increase the range quite a bit suppose you have such big big antennas on top of the mountain you can effectively communicate anywhere on the earth okay you can communicate like that okay now what Richard said you can use the satellite also yes you can use it why not even satellite you can say it is kind of you know repeater itself if you are using it like that okay so this is one of the common example of the repeater fine now I think I should have discussed it at the start I have shared a set of result that these guys got your one-year senior have you noticed any anything anything to highlight there have you noticed that anything the second good do you do you know how much time they got in the second attempt do you have idea because of the covid the second attempt happened in the September end so how much time they got after the board exam got over to can you count it and tell me quickly six months six month of nothing else but preparation of J mains nothing else they don't have anything to worry but then also second attempt their percentile went down do you know their scores went up most of their scores went up by 20 marks 23 marks like that but the percentile fell the reason everybody else was better prepared okay because they don't many of them they don't care much about the board exam so when you prepare for a board exam they will also be preparing for J mains only and it is sad to say but then yes it is difficult to match the kind of hard work they are doing you know they will be giving everything they have they'll be working day and day out sometime they forget that they have to sleep they'll just keep on solving question and then from night sunlight comes this is night out usually that that is what they do and that's the reason why I say that for Bangalore kids you should not you should never never ever count on your second attempt okay first attempt is your best chance because everybody else also will be like waking up only that oh it is a first attempt we have one more attempt like that they'll be taking it lightly all of them second attempt they'll give everything they have because they you know that is the last chance they have so better to strike when everybody else is not very serious fine so and then you have seen I have shared 14 people's percentile okay out of those 14 people only two of them increased and their increase in percentile is just 0.14 or 0.2 percentile like that it was not a big recovery and almost everyone's percentile fell everyone including Bharat Sukirt everyone's percentile fell okay so understand that your first attempt is everything you have second attempt no matter how well prepared you are you bound to get lower percentile okay give you a best shot in the first anyways so this is these are the technical terms now we'll be discussing few things for example let's talk about the bandwidth so is there anything that decreases the amplitude of this like amplification attenuation okay amplification is to compensate attenuation right that's the okay bandwidth bandwidth of signals see we will be using digital signals to communicate most of the time okay it will create a square waveform all right and when you're using the multiple multiple signals let's say you're using sinusoidal signals all right then if multiple multiple frequencies they're superpose they're going to create a square wave sort of thing I'll just give you one example let's say this is there is a square wave let's say this is a wave okay now let's say I mark these points zero zero point five and one okay if I have a frequency which is this on to this let's say this frequency is mu naught on to this if I add two mu naught frequency two mu naught frequency how does it look like it will look like this mu naught frequency with the same amplitude will look like this all of you understand this yeah how it look like and when it's superpose if it's superpose then it will look like that let me use the red one once it gets superposed both the frequencies you can just add graphically you will see that you'll get this kind of thing okay on top of it if you add three mu naught okay then you're going to get this kind of thing so you'll see that if I keep on adding higher and higher frequency it is becoming closer to the square wave only fine so basically a square wave can be thought of a collection of multiple frequencies higher frequency higher frequency contribution do you think it is lesser or higher higher frequency contribution to the square wave formation what do you think the contribution of three mu naught in the shape of a square wave is higher than mu naught or lesser than mu naught higher kase ho gya less than enough the shape no no no the shape is pretty well defined by the white line itself the the two mu naught has refined it only then three mu naught has further refined it but the shape was defined by the white line itself do you all agree so contribution of higher frequency is lesser higher frequency contribution is lesser okay so that's the reason why if you are transmitting a square wave in a digital form then we need higher bandwidth we need higher bandwidth so that we don't lose out on the message because you know from mu naught to two mu naught anyway there is no frequency between mu naught and two mu naught that will give a square wave so if I if I transmit a square wave they will be able to extract mu naught two mu naught three mu naught four mu naught like that okay but my bandwidth is just zero to let's say hundred Hertz my mu naught is let's say let's say 50 then I'll have 50 and 100 only two frequencies I can have if I use a square wave like this okay but if I have zero to thousand Hertz then I can have 50 100 150 200 250 300 I can have multiple frequencies to play with okay so that is one simple reason why having a bigger bandwidth is a desired way to increase the communication a better manner okay now talking about the bandwidth of the signals there there is this international telecommunication union which has defined for what purpose what should be the range of frequency that you should use okay you cannot randomly say that okay fine I'll use gamma rays for my radio communication all right it will disrupt everything and if you do that it will be illegal fine so that is a reason why there is a very very well defined standard that everybody has to follow and you know there is also bidding that used to happen for example the government decides that let's say between 10 kilo Hertz to 200 kilo Hertz this frequency will be used for communication so probably Airtel and Vodafone will come and say that Airtel will say that I will take bandwidth of 10 kilo Hertz to 60 kilo Hertz and I'll be paying this much okay then Vodafone will bid for another set of bandwidth so like this you know it is a very well regulated thing wherein you have to pay money to the government also to use a particular bandwidth spectrum sale yes and that is where the all the corruption you have heard have you heard of 2g 2g scam 2g scam anyways that is what it is Raul Mishra mute yourself write down so there is this uh union it is called the international telecommunication union write down the short form is itu so I'll just list down the set of frequencies that are used for various purposes you don't need to mug it up it is just for your information sake okay am broadcast have you heard of am broadcast yes have you heard of all in the radio no yes right so am broadcast is that okay and all in the radio runs on it it can travel to very very far distances okay so the frequency for that is 540 to 1600 kilo Hertz okay can you quickly calculate the wavelength for 600 600 kilo Hertz frequency how much is the wavelength the 500 what 500 meters 500 meters all of you so you can imagine how big the wavelength is typically or an em wave because the speed is very high okay and just so that you know that the size of the antenna size of the antenna is close to lambda by 4 if suppose you're having a certain frequency that you're using the antenna used to catch that signal should have a size of lambda by 4 roughly because the natural frequency of the structure has to match with the frequency of the this thing so that's that is where all that calculation coming and roughly lambda by 4 should be the size of the antenna so imagine 125 meters size of the antenna okay it will be a huge huge antenna so it is practically impossible to have this much size so that is one of the reasons why the message signals frequency is increased by doing modulation you modulate it increase its frequency okay fine and that is the reason why we do that so that the wavelength decreases and the size of the antenna requirement goes down otherwise the kind of frequencies you are using for mobile communication if modulation is not done you will require a size of let's say 10 to 20 meters big antenna should be there in every mobile phone so you can imagine your antenna of mobile phone in order to carry that you need a track fine so that is one of the primary reasons why we need to increase the frequency using the modulation so anyways next is FM broadcast have you heard of FM yes do you guys use FM like you guys listen to it it's only in the car so you receive the modulator would have no no no not not that yeah once you capture it it is then you can process it you don't need an antenna to process it then okay yeah so so anyways so FM broadcast frequency is roughly 88 208 megahertz now whose bandwidth is higher AM or FM whose bandwidth is higher FM not AM okay there is 10 is power six here this is 10 is power three kilo is 10 is power three okay FM is higher fine next is television television typically usage is 54 to 890 megahertz have you seen cordless phone by the way cordless phone yes so I have it still have you have it okay yes okay so you know cordless phone the frequency it uses is close to AM broadcast frequency so if you use cordless phone you can try it if you have a radio that old radio if you have it I don't know whether you have it this old radio if you can rotate the knob probably on your any digital radio also it will be fine if you rotate the knob you're using the cordless phone it is emitting signals it will it is receiving and transmitting so your radio will be able to catch the signal of the cordless phone because the frequency is matching here and whatever you're talking whatever you are receiving everything can be heard using a radio okay so it can be easily intercepted very very easy it is so cordless phone if it is a secret talk it should avoid anyways next is cellular mobile phone cellular mobile frequency is 896 to 935 megahertz typical typical frequency range okay so you can see that cellular mobile phone is safer none of the other instruments will be tuned to catch this much frequency then you have satellite communication have you seen in the war movies the sometimes soldiers will be carrying on their back a big antenna device and they will try to catch a signal have you seen something like that on the war movies right that they are trying to do satellite communication they will first have communication with the satellite and then satellite will connect them to whatever this thing that happens at that happens at 5.9 around to roughly 6.4 gigahertz very high frequency fine so these are the ranges and everybody has agreed that this is what is the appropriate range okay and yes sometime people debate that you know that a lot of cellular tower should not be there where the intensity of the cellular towers frequency should not be very high because it is harmful for the humans so a lot of research is going on people are debating whether it is harmful or not people are also debating whether the wi-fi signal that is there inside your house whether that is harmful for humans especially for the kids okay so they say that always you can put your mobile phone on the flight mode when you are sleeping don't put it near your head all that thing is very much prevalent for the health reasons otherwise it can create health hazards people say that it can slowly and slowly it can develop tumor in your brain also if you put it near your head continuously for so many years and that is the reason why you know although still people are debating on it but I would say that you can play safer always put your mobile phone in a flight mode because near the antenna of your mobile phone the signal will have the highest strength okay it is trying to catch it anyways so this is the brief discussion on the technical terms bandwidth of signals and which bandwidth to use when fine so so what is the full form of AM and FF