foreign yes Okay so okay so as I was saying that thermodynamics so many systems we have to manage all together to take a class and it's so much confusion anyway so what I was saying is thermodynamics I think you have you may have already heard this you know uh bifurcation or definition that thermodynamics is made up of two words Thermo and Dynamics Thermo is basically what what do you mean by Thermo or thermal can anyone tell me quickly you have to be very responsive okay yes very nice Thermo means heat what is the dynamic spins Dynamics means motion yes motion if something is in motion you can say it's Dynamic okay so basically when heat is causing the motion motion of what motion of atoms or molecules so we can if we are studying the motion that is caused by heat that is study we do it in thermodynamics so it's simple word if heat or energy is causing emotion a motion of what atoms or molecules so if motion is happening then what will happen its pressure will change atoms okay its pressure will change its velocity will change its temperature will change okay another properties may also its energy will change internal energy will change entropy will change everything like Well Properties will change and we study that how these properties are changing okay due to heat transfer energy transfer so that study we say that it is Thermo Dynamics okay so what is the scope to study where motion of the atoms and molecules of a substance is caused by heat or energy so here basically it is a branch of science which deals with energy conserve a conversion and its effects on physical properties what is this this is physical properties what is the pressure what is the temperature these are all physical properties okay so here we deal with energy conversion how the energy is converting and what is the effects it is causing on the properties of the substances this is what we do study in thermodynamics okay now what is the ultimate aim what do you want from thermodynamics okay TK whatever is happening with prop ER pressure is changing volume uh volume is changing velocities changing temperature is changing whatever is happening it's fine but why do we need to understand it why we have to study the whole subject to understand how these things are happening so the whole objective the ultimate aim is to basically understand when this conversion is happening then how we can make an effective conversion basically how to effectively convert one form of energy to another form so that we can so whenever one form of energy is converted from to another form okay we can utilize this energy in some form we can convert it into work we can convert into electrical energy okay we can convert into velocity or potential energy so basically the aim is what how to convert this in an effective way when we are converting one form to another how to do it in a very effective way okay with minimum entropy with minimum losses in a very reversible way so how to reduce irreversibility that is the ultimate aim of the thermodynamics all these things we are going to discuss do not worry okay now there are basic definitions what are the basic definitions so first of all is a system now what is a system basically anything around you over which we are going to you know do I study or we are going to focus on something that is our system for example you have your I mean you know like people say system but still we have a very vague idea about what a system is so I will tell you one thing for example you have a power plant so you have a heat exchanger here you have a compressor here let's show a turbine let's say here you have another heat exchanger here okay then a pump here let's say okay turbine heat exchanger so at a particular time we are only going to focus on one system for example we are only focusing on this heat exchanger what is happening in this if Hot fluid is entering cold fluid is also entering what fluid is coming out whatever is happening but we are focusing on this so our focus is on this he's that heat exchanger and then this is our system this is our system we can also take we can also take more than one system for example we can take this system now we have two systems here so whatever is entering here whatever is coming out but we are going to treat it as a black box and this is our system we can take three systems as well we can take all of them we can take them as a whole system although then it will be a cycle but still we can treat it in our system okay so system is something that we are focusing on which we are going to study how the properties inside the system is changing is basically our system the r Focus whatever is our Focus that is our system and it's very important to determine what is your system because you know a lot many problems you will face that there are so many unknowns and you are not able to solve them why because you did not decide your system properly okay so you have to see what is the if you are if you want to solve a problem you have to see what system to choose okay that we are going to see when we solve you know a few questions or we can uh see that one second okay so this will be our system anything outside the system now let us say this is my heat exchanger and I have chosen it as my system now anything external to this is surrounding and this system and surrounding is separated by something that is called as boundary now this boundary can be real or imaginary it can be real or imaginary okay here we can see a real boundary but it could be for example there is a very long pipe very very long pipe so you cannot pursue a study on this whole pipe so what will you do you will imagine a imaginary boundary like this and then you will see how the fluid is entering at what pressure at what velocity and at what entering entering at what pressure it is exiting at what velocity it is everything and you perform your analysis so in this particular time we have imaginary boundary okay we have imaginary boundary boundary so boundary can be real or imaginary and everything system surrounding boundary everything constitute is called as universe is it clear yes or no quickly tell me okay very nice so very important things about boundary so it is a surface through base system and surrounding interact so basically boundary is the separation between system and surrounding and this is how so if yes yes boundary we are anyway discussing you see this is this here we have focus on Boundary only okay so basically if this is my system [Music] foreign they are separated by a boundary now if system and surrounding have to interact with each other then how are they going to interact they have to interact through the boundary so for example heat transfer we are going to see heat transfer is happening from the system to the surrounding that means both system and surrounding are involved so this heat transfer has to cross the boundary if heat trans ferred the system itself it is not interacting with the surrounding okay so in order to in order for the system and surrounding to interact that thing must cross the boundary it should go through the boundary if something is happening inside in the you know surrounding heat transfer is happening outside from one body to another it does not it does not matter you cannot say we are not going to focus on this we are not going to focus on this we are only going to focus what heat transfer is crossing the boundary that's all okay just one second okay so this this much is clear Amit first of all then we will discuss more about boundary yes no Amit anyway so as I told you earlier boundary can be real or imaginary I have showed you example as well okay this is a real boundary this is a real boundary and this is the imaginary boundary okay now next thing is about real boundaries shown by continuous line and imaginary boundaries shown by share first slide what slide this one this one you will get all the slides anyway don't worry about it I mean are you trying to write it with me don't try to write anything okay just try to understand what I am saying and you will get the ppts what I am writing also you will get with the PPT whatever is written on the PPT you will get that whatever I am writing also you will get that okay so focus on what I am saying not because if you try to write everything then I cannot cover much okay so don't try to write if you if I am saying something and you think it is important or you will forget it maybe just try to write that okay so as I showed you it can be real or imaginary now real boundary is shown by continuous line you see this is a continuous line an imaginary boundary is shown by dotted line what else now boundary can be fixed or movable boundary can be fixed or movable what do you mean by this for example you have a pressure vessel pressure pressure vessel okay like this now it has a fixed boundary it is not going to move okay like a solid cylinder or something it sticks boundary so this is called as fixed it is not going to change but what is mobile boundary for example you have this you have a reciprocating cylinder and you have walls valves here so when fluid is going to come inside this and let me show the boundary also for example right now this is the boundary okay now when fluid will flow inside this piston is going to move in this direction so the boundary is going to change boundary is going to expand like this and when fluid is going to come out then piston will move in this direction the boundary make reduce okay so this is called as flexible boundary or movable boundary movable or flexible okay is it clear yes what do you Shivam what what fixed Moi value you want me to repeat it's very simple only you see look if you take a piston surrender and there are more walls in it there are no walls then what is the boundary boundary is this this boundary is not going to change okay it is fixed but if you have a piston cylinder with a valve wall means fluid can come out fluid can go in and this is your piston and right now this is your boundary this time this is your boundary but let's say fluid is coming in so this piston is going to move ahead forward so you see this line this line is going to change this one is going to change so boundary is increased if fluid is coming out then piston is going to move in opposite direction so this boundary is going to reduce so this you see green line is moving in this direction earlier it was moving in forward Direction so now boundary is changing so this is called as flexible boundary okay hello let's move ahead now the systems can be classified as closed open and isolated but in what terms how how are we classify okay if we are classifying something it should be on some basis what is the basis as I told you that this system can interact with surrounding but how is it interacting it can only interact in two ways first and I told you one thing already if I am saying these two things are interacting that means that thing should cross the boundary so mean if any mass is entering or any mass is leaving Mass out or in so where it is coming from it is coming from surrounding it is coming from surrounding and entering into the system it is crossing this boundary you see it is crossing this boundary similarly it is coming out from system and going to surrounding so this is called as mass interaction the another type of interaction is energy interaction you see energy when energy comes in from the surrounding to the system and when energy goes out from the system to the surrounding so again it is crossing the boundary you see it is causing the boundary that means a system and a surrounding can interact only by two ways mass and energy so either Mass transfer an energy transfer and why do we say transfer because it is going it is moving from one place to another that is why we say transfer we do not say just Mass because mass in itself is nothing okay it is if if the system and surrounding has to interact if some mass is sitting inside the system then it is internal Mass it is not interacting with the surrounding for the interaction to happen it should get it should transfer from the system to the surrounding that is why we say Mass transfer energy transfer now based upon this interaction our system is classified on closed open and isolated system okay now what is closed system [Music] closed system is basically when you see if this is your system and this system will not allow it will not allow any Mass transfer must know how can I say Mass transfer is equals to zero no Mass transfer can happen this boundary is not going to allow any Mass transfer what can you select for example you have a Pistons random like this okay now it has no walls let us say it has no walls if there are okay sorry we have a piston cylinder Arrangement and it has no walls some masses they are already okay here we have some Mass inside the system now let us let us Heat this okay let us give some heat or you know provide some heat now why how are you hitting it you are putting a fire or something whatever it is happening now because of this heat you are heating on other side okay this is surrounding part you are give you are you have lit a fire and because of this fire heat will get transferred from the system to the surrounding but there are no wolves here so because there are no walls you cannot transfer Mass here because of this heat this Mass will heat up its volume is going to increase and this piston is going to move forward or if you are taking heat out of the system for example you have you have installed a heat exchanger here both sides and this heat exchangers are taking out heat from here okay so volume will decrease and piston will go in so basically what I am trying to tell you is it is a system that is not allowing any Mass transfer what it is alloying it is allowing only energy transfer two type of transfer can happen energy trans but closed system can only allow energy transfer no Mass transfer is allowed no Mass transfer that means if no mass is entering or leaving that means it is a fixed Mass system it is a because whatever system has mass it is fixed no mass is entering no mass is leaving okay this is a fixed Mass system and also it is called as no flow non non-flow system non-flow system okay so these are the things that is same thing is written here mass of the system remains same but the volume you see volume is changing because energy is because heat is non-flow flow basically if mass is Flowing then you can say flow process it is don't go about process here let's say system as of now when we understand process then we will go to process let's say system okay it is a non flow system and non-flow we are saying in terms of mass because mass is not flowing that's why no non-flow if mass will be flowing it will be a flow system okay so same thing I have told you okay the important Point here to note is the first point is there is no Mass transfer second point is only energy transfer and the third point is it is called as fixed mass or non-flow system okay now adiabatic boundary is basically not allowing any heat transfer adiabatic is what no heat transfer so you see energy also we are going to see later on energy is also get transferred in terms of heat and work so we are going to see later on now if this boundary is adiabatic then only work transfer will happen no heat transfer and rigid boundary Matlab no work transfer as well okay although it's not very frequently used it is it is not very frequently used adiabatic is very frequently used adiabatting Matlab no heat transfer adiabatic means no heat transfer you remember this it bound basically we have insulated this boundary we have provided a very strong insulation here so now it is not allowing any heat transfer also it is not letting the heat to go inside okay now next is open system what is open system simple open system means whatever restriction we had now we have let's say piston cylinder arrangement and we have walls here okay so adiabatic is closed or isolated no I am talking about boundary boundary is adiabatic okay isolated means we will talk about isolated though wait two minutes we'll talk about isolated okay adiabatic simply means no heat transfer nothing else okay it could be adiabatic flow system can also be there okay so adiabatic you just remember you don't confuse adiabatic with close or isolated adiabatic simply means no heat transfer everything else can happen work transfer can happen Mass transfer can happen everything can happen okay now if we have this kind of system and we have put a fire also here you see I have put a fire also here at the center and fire also output now what is happening and this is my system it has some mass of system as well okay now what is happening some mass is coming in the mass is coming in and some Mass could be going out as well now based upon how much mass is coming in how much mass is going going out this mass of system is going to increase or decrease for example 10 kg per second is coming in mass in is 10 kg Mass out is 20 kg per second that means going out is more so this mass of system is going to reduce okay it's simple the case of your bucket you know like uh your drum water drum or bucket for example in that drum you have already 50 liters of water let me let me say it in terms of kg otherwise again you will get confused 50 kg of water I am saying I I know it is not correct but because we say water in terms of liters but anyway 50 kg of something okay now you see 20 10 kg is coming 20 is going out so what will happen this 50 is going to reduce because more is going out the mass of system is going to reduce similarly vice versa if more is coming in less is going out then mass of system is going to increase so it is allowing the mass transfer first of all it is allowing the mass interaction also heat will go in so energy interaction is also happening energy as well as mass interaction and because Mass interaction is happening it is called as flow system okay and here we basically focus on definite volume or control surface and for and actually most of your power plant systems for example heat exchangers you know compressors another heat exchanger turbine they are all what flow system because you see mass is going out from this heat exchanger and entering into the compressor when it is coming out of compressor it is going into turbine so mass is continuously entering continually going out so they are all open system most of your power plant equipments are open system because mass flow rate happens there okay boiler condenser turbine and Arrangement piston cylinder arrangement with walls okay next is so open system as I said is TD flow and there are two types of open systems is TD flow on STD flow what do you mean by Steady flow STD flow means it simply means mass of the system with respect to time is equal to zero there is no mass of the system is not changing similarly let me say Delta M and similarly energy of the system is not changing with respect to time so what does it mean for example mass of system is there and mass is coming in and mass is going out now in steady flow system this mass in will be equal to mass out it is a compulsory condition for steady flow and if entire Engineers I mean reciprocating engine if you say it is a open system because you see air comes in fuel comes in all that thing mixture comes in they're all open systems okay so steadia flow systems are it is a necessary condition so mass in is equals to mass out and if Mass n is equals to mass out there that means this Mass inside the system with respect to time it is not going to change so it will be equal to zero it will be equal to 0 okay so there is no Mass change of the system ma Mass inside the system is constant simply what about an STD flow an STD flow means mass of system is there mass in and mass out now it's honestly means Mass DOT in is not equals to mass flow rate out if they are not equal what will happen for example more mass is coming in less for example ma m dot in is less then m dot out so it is come less is entering more is going out so what will happen mass of system will decrease okay if mass flow rate in if coming in is more than what will happen mass of system will increase that means your mass of system is not equal to 0 with respect to time it is changing Mass is changing with time and here Mass is constant with time okay this is your STD this is your honestly tell me variable is it clear okay very nice also I would ask you to uh can you tell me have you studied thermodynamics before very quickly like are you reading are you studying everything the first time or you have already done it okay I think most of people have already first time was not I mean I know you would have studied in college but I know how you study in college uh so okay Ravi Teja is first time already done it Amit very nice yeah I know how you do in college so I would not I mean I would not expect much if you are saying about college but for gate or for any other exam if you have done it then I would be very happy suryans is first time okay anyway so it's my really humble request to all the people who are doing it the first time no sir in college only okay sonali it's okay so College people who have done it in college I really don't expect I guess yesterday forget okay so I really don't expect much because I know how you study in college you just study like two three days and just you know okay let me pass and all I have to study six more subjects but basically if you are studying for gate you need to be focused and I would request everyone to at least give it a read okay take any notes whatever it because you see it is a very brief sessions okay so I will try to cover everything but I cannot go slow okay so if you ask me to repeat one perfect again and again it will be really difficult content wise to cover those content okay so I have to discuss that time okay so basically I will be going to cover everything but I would also expect you to study have some little idea about what we are going to study and you know little idea about thermodynamics so that we can quickly move over other topics also what actually happens is when you ask a small small doubts no like when you ask me to repeat this again repeat that again and if it is a complicated topic like entropy or something or you know um something like really complicates it's really fine you can ask me three times repeat but if it is simple topic and you are asking me to repeat so what you are doing is you are wasting time that we can utilize in complex topics to study you know to give it more time so it's basically your loss only because I already know those topics so I would not be able to stand spend more time in those topics okay so please pay extra attention please try to figure out questions that you want to uh you know like just try to be focused on if you are focused on what I am saying I think most most of the doubt will be will already be cleared okay but anyway you are always you know open to ask sir please repeat I just expect you to for to be more focused and try to read more okay so let's move on let's move further isolated is simply simply means look these things are never they never asked an exam okay it's like very rare they asked they are very small small Concepts so let's move at very quickly so closed system was no Mass transfer only energy transfer open system pass both Mass transfer and energy transfer what about isolated system no Mass transfer no energy transfer simply space [Music] you have to be uh you know follow something more specific I need to check usually I tell for mechanical people okay but for you know because too much content if you start studying pknock then you should you will waste a lot of time although it's a very good book okay Central is good I mean but Central is good for concept point of view you know like uh if you want to actually understand thermodynamics so like Theory wise if you for I would re I would suggest Central to someone for example you are stuck at a topic you will start start at uh you want to know the physical significance of something then I would say you go and study that particular topic from that Central Shapiro is good yeah is actually a good book for Aerospace I think that is recommended yes okay so so basically for example you have a thermo flask you you know these uh thermal voters that you buy from what is the famous brand uh uh it is a very famous brand new I don't remember okay uh so what Milton yes very nice Milton yes so you you see these bottles and you fill up water okay so once you have filled up the water and you close it once you okay you have opened it and filled it okay that's fine but once you have filled it now water is there so now no water is going out of the system and also no heat is you see normally it will get for example you have uh you have filled it with hot water so now it will take around 10 hours to go from 50 degree Celsius to the surrounding temperature of 25 degree celsius why 20 why why it is in 10 hours or or eight hours why because you see energy transfer is happening but it is significantly less it is very very very very less so you can say basically in rough terms that no energy energy transfer is happening okay so this can be considered as isolated system or example your Universe you see this is your universe and that is why we say energy of the universe is conserved because you see nothing goes out of system is also here surrounding is also here everything is inside the system inside the universe so nothing goes out no Mass goes out of system no energy goes out of system and that is why say universe is isolated system okay so basically this is a closed system with no energy interaction so closed system what is Blue System no Mass transfer if there is also no energy transferred closed system it will be isolated system Okay so now very important terminology in thermodynamics very important everything we are going to discuss these terms will come again and again and again okay let's start with this just one second give me one second okay so there are these five things that we are going to discuss you know this terminology will come so many times what is what is the property how the properties the only what is the state of system thermodynamic path process and cycle so what are these what are these let us discuss them one by one first let let's just go to property what is the property property is you see how how do if I if I want to describe you how would I describe you for example you know like uh what is your height what is your weight what is your uh you know like uh what is your qualification so basically it's the characteristics it is the how how if I want to define something yes characteristics okay so if I want to define something I will Define it by characteristic of that thing and if I have a system I have already told you what is my system for example I have a heat exchanger okay so or a compressor or a turbine so what is the pressure in this system what is the temperature what is the volume so these are characteristics now it can be identified observed characteristic that depends upon the state of system okay so based upon what you are giving how much energy you are giving how much mass is entering so these characteristic characteristics are going to depend on that and it can be measurable for example pressure volume and temperature and unmeasurable like enthalpy and integral energy now so many times you will see that when people tease thermodynamics they will always say what is the property it is the measurable characteristic of the measurement of the system of the system measurable characteristics of the system it's not necessary it could be measurable you cannot measure enthalpy you see you cannot install a system here or you know like a device and you can measure enthalpy it's not possible you cannot measure internal energy of the system there is no device that can measure internal energy okay but there are properties okay so it can be measurable it can be non-measurable now then how do you measure how how do you define these basically you define these unmeasurable properties in terms of measurable for example enthalpy is defined as U plus PV and what is u u is equals to m c t now temperature is measurable so U is equals to m c t you can measure temperature that's how you can Define this unmeasurable quantity now similarly you can measure this by you can measure pressure right you can measure volume pressure gauges you have okay and temperature or thermometer you have so you define these unmeasurable quantities in terms of measurable quantities so that you want to give it a value but they are all properties so property can be measurable can be unmeasurable now there are two types of properties extensive and intensive okay now what is the extensive property extensive property is a property which depends upon the mass or extent of a system mass or extent of a system okay now what do you mean by mass or extend extend means size okay so you see if I increase the mass of the system then if the property is changing then it is a extensive property if there is no effect on the property then it is intensive property okay it is extensive is basically it is dependent on mass or size for example mass volume internal energy you see internal energy how do you find internal energy m c t so it is dependent on mass how do you define enthalpy enthalpy is defined as U plus PV what is u m c t what is p we will see idle gas equation PV is equals to MRT so m r t so basically it is also dependent on Mass c t plus m r it is also dependent on mass similarly entropy is also dependent on Mass okay so these are all properties they are dependent on Mass what about intensive property though intensive or basically they are not dependent on the mass they are independent of mass or extent of the system and also two extensive properties is a intensive property so for example you see what is extensive property you see mass is an extensive property okay what is volume volume extensive or intensive property extensive so if I divide this mass by volume what do I have I have density and density is basically a intensive property yes so numerator is extensive denominator is extensive so ratio of two extensive properties is intensive also you can take it in a way that if you have you see what is capital h capital H is m c or let me tell this in terms of internal energy U capital u by Mass is equals to m c t by mass and mass and mass get canceled c t so now this is independent of mass and this is called as small U or specific internal energy so this is also you see this is extensive property this is also extensive property ratio of two extensive properties is intensive property got it so you can either say this or you can also say specific extensive property is intensive property so this is the example of specific so this is specific internal energy and this is intensive property specific X so you see when I this is extensive property right this is extensive property now so I can say internal energy now if I say is specific extensive energy if I say specific internal energy so what is this small U is equals to Capital U by m and this is intensive property okay specific means per unit Mass yes that is that is a general definition if you define if you divide something by mass you call it specific for example Capital H to divide it Mass specific enthalpy entropy divided by mass specific entropy okay so specific means per unit Mass yes that is true what it there is but there is just one exception to it that is you if you divide Q by m it is not called as specific heat specific heat is CP okay so Q divided by m is basically you say Q Dash or something okay one exception to this rule otherwise specific means per unit Mass clear yes or no quickly tell me okay so you can see this for example you can take a system you have this one system and here you see pressure is p temperature is T volume is V now let me take one more system here here also pressure is same temperature is same volume is same for example if this is tan this is 20 and this is 5 so this is also 10 this is 20 and this is 5. okay units I am not saying for example this is in kilo Pascal this is in kelvin this is in meter cube whatever units you want to assume okay now this volume okay not velocity volume now let me remove this barrier from here so if I remove this barrier it is a you know removable barrier so let me remove this barrier so if I remove this barrier tell me what is the pressure of this system now quickly tell me is it P it is 2p it is p by 2 yes it is 10 that means p what is the temperature temperature will be S 20 what is volume just one second someone was asking something yeah volume is 10. so basically volume has doubled to V okay someone was asking something one second who was asking okay just wait I'll explain I'll explain okay so that means you see mass is increased here mass is become doubled here if it is Mass and here it is M now it is become 2 m okay so because of this mass or the size pressure has no effect pressure has no effect on it temperature also remains same but the volume has changed so that is why we say these are intensive properties these are extensive properties extensive property is intensive property it's simple you see H is equals to m not then I have to write the whole formula let me write okay let me write X only h c p t P it is also like how I can write this h now you see this is a this depends on M now if I divide this thing by m this is also I divide by m so what is the final expression you will have c p into t now is there any Mass term in it for example for example your mass is 10 kg your mass is 10 kg and you have to calculate h so if you want to calculate H for example CP is 4.18 and let me write 4 only okay let me write 4 only CP is 4 and temperature is 100 okay and I want to calculate h when mass is equals to 10 kg why let me calculate small H small H is CP into T that means 4 into 100 is equals to 400 now let me increase mass by 20 kg so let me calculate cap small H again CP into T 4 into 100 is equals to 400 is my exchanging small h it's not changing that's I mean once you divided by mass that means it is become per unit Mass here everywhere my Mass is equals to 1 kg simple tonight but you see Capital H will change so Capital H here will be 10 into 4 into 100 then again it will be 20 into 4 into 100 okay it is going to change what is it no for did you not understand or not change tell me okay you tell me yes or no if you understood the concept yes or no okay I understood understood okay you want me to explain again what I mean I have explained using two methods and I really cannot make it more simpler but just for your sake I'll explain it one more time look extensive property in the same volume container if we add more gas then density will not density increase like in LPG cylinder same volume but you have to increase the volume as well you see density is equals to mass per unit volume so if you are changing Mass so it is going to compensate volume is going to compensate for it okay for example if this is the container and first mass is basically let's say 10 and volume is what 5. okay so if you increase the mass what will happen volume will decrease volume of mass changes as you use it I mean basically here volume will remain fixed but basically for density U if one if the mass is changing then volume will automatically adjust itself so that density will not change okay density is what density mass per unit volume okay the number of atoms per unit volume per unit volume volume is one it is one meter cube how much mass can you accumulate in one meter cube is density simple volume you will take one meter cube okay now coming to bhagyashree how can I explain you one more time okay let's see oh okay I'm running out of this ticket look H is equals to m c p t now Mass is equals to 10 kg and mass is equals to 20 kg okay so if I calculate mass it will be 10 and let me take c p is equals to 4 Joule per kg Kelvin and temperature is equals to 400. 100 let's say so if I want to calculate capital H now you see it is dependent on mass okay so I can say 10 into 4 into 100 so whatever it will come I it does not matter then H1 H2 20 into 4 into 100 okay now what is small H it is specific enthalpy that means Capital H divided by m so m c p t by m so M and M will get canceled so it will be 1 into c p into T Now everywhere mass will remain 1 kg only mass is not changing okay enthal specific enthalpy is calculated Always by taking as mass is equals to one you take whatever Mass you want in your system it does not matter specific enthal P will remain same if you are not changing temperature okay so now if you want to calculate H1 is equals to 1 into 4 into 100 and H2 is equals to 1 into 4 into 100 so it will remain same only okay so for all the specific quantities you take per unit mass per unit Mass means simple it is one kg Mass it does not matter you always take 1 kg okay is it clear we have to quickly move on but obviously quickly tell me is it clear if it is not clear then once you saw you know like you will start using this it will come into your habit okay we are actually running out of time 2148 has already happened only one R is left okay and I think we have not even covered half of it thermodynamic state state means what when so I have told you what properties pressure volume temperature and all once you fixed I fixed you know when you are when you fix the values of the property yes yes which temperature and pressure will increase yes of course it will you see PV is equals to nrt MRT p is equals to density RT so if pressure is density is equals to P upon RT okay if pressure is increasing density is going to increase if temperature is increasing density is going to decrease okay we will discuss they don't worry about it don't you know like let's focus on where we are okay state so basically if you fix the value of properties for example I have fixed pressure is equals to 10 kilo Pascal and volume is equals to 5 meter cube so what will I do let me fix 10 kilopascal here and I have fixed 5 meter cube here and if I come to a point this is my state of system so for in order to define the state of system you should have definite values of the properties when the properties of system have definite values at a particular time the system is said to be exist in a definitive state so basically on you see if you are giving Heat its temperature is let's say 30 degree celsius if you are continuously giving heat its temperature is going to change 31 30 to 33 so you cannot fix it okay so basically you have at a particular time only let's say you have defined 30 degree Celsius is fixed and pressure is one kilo Pascal is fixed this is your one condition so this is your one state of system then let me explain it in this way you have a system pull initial pressure is one kilo Pascal and volume is five temperature is equals to 100 degree Celsius so this is my first stage state one now now what I do so this is my fixed State now what I do I will start giving some heat I will start giving some heat so what will happen pressure is going to increase temperature is going to increase volume is also going to change depending upon how pressure and temperature increasing how boundary is changing so basically what I am trying to tell you these properties are going to change okay now when these properties are going to change what you can do you can mark them okay so first of all you have marked here 10 kilopascal and 5 meter cube you have marked now you are giving heat so maybe pressure is decreasing why because your boundary the Piston is expanding the cylinder you know the volume is expanding so you see your volume has increased and pressure has decreased similarly pressure has further decreased volume has further increased so you have to relate with this you are giving heat pressure is changing volume is changing and temperature is also changing and until and unless you keep giving Heat this is going to change it is going to further change so you see it is taking some intermediate pressure and temperatures to determine the path to the series or succession of state passed during a change of this is one state you see and now it is changing slowly slowly slowly so whatever series whatever points it is taking it is called as path it is called as path now eventually what will happen eventually what will happen you stop giving Heat eventually you stop giving heat so once you stop giving Heat then you will have a final pressure let us say now by volume was increasing let us say it has 15 meter cube so pressure is decreased let's say 0.5 kilo Pascal okay and temperatures Also let's say 50 degree Celsius I will tell you Abhishek don't worry about that okay now so now you now you have to stop giving heat so finally we have reached at this point so again this is my fixed State between these two states your properties are continuously changing so you cannot fix the state now this is my state 2 Okay so from coming from State 1 to state two whatever path you have taken whatever points you have taken is called as path and the complete thing from State 1 to state two is called as process is called as process okay now Abhishek is asking how many properties should require to fix the state it depends upon what kind of system you are you you are working in okay other there is a log gives phase rule that you use Gibbs phase rule p plus f is equals to C plus 2. okay so if phase is one for example only gas phase is there and component is also 1 plus 2 so f is equals to 3 minus 1 so basically if you are working in one phase you have to fix two properties so we have fixed what pressure and volume we have fixed okay but this changes this changes then you know like the phase is changing for example you are working with a mixture of uh water and air or water or steam sorry okay so it changes clear now next is reversible so processor of two type reversible and irreversible I hope all right that was not the part that I was going to take anywhere bishek okay but in detail I have told you look gives phase rule if you I'll just spend two minutes over it not much because I need to focus on some topics okay I am I really will not be able to cover everything okay so let me add some slide now Gibbs phase rule Gibbs phase rule is basically tells you that degree of freedom or the number of independent intensive properties required to fix the state of system what is the formula of gives phase rule P plus f is equals to C plus two p is what phase this is degree of Freedom or the properties components and 2 is a constant now for example you are working with water so what is water what is Phase tell me how many phases are there phase quickly tell me one phase component how many phases how many components no no no no no component is just one H2O I'm not talking about molecules here I'm not talking about elements here okay component is H2O all over you see if you have this so here is also H2O here is also H2O here and also H2O nowhere you will get o h O2 okay component is with the compound the compound is what H2 is the compound Okay so is it clear everywhere you have H2O know where you have h o two because h o two is a different compound okay now so component is also one so that is what you can say phases 1 F component 1 plus 2 f is equals to 3 minus 1 f is so for water if it is in just liquid state if it is just liquid state then you can Define by just two properties but what happens if it is water and steam then here it will be very thin you see this is then okay if you want I can do this as well I have no problem so now if water is steam then we have three then number of phases p plus f is equals to C plus 2. is it ok this thickness I think it's very thin if we have water and steam water plus steam so tell me number of phases number of phases two a number of components components component is one component is one because in water also it is H2O steam also it's H2 1 plus 2 so f is equals to 3 minus 2 f is equals to 1. so only one independent intensive property is required okay so that is how you can find out although it's not very you know like usually don't get question directly but anyway now you know let's move ahead let's move it so we were going to discuss irreversible and reversible I hope you already have heard this word so many times let me drink a sip of water and then we'll continue I think we have come what how many slides we have covered not much have you heard about reversible and irreversible processes or reversible in general and irreversible okay okay so reversible process is a process if you you see like for example you you are here you have a hill that is your Hill and you are going from here to here so of course you know like you have spent some energy some metabolic energy and some you know something is lost energy is gone but tell me one thing if you are coming back from here to here will you get this energy back no of course when you are coming down also you are going to release some more energy right so that means basically continuously when you are going up you have given some energy to the surrounding when you are coming down you are giving some energy to surrounding okay let me explain it one more time so let me increase the thickness it's not fun actually I mean it's very thin okay look this is your Hill okay you are here now when you are going up you are going up you have spent some energy now I know when you will come down you will not absorb this energy but just assume just assume that when you are coming down when you are coming down you are absorbing back this energy just assume for one second now you see you have done a process you have moved from one to two and then come back okay so basically you move from one to two then reversed and come back so in this case when once you come back whatever energy you have spent you have given to the surrounding you have absorbed back so tell me what is the net effect on surrounding in this process zero very nice because when you are going from one to two whatever energy you have spent whatever energy you have given to surrounding when you came back when you reversed back to one you have absorbed so basically you did not give anything right in this whole process from one to two then two to one net effect on surrounding is zero so if you if any process can happen in such a way it is called as reversible process okay if if any process although it is not possible it cannot happen but if it can happen it is called as a reversible process so basically if a system is called as reversible if the both the system because you see system is not net effect on system also is zero because system has spent some energy then it is absorbed back so system has not lost anything eventually okay so net effect on both the system and surrounding returns to its initial state by reversing the direction without leaving any effect on system or surrounding so if you can reverse a process in such a way that it will not affect the system and surrounding it any way then it is called as reversible process it is shown by continuous line okay it is shown by PV so I will show it okay I will show it like this one two and I will go like this I will go like the continuous line I will show okay the system as well as surrounding can be completely stored what about irreversible so the actual case you see when you are coming down you are also you know losing heat to surrounding that means net effect on system or so when you are coming back the system did not restore to its original thing okay so basically you have Disturbed the system for surrounding and when you are leaving some effect on system or surrounding it is called as irreversible process so a process is said to be irreversible if the system does not return to its initial State due to impact left on the surrounding and the system and surrounding cannot be nor surrounding a system nor surrounding can be completely restored to its initial condition okay it happens and that is the reason it can only happen in One Direction okay it is represented by dotted line you can only show it by dotted line yes someone has raised hand or something I think who is this which is shown by this in reversible we can say that there is no loss of energy of system and surrounding as well that is the reason no like both both the system is surroundingly restored whatever surrounding absorbed it gave back whatever system has absorbed it gave back okay who raised the who raised some hand someone was who knows that okay any question anyone else okay I don't want to raise hand why I raised hand okay what are the forms in which system can lose the energy [Music] system can lose energy in any form it can lose basically look there is one with some loose energy and that is heat that is the most common way of you know losing energy in fact most of the systems in fact heat is the byproduct of anything okay so most of the energy is always lost in terms of heat and if you are not low if you are not using any energy but you see look pressure look you have to understand one thing Ravi Teja what is pressure pressure is basically the average momentum of atoms or molecules okay so if I'm if I am you know like system is at high temperature high pressure that means reversible system is possible in no it's not possible no it's not possible there is no reversible system you cannot lose pressure basically like you know pressure will be lost in other terms for example energy will be going out so if energy is going out the temperature of the system will reduce or and in you see its density may change and then pressure loss will happen okay pressure is not crossing the boundary okay what is crossing the boundary energy is crossing the boundary okay so if energy is crossing the boundary it is the after effect that the pressure is decreasing or increasing okay so pressure loss we in general times we say pressure loss but it is not the pressure that is losing yagna no there are no uh real reversible systems uh reversible process or reversible systems okay so let's move ahead now thermodynamic cycle thermodynamics what is the cycle you tell me what is cycle cycle is basically you start from somewhere you're asking for reversible and irreversible processes look they are reversible process example there are no reversible processes irreversible process example all the processes around you are irreversible for example you have moved your hand it is a irreversible process you have walked from your room to your kitchen it is irreversible process okay all the processes are irreversible whatever you do whatever happens around you is an irreversible process okay yes yes I'm saying that is correct we are losing energy only okay but pressure is basically it is happening in terms of pressure pressure is the after effect is happening inside the system okay now foreign cycle is what it basically repeats its state it basically comes to its original state okay you start from here you go here you go you go here then you go here then you go here then you go here then you go here but as soon as you reach back you have completed the cycle so for a cycle pressure is not work energy work you can utilize you can do work using pressure okay look don't don't do please do not you know mix the words you have to understand that if the pressure is high you can utilize more work out of it okay so pressure is not an energy you first of all you have to understand pressure is not an energy okay pressure is a property work is energy okay so you know I'll tell you one thing and it's a very funny thing teaching you know like teaching if you when you teach you know students you have to be very cautious because if you tell them so many things things then they will get confused you see if if I if I'll just tell you very few things then you will be very happy okay I understand everything but when you explain so many things no so because you have a very raw mind so you cannot differentiate between pressure and energy you are confu you are you know mixing pressure energy I told you pressure is a property work is the energy okay they are completely I mean they are different they are not same so you cannot say pressure is like a work energy so what I'm trying to tell you is do not try to you know like uh mix everything up just you know chill study and then try to revise things and thermodynamics is a subject that you will never understand the very first time whoever is studying the very first time you will be very confused after read after you know learning it it's a minimum three revisions are required to understand thermodynamics minimum okay you will slowly start getting things do not worry about it okay hello let's move ahead let's move ahead so basically if you are coming back to the original state so cycle means cycle means initial state is equals to final state okay so minimum number of processes are minimum two required okay one you will go and then come back to minimum to do then it can be three it can be four four how how 4 will look like we will start from here you will go like this you will go like this you will go like this and then four five it can be anything it can be any number of processes so but the minimum is 2 but the minimum is true and for the cycle difference of all the properties is zero we will understand this in some time but just note it down for I mean just understand this for a cycle change for a cycle change in property will be equal to zero just uh no I'm not explaining this I will explain this in some time okay not now but just you know keep this in your mind that what I am saying okay let's move it now point and path function point and path function so what is point and path function so as the name is suggesting first of all let's understand path function okay my cursor is creating some disturbance what type of disturbance okay yeah yeah that that is my pen that is doing some disturbance okay I I mean there's a button here if I click it just you know does something so listen let's understand path so what the path function means path basically a function that depends on path simple words okay if we have a function that depends on path is called as path function what does this mean it actually means for example you see Loop I have a PV diagram I am going from 1 to 2 by using a path a okay now I am going with this path path P or I am going with this path see so tell me if I have a property that is a path function okay if I have a property that is a path function so will it be same let me let let's take a property X so will this property or change in this property for path a will it be same for path p ath C is it correct or not you tell me this do you think no of course not because you see this is let us say this is X1 and this is X2 okay so if I am going from path if I am going from path a then my change and it is going to depend on path so my okay yeah sorry so my change in x from path a will be will not be equal to X2 minus X1 simply okay okay so basically you see I or I can tell you in this way you see when I am taking this path a path so this area it is covered is this right when I am taking B path the area that is covered by this path is the red one when I am taking this C path so area covered is this one okay so the area covered with each path is different okay and if a property is going to be a path function then if you change the path that property will change you cannot simply just write x 2 minus X1 okay so basically a path function depends on the path followed by the process its value dependent on the path followed so its value is going to depend by what is my X2 what is my X1 what is the final change it is going to be dependent so it is they are not equal they depends on the path so Delta x a will not be equal to Delta X we will not be equal to Delta x c okay for example heat and work are path function again we will discuss this but don't worry about it now okay just know that heat and work our path from path okay now I would say a point function now Point function what is the point function it is independent of path so it does not depend on path now whatever path I am taking as long as my first state and second state is fixed so whatever path I am doing a b c or any path but I am starting from here I am reaching here as long as my initial and final state is same the value of let me say Point function as y okay so Y is a point function so change in y for path a will be equal to change in path uh Y in path B It Whatever path you are taking you attain C path you are taking D path you are taking e path whatever path you are taking as long as my 1 and 2 is same change in the point function will remain same it does not matter and a point function is called a property of a system a point function is a property a path function it is not a property you have to understand this vertical and it is not a property so heat and work they are not a property of the system okay heat and work pressure temperature volume enthalpy internal energy entropy they are all properties of a system okay so now I can tell you this thing now I can tell you this statement that change in property so again look I started from here so my property let us say was P2 okay then my fi for a cycle change in property for a cycle to change in property for a cycle is equals to whatever so what is genuine Property final position minus initial position now my final position is what P2 for at this point and initial position is what also two so also it is 2 for a cycle I am saying because cycle I started from here and I reached back okay so it will be equal to zero it does not matter I go I take this part I take this part as long as I am coming back here change in property will remain zero because it is the properties for property depends on only the state only the point where you started or where you ended okay so whatever path you are taking does not matter okay so that is your point and path function now these things is very important work and heat transfer are path function they are not properties basically path function they are not properties just simply know this okay now exact and in exact differential exact and so it is also similar to path and point function you see Point functions are exactly differential what do you mean by Point functions are exact differential so exact differential means cyclic integral of the point function will be equal to zero cyclic integral okay so you see I started from 1 to 2 and then came back at one okay so change of property at now what is cyclic let me write it here so the cyclic integral of a variable is equal to zero exactly differential that means cyclic integral of a property will be equal to zero of a change in property okay so what is cyclic the cycle it is starting from you know so when I say this so I can I write Delta P A Plus Delta p b is equals to zero cycle means what this plus this oh sorry this plus this yes now it is equals to 0 for exact differential so I can write Delta p a is equals to minus Delta p B okay now what is this change in property by a path so I can write P2 minus P1 what is this B so B is final minus initial so it will be minus P1 minus P2 so if you reciprocate this it is P2 and P2 minus T1 it's simply telling you that does not matter if you are taking PATH a or path B you can simply write P2 minus P1 simply you can write the same okay that's why you see look that's that's how you do like for example if you want to calculate change in enthalpy for path a so what do you do H2 minus H1 you have to calculate change in pressure for path a what will you do P2 minus P1 simply okay so you can write it in this way but but in exact differential the cyclic integral is not equal to zero any key this Delta P it is not equal to 0 that means these things they are not equal to they are not equal okay they are not equal that is the reason that you can never calculate change in work for path a have you seen this equation anywhere tell me work two minus work one or change in heat a is equals to Q2 minus q1 have you seen this equation anywhere yes or no [Music] yes you cannot see this because these are path function you cannot calculate simply by this you have to integrate for example you are taking this path you will take little area and then you integrate it for the whole area and you will get this then you can calculate so it will be basically equal to area okay we will see this when we come to work and this is also area okay but what I want to what I want to tell you is path function cannot be calculated like this it is not correct it is not correct but Point function you can directly calculate like this Delta volume change in volume in the process a V 2 minus V1 change in entropy is equals to S2 minus S1 for all the properties you can do this this but for work or heat you cannot do this because they are path function okay is it clear yes or no okay so let's move ahead then thermodynamic equilibrium thermodynamic equilibrium okay now anyone any idea about what is thermodynamic equilibrium a lot of people confuse thermodynamic equilibrium with thermal equilibrium in the interview they will ask you what is thermodynamic equilibrium you will start telling thermal equilibrium they are not equal they are not equal pranjul look it will be really a tough you know like I have to explain so many things what you can do is this recording you please just check it once you just try to understand grasp you know absorb it slowly if you have any doubt we will have next class you can ask that out because if I again please it's a humble request if I start explaining everything again no then it will be little difficult to cover everything okay please so you see the recordings it will be available tomorrow I think maybe tonight just see it absorb it if you don't understand ask in the next class okay but come up with a specific doubt if you just say sir please explain again then it will be really difficult okay so just ask some specific doubt he said okay how are you doing this how are you doing that I will be more than happy to answer okay so so thermodynamic equilibrium basically a system is said to be in thermodynamic equilibrium when it satisfy three conditions whether three conditions mechanical equilibrium thermal chemical equilibrium and thermal equilibrium okay these three conditions must be satisfied now what do you mean by mechanical equilibrium mechanical equilibrium simply means that there should be no imbalance Force Within within the system and between the system and surrounding there should not be so basically if this is your system here pressure is equals to what is the pressure outside surrounding one atmosphere so this should also be at one atmosphere because for example if it is a two atmosphere so there is an imbalance Force between system and surrounding you see inside pressure is higher outside is one second let me complete this then I'll read what you have written something long okay so what I'm trying to tell you is that if this pressure is not same between system and surrounding then there will be some imbalance at the boundary so you cannot say that it is in mechanical equilibrium so basically you can say mechanical equilibrium is equality of pressure equality of pressure okay what is chemical equilibrium chemical equilibrium is basically no chemical sorry no chemical [Music] reaction inside the system okay so if there is no chemical reaction so there will be no change in chemical composition chemical composition of the system okay so that we were in in that Gibbs phase rule if you take H2O so yeah composition means it has hydrogen oxygen but component is one only okay so you have to yes rate of back for basically there is no reaction that is happening okay so you you cannot say that rate of forward reaction or rate of backward reaction it can actually you know like uh still if you say rate of forward and backward means component is changing okay but there is no chemical reaction in simple words there is no in thermodynamics we basically neglect any chemical reaction in our system okay so basically here the criteria is equality of chemical potential chemical potential now thermal equilibrium is same it is basically equality of temperature so between system and surrounding there will be no inequality of temperature so if these three conditions are satisfied so you see thermodynamic equilibrium is not equal to thermal equilibrium it is a part of thermal thermal equilibrium is a part of thermodynamic okay so if all three conditions are satisfied then only you can say that thermodynamic equilibrium your system is in thermodynamic equilibrium okay now serum was saying something if thermodynamic process returns to its original position then we can say that the cyclic integration of work done is zero no you cannot say that how can you say that you see let me go back let me add a page so you see this TV once you go from here to here okay one two two you have you have done some work okay you go so that it will be work in the process a so basically while going from one to two now when you go from two to one of course you will not go back because if you are going back in the same process it is a reversible process reversible process is not possible okay so you cannot take this process you will have to take some other process so you will take what you will take this process okay now it will be the now w b it will take so cycle is completed yes it is returned to its original state but w a is not equal to WBY what is w a w a is this the area under the curve what is WB WB is this area under the whole curve this one and they are not equal so if they are not equal you cannot say cyclic integral of work is equal to zero it is not how it is zero if it is equals to 0 that means uh then I have to write w a plus W B is equals to 0 and W A is equals to minus WB but this condition is not satisfied no I am saying it is not same okay yes following same path means reversal process Shivam is saying uh force of one zero we need to follow same path yes same path you have to follow done by system is equal to heat absorbed that is for a cycle yes but again heat transfer we are not accumulating for heat trans rate transfer will be something else okay so heat transfer here work transfer is happening W A plus W B is equals to q a plus q b neither this is same nor this is same okay so cyclic integral of Z of work is 0 is a completely different story and this is completely different story okay foreign that is completely different okay so TK let's move at thermodynamic equilibrium is done ideal gas equation quickly let us what is the time okay not much time left we still have to cover a few things let's quickly let me move ahead okay so ideal gas law there is nothing much to I think you are or you have already learned this in 11th and 12th okay so basically ideal gas law is defined by using Three Laws Boyle's Law Charles law avocado law okay boys loss says that at constant temperature and number of moles okay number of moles if we have constant temperature and number of moles volume is inversely proportional to pressure volume is in it is experimentally defined okay it is experimentally defined they kept temperature constant and number of moles constant and what they saw that when volume is decreasing your pressure is increasing and when volume is increasing your pressure is decreasing that means they are inversely proportional okay then again experimentally Charles defined that if you take pressure and number of moles as constant then volume and temperature are directly proportional so if volume is increasing temperature increases if pressure is constant again mark my words if pressure is constant then this will happen okay and if volume is decreasing temperature is decreasing law was experimentally again defined at constant pressure and temperature volume is directly proportional to number of moles so we have just combined volume volume we have combined this and we have got PV is equals to nrt P is our pressure absolute pressure okay V is the volume n is number of moles T is absolute temperature and R is universal gas constant and its values it is it always remains same 8.314 Joule per mole Kelvin now this is the equation that mostly chemical Engineers use chemical Engineers why because it has number of moles n is number of moles so they mostly use this equation we do not use this okay as a mechanical and Aerospace I mean we use this but not very frequently what do we use we use in terms of mass so what is happen by n is number of moles number of moles is what Mass upon molecular weight okay so let me substitute n here and I will get this okay now let me take n as outside and capital r plus molecular weight and this is called as R which is characteristic gas constant characteristic gas constant so again remember these words number of moles is equals to mass upon molecular weight and specific gas constant is equals to universal gas constant upon molecular weight now this is characteristic gas constant it will be different for each gas for air it will be different for you know carbon dioxide it will be different for each gas it will be different so for water you can write it like this r is equals to because what is the molecular weight for water 18 H2O okay molecular weight is what 16 plus 218 and for air actually it is water vapor okay it is Steam we are only talking about gas for air it is molecular weight is continuous so you can these are very common otherwise they will be given to you you can calculate for nitrogen as well okay so if you know the molecular weight you can calculate characteristic gas constant so I we use basically this equation mechanical engineers and aerospace engineers mostly use this equation although we use that as well but most frequently use this okay so this is your ideal gas equation now it is basically equation of state of a hypothetical ideal gas it gives you good approximation of real gas basically we all know that there is no ideal gas but when real gas is at low pressure and high temperature mark it is objective question when real gas is at low pressure and high temperature then it approximates as ideal gas real gases low pressure and high temperature behaves as ideal gas and you can apply PV is equals to MRT at this condition now what happens if it is not showing if it is at high pressure for example and low temperature that means you cannot apply ideal gas equation you cannot apply it then what will you do there is a variable actually there are different equation equations of State like wonderful equations and all but a simple version is you account for a compressibility Factor it accounts for a compressibility factor so for you see PV is equals to MRT now P mass per unit volume into RT p is equals to specific volume upon RT it will be volume upon one second sorry it is density this is density let me not write it like this let me write volume per unit mass is equals to RT specific volume upon RT so specific volume upon RT is constant okay now in order to ideal gas to satisfy this constant must be 0 but for real gases it is not equal to zero this constant is called as compressibility Factor Z okay it is called as Z so Z is ideal gas for idle at equals to 1 for real gas it is not equals to 1 it deviates from 1. what is 0 y 0 did I say 0 somewhere Z is equals to 1 I set I don't know what 0 you are saying is it clear this much is clear tell me yes or no quickly okay so let us come to the last topic of today which is zeroth law okay simple law it basically tells you it states that Eva body a is in thermal liquid with body b m body B is in thermal equivalent with body C separately so let us take a body let me call it as B okay now let me take a body a now what I am saying is if this body a is in thermal equivalent with body B simple when will be in thermal equilibrium with B when its temperature and its temperature will remain same okay okay I don't know this temperature I don't know this temperature let me say t but um these A and B will be in thermal equivalent when their temperature will be same that means if T is equals to TB now let me take one other body see and I am saying DC this is t a let us say okay and I am saying this C is also in thermal equivalent with body B okay when will this happen when this both it will happen or look again let me rephrase this again I have a body B and I let me bring in contact with this body p and its temperature is not going to change so what does it indicates okay if you are bringing two bodies together and their temperature is not changing what it simply means that their temperature is same okay so that means T A is equals to T B now I am taking that body B somewhere else and I am joining it with body C and still their temperature is not changing that means T C is equals to T B okay and if this kind of scenario is there that means A and C are also in thermal equilibrium A and C are also in thermal equilibrium okay you do understand this but I have a body I have I have one body and now I am bringing a body in contact with this and their temperature is not changing that means that temperature is same okay now I keep my what first body as it is now I bring a third body and bringing back to the first body they are in contact and their template is also not changing that means they are also in thermal contact that means both body A and C are in thermal contact thermal equilibrium okay so it states that if body is in thermal equivalent with body B and body B is in thermal equilibrium with body C separately then body a and c will be in thermal equivalent with each other okay so this is the conclusion so basically here we take a reference body so this is a reference body which is used to determine the temperature and this reference body is called as thermometer okay and there will be one property that will be changing when I bring these two bodies in contact if the temperature is changing if the temperature is changing that means it is it will be indicated through a certain property and that property on which the property of these bodies on which temperature is dependent is called as thermometric property okay so again I could you know like I could spend a lot of time in this explaining but I am intensely not I usually you know like spend a lot of time I actually take a two hour lecture on zeroth law of thermodynamics but I am not because I think it is not very important for you but I I mean I know it could it could be there so I am covering all the basics that is required okay so so basically you have a thermometer and you have a thermometric property to measure the temperature these are two main things okay so there are various types of thermometers first is I am not covering the working of these just you know the important points so we have resistance type thermometer it works on wheat stone bridge and the thermometric property is resistance so basically if the resistance is changing its temperature is going to change you see if the temperature is changing if the resistance is changing you see uh that is called as weak Stone Bridge right this is something like this galvanometer and all and we connected with the supply and we Supply Power we take resistance is constant in all of them only one resistance I'll let change so based upon the current that it is showing the resistance is going to change and this resistance a change in resistance will tell you the change in temperature so basically resistance is dependent on temperature both temperature is dependent on resistance that's why resistance is called as thermometric property okay now the next one is thermocouple thermocouple also you may have heard okay and the principle is C back effect see back effect okay and it's thermometric property is potential difference or voltage difference mercury thermometer to you all have seen right and the normal thermometer that we use you put it in your mouth or somewhere and the Mercury expands Mercury expense so its volume changes yes or no or or you see the length the length scale on the if this is your mercury thermometer then the volume of Mercury Rises up so basically there are scales here right so based upon scale you can read the temperature okay so based upon the change in volume or change in length you can read the temperature okay now there is constant volume thermometer here thermometric property is pressure and constant special thermometer here the properties volume okay very quickly let us see uh you know a little bit of will wrap up it at 11 okay now you know like there was no method of measuring the temperature when the Roth low came and there was no method of measuring the temperature like we had no thermometer Okay so we basically defined some methods to measure the temperature so thermometer came much after that okay so we defined separate methods of uh you know to measure the temperature and the measurement process is quite random like there is no basis for it okay you say 0 degree celsius but how do you measure zero degree celsius okay there is no point in saying that okay ice is you know like uh you say ice melts are zero degree uh Celsius or it freezes at zero degree celsius but what is 0 degree celsius it has no physical significance of it you can say it is 100 degree celsius as well nobody is going or Ike you are saying it is 0 degree celsius I can say it is 50 degree uh X whatever it is it's up to me how I want to Define this it's very arbitrary you want Celsius is a person who has said that when the ice freezes I will say zero when the ice boy when the water boils I will say 100 boiling point it is my choice I can I can say 250 as well here it's I can just convert it in some way okay so temperature scales are arbitrary as you show as you wanted as the you know as these people who were working on these experiments as they wanted they defined it there was no you know uh quick or say stick this section on that okay so in order to be able to assign a number to the temperature of a body it is necessary to agree upon a method for setting up the temperature scales so we need to choose the thermometric property so we can choose any property we can choose a length or the right stance or the pressure and we will call this property as X we will call this property as X during the calculation of the temperature okay so the first method that we used was before 1954 and it was based on two reference points ice point and steam Point okay linear temperature we look what is X thermometric property and I have just told you that temperature depends on this property now how does it depend we took a linear relationship okay now I have fixed two points I have I have you know I have I had water and I fixed ice Point as 0 degree celsius and steam point at 100 degrees it was my choice if I was someone else I can take it as anything but Celsius to 0 degree celsius and 100 degree celsius and at this point the property is x i i means eyes and here property is x s which is Steam okay so x what is this this is thermometric property at ice point whatever the value is it does not matter but at that point thermomatic property at steam point okay now what do we have we have a linear relationship so what will you do by we have T is equals to a x plus b so let us take ice Point let us take ice point so temperature is what 0 a x i plus b so we can calculate B from here B is equals to minus a x i okay now let me take a steam Point hundred is equals to a x i plus b okay so from here I can say 100 100 is equals to a x h sorry a x s minus I can put the value of B here minus a x i so it is a x s minus x i so what is a is equals 200 upon property at Steam and Ice point so now I have gotten a and b i can substitute in my main equation so T is equals to 100 upon x x minus x i x Plus minus actually minus a x I okay and what is a a is again same what is a is 100 x s minus x i into x i okay so I can take 100 x x minus x i x minus x i so I can eventually write this as T upon 100 is equals to x minus x i upon x x minus x i okay so this is my general equation this is my general equation or what can I do you see these values are known already it will be given to you now they will say calculate temperature when X is equals to 5. so you know this you know this you know this you put five here and we will calculate temperature in degree Celsius in degrees celsius this is degree Celsius scale okay so here temperature is basically what is this temperature is a function of the thermometric property okay so that is how we have defined this you see now Fahrenheit basically we can convert this we can convert this into several forms for example what do we have T minus t i upon t s you see this is what what is this form can I say it is T minus t i upon 100 100 is what t s minus t i is equals to x minus x i upon x x minus X I can I say this because you see if I put 0 and TS is what hundred minus 0 so I will get the same result yes or no can you tell me yes or no same result we are getting no okay so we can use this so we have t s minus t i is equals to x minus x i e upon x x minus x i okay so in degree celsius I have T minus 0 upon 100 minus 0 is equals to x minus x i upon x x minus x i what about in degree fair in degree Kelvin let us say Fahrenheit so I have written it here what is in kelvin what is ice point in Kelvin ice point in Kelvin yes 273 and what is steam Point 373 minus 273 is equals to x minus x i upon x x minus X Y similarly you can calculate for fahrenheit as well okay so this is the conversion of one scale to another scale so for example you want to convert U Fahrenheit uh degree celsius to fahrenheit you can use this relation M convert it okay so this is how you can use this last is after so this was before 1954 after 1954 basically we have several problems with the you know the previous method because you have to first of all calculate two ah temperatures ice point and steam point now anyway it was very difficult to calculate you know to measure the temperature it was very very difficult at that point of time and now you are measuring two temperatures so basically the margin of error was higher so what did they do they bring it back to one single point and that point is called as triple point triple point okay so here we use ideal gas equation now this is based on a single point based on single temperature reference okay so we took ideal gas equation and P is equals to m r by T temperature is directly proportional to pressure and we have taken a proportionality constant k okay now we have defined temperature triple point temperature is of water is 273 and pressure is 0.611 okay now what will I do I have this relationship T is equals to k p now I can do I can put TTP is equals to K pressure at triple point so K is equals to TTP upon p t p now I can substitute the value of K here and temperature is equals to TTP upon PTP into p and what is this 273.16 pressure upon you can put the value of this as well but usually it is written like written like this okay so temperature is equals to 273.16 P upon PTP so if you at a given pressure if they say calculate pressure a calculator temperature at the pressure of 100 kilo Pascal so you put this here calculate temperature so this is how they started measuring this okay so there were you know like ah can have a different all the resistance thermometer and all that you can Define based upon this equation as well okay so I hope this is it for today I know that we have covered a lot but because it is a two hour class so we will be covering a lot anyway each and every class how you can benefit with this is you have to revise because uh okay today's session was completely isolated uh most of the things we are not going to use later on but there are so many Concepts that we covered but from next sessions we will be covering so many Concept like work transfer first law a heat transfer processes different processes uh constant volume concentration all that and we will be using them each and every day so revision is very important if you are not revising you are not utilizing the what I am trying to give you okay so please revise I have tried to cover most of the important things that is required from example interview for any competition point of view I would say okay so please revise and we will meet in the next class I don't know when we will meet but it will I think it will be communicated to you okay so let's stop here already uh it's been it's 11 yes foreign