[مجموعه ویدیویی آموزشی] - ترمودینامیک Thermodynamics - به زبان انگلیسی

[P O U R I A]

سلام
در این تاپیک یک دوره کامل اموزش درس ترمودینامیک رو میخوام برای دوستان قرار بدم.
این دوره انگلیسی هست. ولی برای اینترنشنال هاست و کاملا قابل فهم و ساده صحبت میکنن. برای برای یادگیری لغات مرتبط هم بسیار کاربردی ست.
متن صحبت ها هم در هر پست گذاشته میشود.

 

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Lecture 1: Introductory Topics > Introduction Previous

Lecture 1: Introductory Topics > Introduction Previous

Greetings from Mumbai and greetings from IIT Bombay.
Welcome to the edX and IITBombayX course, ME209x.
The title of this course is Thermodynamics.
I am Uday Gaitonde. I am one of the teachers for this course.
I will be helped in teaching of this course by two of my colleagues Milind Atrey and Upendra Bhandarkar.
All three of us are on the faculty of Mechanical Engineering at the Indian Institute of Technology Bombay at Powai, Mumbai.
To begin with let us briefly look at the prerequisites for this course.
These are the topics and subjects which you are expected to be familiar with,
so that you can appreciate and go through this course without any significant difficulty.
It is expected that in high school, you would have studied physics and chemistry.
In chemistry, we are mainly interested in physical chemistry.
The mathematics requirement is slightly at a higher level.
So, let's say at the junior college level, you should have studied mathematics,
particularly the calculus part of mathematics, and in calculus we will be essentially looking at,
differentiation and integration as the two main requirements,
but we will also be using, partial differentiation and will make use of some properties of exact differentials.
Apart from this background in physics, chemistry and mathematics it is expected that you should have the ability to work with numbers.
You should not hesitate to use a calculator and do some amount of number crunching for this course.
What about textbooks?
It turns out that although a large number of textbooks are available for the circulate on thermodynamics at various levels,
it turns out that there is no perfect textbook of thermodynamics.
It is also not possible to have one single textbook which aligns itself perfectly with this particular course ME209x.
However, since a reasonable number of good textbooks are available, I will be listing a few of them.
They will be available in a separate document just after this video.
So, the recommendation is go through the list of books, look them up, in the local library and may be select, a few for reference.
The books listed include engineering-oriented books. The books listed include some classical physics books.
So the choice is yours.
I recommend that you browse through these books whenever time permits and then decide which one or which ones you will follow.
Thank You!​

 

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Lecture 1: Introductory Topics > Engineering and Thermodynamics

Lecture 1: Introductory Topics > Engineering and Thermodynamics

Engineering and Thermodynamics

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We will now look at the place of thermodynamics in mechanical engineering and in engineering.[/FONT]
[FONT=comic sans ms]First let us consider what is engineering all about?[/FONT]
[FONT=comic sans ms]It is a bit difficult to provide a simple definition of engineering,[/FONT]
[FONT=comic sans ms]but let me make an attempt.[/FONT]
[FONT=comic sans ms]Let us say that on one side we have nature, on the other side we have us, humans.[/FONT]
[FONT=comic sans ms]Nature provides us resources.[/FONT]
[FONT=comic sans ms]Water, air, solar energy, stored energy in the form of fuels of various kinds, many minerals.[/FONT]
[FONT=comic sans ms]What we want is a good life.[/FONT]
[FONT=comic sans ms]So what we do is to use the resources of nature to provide us a good life.[/FONT]
[FONT=comic sans ms]This can generally be called engineering, and the people who do this are engineers.[/FONT]
[FONT=comic sans ms]This turns out to be a rather wide definition of engineering,[/FONT]
[FONT=comic sans ms]but I think most of us will agree that it is a reasonably nice way to define engineering.[/FONT]
[FONT=comic sans ms]It is a wide thing - mechanical engineers, in fact many people like tailors, cooks, cobblers,[/FONT]
[FONT=comic sans ms]which we generally don't consider as engineers, can also be considered engineers from this definition of engineering,[/FONT]
[FONT=comic sans ms]and I don't think there's anything wrong with this definition.[/FONT]
[FONT=comic sans ms]Now, this course although it is of thermodynamics will have a mechanical engineering flavour.[/FONT]
[FONT=comic sans ms]In fact, a significant flavour of mechanical engineering, because the background of all the three teachers who are involved in this, is that of mechanical engineering.[/FONT]
[FONT=comic sans ms]So let us see what mechanical engineering is all about.[/FONT]
[FONT=comic sans ms]The scheme is similar, we are now trying to define what mechanical engineering is all about.[/FONT]
[FONT=comic sans ms]Again we begin on one side with nature and here the resources that we are going to look at is energy resources quite often known as fuels plus materials,[/FONT]
[FONT=comic sans ms]which are available in nature.[/FONT]
[FONT=comic sans ms]On the other side is ofcourse the good and comfortable life for us.[/FONT]
[FONT=comic sans ms]Now, mechanical engineering essentially does use the resources of nature to provide us good life but it does it through what we generally call machines.[/FONT]
[FONT=comic sans ms]The machines we look at are of various kinds.[/FONT]
[FONT=comic sans ms]One set of machines will use the natural resources energy and materials to provide energy, at a certain rate we call it power.[/FONT]
[FONT=comic sans ms]And ofcourse we will use energy for good life for say transportation and to drive machines.[/FONT]
[FONT=comic sans ms]We will also have machines that produce machines and we have machines that produce gadgets, and machines of all kinds that directly or indirectly provide us with good life.[/FONT]
[FONT=comic sans ms]So this, I suppose, is a general scheme of mechanical engineering.[/FONT]
[FONT=comic sans ms]Now, where does thermodynamics come in?[/FONT]
[FONT=comic sans ms]We will notice that one of the schemes in mechanical engineering was machines that use natural resources and produce energy,[/FONT]
[FONT=comic sans ms]which we can use for driving our cars, running our refrigerators, washing machines and anything that we see.[/FONT]
[FONT=comic sans ms]The natural resources are usually in the form of fuel.[/FONT]
[FONT=comic sans ms]I put fuel in quotes because, even solar energy may be considered as a fuel of some sort.[/FONT]
[FONT=comic sans ms]This provides energy in the form of heat.[/FONT]
[FONT=comic sans ms]You stand in the Sun, you feel warm[/FONT]
[FONT=comic sans ms]We burn some fuel, it is liberated.[/FONT]
[FONT=comic sans ms]Whereas, this energy which machines produce is in the form of work.[/FONT]
[FONT=comic sans ms]The science which looks at such machines which convert heat to work and may be even vice versa wherever it is needed is known as thermodynamics.[/FONT]
[FONT=comic sans ms]So thermodynamics is essentially going to look at stuff which interacts doing or absorbing work and which interacts doing and absorbing heat.[/FONT]
[FONT=comic sans ms]And these could be machines, these could be gadgets, this could be anything.[/FONT]
[FONT=comic sans ms]In thermodynamics, we just call these thermodynamics systems, this word we will define again later.[/FONT]
[FONT=comic sans ms]Although, thermodynamics was initially developed by engineers looking at engines, pumps, compressors, fans,[/FONT]
[FONT=comic sans ms]as the science developed it turns out that thermodynamics is a proper branch of physics.[/FONT]
[FONT=comic sans ms]If you take up any good book on higher level of physics we will find a chapter at least a chapter on thermodynamics along with mechanics,[/FONT]
[FONT=comic sans ms]fluid mechanics, electricity, magnetism and others.[/FONT]
[FONT=comic sans ms]The contributors to thermodynamics come from all fields.[/FONT]
[FONT=comic sans ms]Engineers have contributed to it, physicists have contributed to it, chemists have contributed to it,[/FONT]
[FONT=comic sans ms]even mathematicians have helped in formalising the science of physics.[/FONT]
[FONT=comic sans ms]And ofcourse this list is not complete.[/FONT]
[FONT=comic sans ms]And the users of thermodynamics are all types of scientists and all kinds of engineers.[/FONT]
[FONT=comic sans ms]Among engineers perhaps mechanical engineers use it the most followed by chemical and metallurgical engineers.[/FONT]
[FONT=comic sans ms]Even aerospace engineers, electrical engineers, you name it, they will be using thermodynamics.[/FONT]
[FONT=comic sans ms]Thank You.

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Lecture 1: Introductory Topics > Primitives

Lecture 1: Introductory Topics > Primitives

Since, thermodynamics is a part of physics, thermodynamics has to live peacefully with other branches of physics.
It turns out that, many quantities defined in other branches of physics - many concepts, laws,
which are available in other branches of physics are used by thermodynamics without questioning them.
For example, the laws of mechanics, the laws of fluid mechanics, the laws of electricity and magnetism
laws of gravitation - these are all accepted by thermodynamics as true because,
they have been developed by other associated branches of physics.
Such things which are defined in other branches of physics, and used by thermodynamics are known as primitives in thermodynamics.
There are many sciences from which thermodynamics derives its primitives.
For example, geometry. From geometry we will be using the concepts of length, area, volume.
And all the properties of length, areas, volumes and other geometric identities which we have derived - they are accepted
in thermodynamics as true - they are primitives in thermodynamics. We will not be defining them again.
From mechanics, we will be using ideas of velocity, kinetic energy, potential energy and any other thing which is needed.
From electricity, we will be using charge, current, voltage, electric power, etc.
There are two ideas which lie on the borderlines of primitives and concepts of thermodynamics - these two ideas are work and energy.
Both are defined in other branches of physics, work is defined in mechanics, fluid mechanics, electricity and magnetism.
Energy is defined in almost all branches of physics - there are various components of energy.
So, these two will form the links, between other branches of physics and thermodynamics and we will be redefining them in thermodynamics.
While doing this, we will see to it that we are not disturbing their characteristics as discussed in other branches of physics.
Thank You!​

 

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Lecture 2: Basic Ideas and Definitions > Thermodynamic Systems

Lecture 2: Basic Ideas and Definitions > Thermodynamic Systems

Basic Ideas and Definitions 1

[FONT=comic sans ms]Now, we are going to look at some basic concepts in thermodynamics.[/FONT]
[FONT=comic sans ms]This is necessary so that we know what we mean.[/FONT]
[FONT=comic sans ms]There are a number of terms which are used in thermodynamics, which we also use in other parts of our life.[/FONT]
[FONT=comic sans ms]One such very common word is a system.[/FONT]
[FONT=comic sans ms]We are going to define now what we mean by a thermodynamic system.[/FONT]
[FONT=comic sans ms]The word system is such a common word in english that it is used under various conditions.[/FONT]
[FONT=comic sans ms]For example, we have a system of equations.[/FONT]
[FONT=comic sans ms]We have solved a linear algebraic system of equations in high school.[/FONT]
[FONT=comic sans ms]We have political systems, we have economic systems, we have social systems, we have a family systems and what you have.[/FONT]
[FONT=comic sans ms]In computer science we have operating systems.[/FONT]
[FONT=comic sans ms]But now we are going to look at thermodynamic system and in this course the word thermodynamic system will turn up so often that the initial part 'thermodynamics' may often be neglected and we may just say 'system'.[/FONT]
[FONT=comic sans ms]So in this course whenever we say system remember that what we mean is a thermodynamic system.[/FONT]
[FONT=comic sans ms]In fact this is going to happen quite often, when we talk about 'thermodynamic system', we will shorten it to 'system'.[/FONT]
[FONT=comic sans ms]When will about thermodynamic interactions, we will simply say interactions;[/FONT]
[FONT=comic sans ms]because otherwise every time we will be using the word thermodynamic - perhaps too often.[/FONT]
[FONT=comic sans ms]Its just not worth doing that.[/FONT]
[FONT=comic sans ms]Now what is a system or what is a thermodynamic system?[/FONT]
[FONT=comic sans ms]For us, a thermodynamic system is essentially a region of space bounded by or with well defined boundaries.[/FONT]
[FONT=comic sans ms]Boundary or boundaries - singular or plural - is left to us.[/FONT]
[FONT=comic sans ms]This boundary is important because a system in general representation would be a region of space[/FONT]
[FONT=comic sans ms]and the boundary may be defined as this boundary or sometimes to emphasise that this is the boundary we align it or overlay it with dashed lines.[/FONT]
[FONT=comic sans ms]We will see illustrations of real life thermodynamics systems later.[/FONT]
[FONT=comic sans ms]But in general we would say that some region of space with well defined boundaries.[/FONT]
[FONT=comic sans ms]Now, when we say well defined boundaries remember that these boundaries may be real as in case of a surface or they could be defined geometrically.[/FONT]
[FONT=comic sans ms]They could be rigid, they could be flexible.[/FONT]
[FONT=comic sans ms]Take for example this bottle, it contains water - of course some water and air.[/FONT]
[FONT=comic sans ms]So I could say that look whatever is inside this bottle is my thermodynamics system.[/FONT]
[FONT=comic sans ms]So the contents of the bottle - water and air - are part of my system.[/FONT]
[FONT=comic sans ms]And what are the boundaries?[/FONT]
[FONT=comic sans ms]The inner surface of the bottle - it's geometrically defined - some crooked thing but we would say that in spite of the complexities of the surfaces at the bottom,[/FONT]
[FONT=comic sans ms]sides and near the top we will say it's roughly a cylinder - may be a narrowing portion on the top and with a cap closing it.[/FONT]
[FONT=comic sans ms]So whatever is the inner surface of this bottle are the boundaries of my system.[/FONT]
[FONT=comic sans ms]Whatever is inside are the contents of my system.[/FONT]
[FONT=comic sans ms]In this particular case the boundaries are physically defined.[/FONT]
[FONT=comic sans ms]You can see those boundaries and if you want to feel those boundaries you can put your finger in and see that this is the boundary,[/FONT]
[FONT=comic sans ms]this is the boundary, this inner surface of the cap when it is fitted there is also a boundary.[/FONT]
[FONT=comic sans ms]But I can define a different system saying that look contents of this bottle without the cap.[/FONT]
[FONT=comic sans ms]The boundaries are the inner surface of this bottle and the closing boundary is the top surface of this bottle.[/FONT]
[FONT=comic sans ms]Now there is no surface here - I can put my finger through it, but you can imagine a closing surface out there at the opening of this bottle.[/FONT]
[FONT=comic sans ms]So this is a boundary - illustration of a boundary which is defined geometrically - there is a circular edge here -[/FONT]
[FONT=comic sans ms]cover that up with an imaginary surface and that happens to be our boundary.[/FONT]
[FONT=comic sans ms]I can define another system.[/FONT]
[FONT=comic sans ms]For example I can define only the water in this bottle as my system.[/FONT]
[FONT=comic sans ms]Not earlier as we defined the complete contents of this bottle.[/FONT]
[FONT=comic sans ms]Let me close it so that I don't spill water and let us say that if I hold it reasonably steadily there is a surface -[/FONT]
[FONT=comic sans ms]top surface of the water which would be our boundary and the other boundaries are the inner surface of the bottle and the bottom which are in contact with the water.[/FONT]
[FONT=comic sans ms]Whereas this top surface top inner surface of the bottle, the cap, etc., are not part of our system boundaries at all.[/FONT]
[FONT=comic sans ms]Our system boundaries are the side walls, the bottom walls and the surface of the water.[/FONT]
[FONT=comic sans ms]Remember that here the surface of the water although physically defined, is flexible.[/FONT]
[FONT=comic sans ms]If I tilt it, it changes it's location, it changes it's size.[/FONT]
[FONT=comic sans ms]And also the side boundaries some of them shrink some of them expand or get extended.[/FONT]
[FONT=comic sans ms]So this gives you an illustration of how flexible the idea of boundaries will be.[/FONT]
[FONT=comic sans ms]It is even possible to define boundaries purely imaginary - in our imagination.[/FONT]
[FONT=comic sans ms]For example I can say consider in front of me an imaginary box 10 centimetres this way 10 centimetres this way 10 centimetres this way.[/FONT]
[FONT=comic sans ms]So we have a box, a cubic box 10 cm by 10 cm by 10 cm which is in front of me.[/FONT]
[FONT=comic sans ms]I can't see it, but I can imagine it start from say here,[/FONT]
[FONT=comic sans ms]go 10 cm this way 10 cm this way that will define a square of 10cm by 10cm consider a height of 10 cm and you have a cube of 10 cm by 10 cm by 10 cm.[/FONT]
[FONT=comic sans ms]Ok, so that becomes my system.[/FONT]
[FONT=comic sans ms]Here I cannot show the boundaries but on a drawing or on a sketch I can show now that my system consists of a cubic region 10 cm by 10 cm by 10 cm.[/FONT]
[FONT=comic sans ms]The other edges would also be the there so we can draw all 6 surfaces and 12 edges so this could be my system, a sort of an abstract system,[/FONT]
[FONT=comic sans ms]but sometimes such abstract systems are also useful.[/FONT]
[FONT=comic sans ms]We have already seen the contents of a bottle, I can sketch it, put a cap and say this is my system.[/FONT]
[FONT=comic sans ms]Just to emphasise the boundaries I will overlay them with dashed or dotted lines.[/FONT]
[FONT=comic sans ms]So now this is my system.[/FONT]
[FONT=comic sans ms]Now the important thing to remember is, system is always defined by its boundaries and because all the boundaries are defined one characteristic or the primary characteristic any thermodynamic system will have is it volume.[/FONT]
[FONT=comic sans ms]So any system, remember, must have associated with it one property or one characteristic called volume.[/FONT]
[FONT=comic sans ms]It may have other characteristics, it may have some mass, it may have some energy, it may have some electric charge.[/FONT]
[FONT=comic sans ms]That's ok, but any system must have a volume associated with it.[/FONT]
[FONT=comic sans ms]It could be a system as small as a small droplet of water or a small bubble of vapour or it could be a large system saying[/FONT]
[FONT=comic sans ms]whatever is contained in this house or in this room.[/FONT]
[FONT=comic sans ms]we will look at other properties of systems later.[/FONT]
[FONT=comic sans ms]In fact, what is meant by a property is something which we have yet to define.[/FONT]
[FONT=comic sans ms]In this course we will find that we will talk about certain concepts, certain ideas, but define them slightly later.[/FONT]
[FONT=comic sans ms]That will usually happen.
[/FONT]

 

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Lecture 2: Basic Ideas and Definitions > System Boundaries

Lecture 2: Basic Ideas and Definitions > System Boundaries

Basic Ideas and Definitions 2

[FONT=comic sans ms]
[/FONT][FONT=comic sans ms]Now, we have seen right from our introductory video that thermodynamics studies interactions between systems.[/FONT]
[FONT=comic sans ms]Notice the plural: 'systems'. And we have said the interactions are energy interactions.[/FONT]
[FONT=comic sans ms]We will again come to interactions later, but let's say the interactions is something like a transaction.[/FONT]
[FONT=comic sans ms]Just the way we have we go to a bank and withdraw money from our account that's a financial transaction, its monetary transaction.[/FONT]
[FONT=comic sans ms]It's a give and take something comes out of the account into your hand, or if you deposit money[/FONT]
[FONT=comic sans ms]something from your pocket goes into your bank in your account.[/FONT]
[FONT=comic sans ms]So interaction is like a transaction; that was a monetary interaction and here we will be talking about energy interactions.[/FONT]
[FONT=comic sans ms]And because interactions involves at least two systems.[/FONT]
[FONT=comic sans ms]Interaction is always between two systems and is across the boundary separating them.[/FONT]
[FONT=comic sans ms]Hence it is necessary for us to be clear about - the idea of the two interacting systems and the boundary separating them.[/FONT]
[FONT=comic sans ms]A general model could be something like this - we have one system, we have another system nearby,[/FONT]
[FONT=comic sans ms]and we have a boundary separating them. A common boundary.[/FONT]
[FONT=comic sans ms]So we can say, this is the system which is under study. Let's called it system A.[/FONT]
[FONT=comic sans ms]This is the second system with which the first system, system A is interacting. Let's called it system B.[/FONT]
[FONT=comic sans ms]And this is the boundary separating A and B, system A and system B.[/FONT]
[FONT=comic sans ms]An interactions of energy take place between the two systems across this boundary.[/FONT]
[FONT=comic sans ms]In fact, system A will be a proper thermodynamic system. System B will also be a proper thermodynamic system.[/FONT]
[FONT=comic sans ms]However, quite often one of the two systems say system A is the system of primary interest.[/FONT]
[FONT=comic sans ms]In which case we may simply call it the system. This could be then the secondary system.[/FONT]
[FONT=comic sans ms]The primary system and the secondary system.[/FONT]
[FONT=comic sans ms]So we may call the two systems as - system A or system B. A system of primary interest or simply the system.[/FONT]
[FONT=comic sans ms]System B could be the secondary system, but quite often the secondary system is given the name - surroundings.[/FONT]
[FONT=comic sans ms]Remember that although quite often we will be talking of the system and its surroundings.[/FONT]
[FONT=comic sans ms]Remember that the surroundings is also a thermodynamics system in its own right.[/FONT]
[FONT=comic sans ms]It should also be a properly defined thermodynamic system. It should also have all its boundaries properly defined.[/FONT]
[FONT=comic sans ms]However, quite often we come across situations - where our primary system is of importance to us - we called it the system.[/FONT]
[FONT=comic sans ms]Whereas, the real surroundings say suppose I am the system - a surrounding is this room in particular the air in this room.[/FONT]
[FONT=comic sans ms]So, that air I can consider it a large system.[/FONT]
[FONT=comic sans ms]And during my interaction with the air in the few minutes that I'm going to sit here[/FONT]
[FONT=comic sans ms]and talk and make some gestures and write something.[/FONT]
[FONT=comic sans ms]The situation in that air is not going to significantly change, it will change.[/FONT]
[FONT=comic sans ms]There will be some effect but there will be a minor effect.[/FONT]
[FONT=comic sans ms]Such as surrounding system is quite often known as an environment.[/FONT]
[FONT=comic sans ms]These are the just different words use in the textbooks of thermodynamics and when we discuss thermodynamics.[/FONT]
[FONT=comic sans ms]But, we should remember that - the surroundings or the environment is as much a properly defined thermodynamic system[/FONT]
[FONT=comic sans ms]as our system itself or the primary system itself. We can stop here.[/FONT]

 

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Lecture 2: Basic Ideas and Definitions > Classification of Systems

Lecture 2: Basic Ideas and Definitions > Classification of Systems

Classification of Systems

[FONT=comic sans ms]We will now look at some simple classification of systems.[/FONT]
[FONT=comic sans ms]This depends on essentially the type of boundaries that the system has, the behaviour of boundaries.[/FONT]
[FONT=comic sans ms]In particular, what are the interactions which are possible across the boundaries,[/FONT]
[FONT=comic sans ms]and the main interaction which we can look at for classification is the mass flow.[/FONT]
[FONT=comic sans ms]For example, let's consider movement of mass across system boundaries, if this is possible then we call the system an open system.[/FONT]
[FONT=comic sans ms]However, if the flow of mass, or movement of mass is not possible, or is prevented then we call the system a closed system.[/FONT]
[FONT=comic sans ms]This is the basic classification of thermodynamic system, it depends on the type of boundaries that it has.[/FONT]
[FONT=comic sans ms]If a system has a part of the boundary at least across which mass can flow in and flow out, we will call it an open system.[/FONT]
[FONT=comic sans ms]If mass flow is not possible, if it is prevented by some reason or by some technique, then we will call it a closed system.[/FONT]
[FONT=comic sans ms]Take for example again this water bottle, now if it is sealed and the cap of the bottle is closed tight so that it is leak proof[/FONT]
[FONT=comic sans ms]then we say that - if my system is whatever is contained in the bottle - air and water,[/FONT]
[FONT=comic sans ms]boundaries are the inner surfaces of the bottle, then it is a closed system - no mass can come in, no mass can go out.[/FONT]
[FONT=comic sans ms]However, it is possible that the water is cold, my hands are warm, water is at 27°C,[/FONT]
[FONT=comic sans ms]my hands are at 36°C, is a temperature difference, so heat may flow from my hands to the water in the bottle heating it up,[/FONT]
[FONT=comic sans ms]that's an energy transaction. We will study these in detail later.[/FONT]
[FONT=comic sans ms]So, although it's a close system, although mass flow is prevented, it's possible that energy transaction does take place,[/FONT]
[FONT=comic sans ms]but it's a closed system because mass can not come in and go out.[/FONT]
[FONT=comic sans ms]However, if a part of the boundary is open like this, and water can come in, or go out I can drink water out of it,[/FONT]
[FONT=comic sans ms]then during that process, and even now, the system as defined,[/FONT]
[FONT=comic sans ms]but now with this top surface as an imaginary surface, is an open thermodynamic system.[/FONT]
[FONT=comic sans ms]You should understand this basic difference between closed thermodynamics systems and open thermodynamics systems,[/FONT]
[FONT=comic sans ms]and should remember that energy transfer in any form is possible in either case, whether the system is closed or the system is open.[/FONT]
[FONT=comic sans ms]However, it is possible that the boundaries of a system are such that mass flow is prevented and energy flow is also prevented.[/FONT]
[FONT=comic sans ms]In such a case, we call the system an isolated system, no energy transactions, no mass exchange.[/FONT]
[FONT=comic sans ms]Closed systems are important because they are simple to study, we don't have to worry about mass coming in and going out.[/FONT]
[FONT=comic sans ms]The laws of thermodynamics will be derived, and we will study them for closed systems,[/FONT]
[FONT=comic sans ms]and then we will transform them so that they are applicable to open systems.[/FONT]
[FONT=comic sans ms]So henceforth till about may be halfway or slightly more than halfway through the course,[/FONT]
[FONT=comic sans ms]we would essentially be looking at closed thermodynamic systems, and then we will say[/FONT]
[FONT=comic sans ms]that look now we have studied enough of thermodynamics as pertaining to closed systems,[/FONT]
[FONT=comic sans ms]let's now look at open systems and convert these laws into appropriate forms applicable to open thermodynamics systems.[/FONT]

 

[P O U R I A]

Lecture 2: Basic Ideas and Definitions > System Illustrations

Lecture 2: Basic Ideas and Definitions > System Illustrations

Illustrations 1​

[LEFT][FONT=comic sans ms]
We now look at some illustrations of thermodynamics systems,[/FONT]
[FONT=comic sans ms]we will see a real physical situation and then look at the way we abstract it and come to a final system figure from the point of view of thermodynamics.[/FONT]
[FONT=comic sans ms]The first illustration we have here is water inside this bottle,[/FONT]
[FONT=comic sans ms]so here we have the photograph of the water inside this bottle and the first thing we do is mark the boundary of the water, you see it in black here[/FONT]
[FONT=comic sans ms]once you mark the boundary of the water the region of interest then we can neglect or forget the details of the bottle,[/FONT]
[FONT=comic sans ms]the shape, the extraneous things, so this is the boundary of our system and to emphasise that,[/FONT]
[FONT=comic sans ms]this itself is the boundary of the system, we will generally inlay it the exact boundary with a dotted line,[/FONT]
[FONT=comic sans ms]so our system that is water in the bottle is whatever is contained inside this dotted boundary line.[/FONT]
[FONT=comic sans ms]Another illustration of a system is air inside the tyre of a car,[/FONT]
[FONT=comic sans ms]so here we have the picture with all the clutter the wheel, the connecting bolts, the tyre,[/FONT]
[FONT=comic sans ms]you don't see the tube inside, the structure of the car part of the mudguard,[/FONT]
[FONT=comic sans ms]okay the first thing will do is mark the boundary and we can imagine that the air will be in the form of a ring and or a torus and here we have the inner radius of the torus and this is the outer surface of the torus.[/FONT]
[FONT=comic sans ms]Once we do that we can now concentrate on the boundary and to get rid of the confusion,[/FONT]
[FONT=comic sans ms]we inlay it with dotted lines so you see two sort of circular dotted lines whatever is the toroidal zone,[/FONT]
[FONT=comic sans ms]ring like zone in between is our system, it contains the air which is in this car tyre,[/FONT]
[FONT=comic sans ms]so here we have a tank and let us say that the contents of the tank are going to be part of our system,[/FONT]
[FONT=comic sans ms]although the tank is meant for nitrogen it could contain anything,[/FONT]
[FONT=comic sans ms]so the first thing we do is draw the outline of the tank.[/FONT]
[FONT=comic sans ms]the moment we draw the outline of the tank we have made the primary boundary we can forget about the details of the tank and so this is the system boundary[/FONT]
[FONT=comic sans ms]and to emphasise what the system boundary really is we show it by a dotted line.[/FONT]
[FONT=comic sans ms]Again here we notice that we have a passage here and another passage here one of them could be an inflow passage one of them could be an outflow passage[/FONT]
[FONT=comic sans ms]and if the two passages are not closed they are open it will be an open system if they are closed then our system will be a closed system.[/FONT]
[FONT=comic sans ms]Here is the illustration of a syringe.[/FONT]
[FONT=comic sans ms]It is made up of essentially two main components, a cylinder and a piston[/FONT]
[FONT=comic sans ms]and this is the part where the medicine or whatever is to be injected can be located[/FONT]
[FONT=comic sans ms]and through this spout and through a needle which is connected to it, it can be injected into a human, animal or whatever it is.[/FONT]
[FONT=comic sans ms]Suppose the/ just now it contains air but it could contain anything else so suppose the air inside this syringe is going to be our system.[/FONT]
[FONT=comic sans ms]So first what we have done that we have laid out the appropriate boundaries and once you have laid out the appropriate boundaries the actual physical detail of the syringe we can neglect[/FONT]
[FONT=comic sans ms]so what we see is this cylinder, the hollow part and the piston which we can push in to inject whatever is inside through the spout[/FONT]
[FONT=comic sans ms]since the content say in this particular case air inside this cylinder is going to be our system,[/FONT]
[FONT=comic sans ms]we will show it by a dotted line so as not to get confused by the other things and now here you will notice something which we will come across in thermodynamics quite often[/FONT]
[FONT=comic sans ms]we have a cylinder and a piston and whatever is contained inside the cylinder is our thermodynamic system.[/FONT]
[FONT=comic sans ms]Another illustration which leads to a cylinder piston type of arrangement is a foot pump used to inflate bicycle tyres or sometimes even small car tyres[/FONT]
[FONT=comic sans ms]so here you see the structure, the pressure gauge, the rod of the piston, this is a cylinder in which the air gets compressed,[/FONT]
[FONT=comic sans ms]and this is the connecting tube the other end of which would be connected to the tyre is a lot of clutter.[/FONT]
[FONT=comic sans ms]So the first thing we'll do is note the boundaries of the components which are of interest,[/FONT]
[FONT=comic sans ms]we will see them here sketched in black once you do that the next step is ofcourse to remove all the clutter and look at the boundaries[/FONT]
[FONT=comic sans ms]and again there is some confusion so if our system is the air inside this particular foot pump or the cylinder of the foot pump we lay it out with dotted lines[/FONT]
[FONT=comic sans ms]so whatever is inside the dotted line here is the our system the air inside this.[/FONT]
[FONT=comic sans ms]Another illustration is that of a water pump,[/FONT]
[FONT=comic sans ms]here you will see in a laboratory situation is a centrifugal water pump,[/FONT]
[FONT=comic sans ms]it is driven by a motor which is inside this safety shield,[/FONT]
[FONT=comic sans ms]this is the inlet pipe through which the pump sucks in water,[/FONT]
[FONT=comic sans ms]this is the exhaust pipe through which the pump throws out water at a high pressure.[/FONT]
[FONT=comic sans ms]So the first thing will do is to sketch out the boundaries of the system involved and you will see here the boundaries sketched out in black,[/FONT]
[FONT=comic sans ms]once you do that next thing is to look at the boundary itself and we have a region which could be our system,[/FONT]
[FONT=comic sans ms]but then let us say that the water inside this pump is going to be our system so we lay it out in the dotted line[/FONT]
[FONT=comic sans ms]so whatever is inside this dotted line that is going to be water and that is our thermodynamic system.[/FONT]
[FONT=comic sans ms]We will notice that the motor part in which there is no water present is not part of our thermodynamic system[/FONT]
[FONT=comic sans ms]and hence it's not included in the dotted line,[/FONT]
[FONT=comic sans ms]will also notice that water can flow in through this inlet duct and water can flow out through this exhaust duct so this is an illustration of an open thermodynamic system.[/FONT][/LEFT]

 

[P O U R I A]

Lecture 2: Basic Ideas and Definitions > System Illustrations

Lecture 2: Basic Ideas and Definitions > System Illustrations

Illustrations 2

​

[LEFT][FONT=comic sans ms]
[/FONT]
[FONT=comic sans ms]Welcome back. Let us consider illustrations of some real life systems.[/FONT]
[FONT=comic sans ms]Here you have a photograph of a power plant. There are a number of units in this station.[/FONT]
[FONT=comic sans ms]But, in the forefront you will see one thermal power plant. It takes in coal, produces electricity.[/FONT]
[FONT=comic sans ms]It takes in cooling water, slightly warmer water is thrown away, and through the stacks you throw away flue gases,[/FONT]
[FONT=comic sans ms]the burned product, carbon dioxide and other stuff.[/FONT]
[FONT=comic sans ms]We may consider the whole power plant as our system. It will be an open system.[/FONT]
[FONT=comic sans ms]Because it takes in coal; throws out through the chimneys an exhaust.[/FONT]
[FONT=comic sans ms]Because it is coal it may contain some ash which doesn't get burnt, so ash is also discharged.[/FONT]
[FONT=comic sans ms]Then you have cooling water going in and cooling water going out.[/FONT]
[FONT=comic sans ms]And then of course you have energy output as electricity.[/FONT]
[FONT=comic sans ms]This whole thing can be considered to be a power plant.[/FONT]
[FONT=comic sans ms]And we can apply our principles of thermodynamics to such a large system.[/FONT]
[FONT=comic sans ms]However, it is also possible to consider components of the power plants.[/FONT]
[FONT=comic sans ms]For example, the main subsystems in the power plant are - the boiler. Sometimes called the steam generator.[/FONT]
[FONT=comic sans ms]Then steam goes to a turbine. From turbine low pressure steam goes to condenser, where cooling water comes in.[/FONT]
[FONT=comic sans ms]So, this is the cooling water circuit. Steam condenses, the condensate is pumped back into the boiler.[/FONT]
[FONT=comic sans ms]This is a very simplified form of our power plant.[/FONT]
[FONT=comic sans ms]Now, the turbine produces mechanical power which is passed on to the generator.[/FONT]
[FONT=comic sans ms]The generator creates electricity which is the output. Final output of the plant.[/FONT]
[FONT=comic sans ms]Apart from this - you have in the boiler, a furnace.[/FONT]
[FONT=comic sans ms]In which we put in coal, air also goes in it is required for combustion.[/FONT]
[FONT=comic sans ms]Ash discharged at the bottom and flue gases at the top.[/FONT]
[FONT=comic sans ms]Now, this is the approximate internal detail of the earlier system which we saw.[/FONT]
[FONT=comic sans ms]So, I can put a dotted line around all this and that is essentially the system we saw few minutes ago.[/FONT]
[FONT=comic sans ms]But, it is also possible to considered sub-systems. For example, this is my turbine system.[/FONT]
[FONT=comic sans ms]And I can apply my laws of thermodynamics to this smaller system which consists of the turbine.[/FONT]
[FONT=comic sans ms]One inlet, one exist so it's an open system.[/FONT]
[FONT=comic sans ms]Similarly, we can apply the laws of thermodynamics to the condenser as a system, or to the pump as a system.[/FONT]
[FONT=comic sans ms]When it comes to boiler. We can consider just the water holding and water flowing part of the boiler.[/FONT]
[FONT=comic sans ms]Which converts water into steam as our system, or you could have the furnace which handles coal burns it with oxygen from the air.[/FONT]
[FONT=comic sans ms]And transfer the energy liberated as heat to the water in the boiler that could be a system.[/FONT]
[FONT=comic sans ms]This is just to illustrate that the choice of a system and it boundaries is our choice.[/FONT]
[FONT=comic sans ms]If we want to look at something at a gross level, overall level. We can consider the whole plant as a system.[/FONT]
[FONT=comic sans ms]If you want to consider sub components study their characteristic.[/FONT]
[FONT=comic sans ms]For example, we can have a turbine as a system to study the details of the turbine.[/FONT]
[FONT=comic sans ms]We can even go to the internals of the turbine and there are various stages.[/FONT]
[FONT=comic sans ms]Typical turbine will have anywhere between 10 and 20 stages.[/FONT]
[FONT=comic sans ms]Stack like slices of a loaf of bread, each stage can be considered as a smaller thermodynamic system.[/FONT]
[FONT=comic sans ms]And if you really want to go into details. A stage consists of a few dozen to a few hundred blades.[/FONT]
[FONT=comic sans ms]And the space between two blades can also be considered to be a properly defined thermodynamic system.[/FONT]
[FONT=comic sans ms]So the definition of a system depends on - what we want to study, and in what detail.[/FONT]
[FONT=comic sans ms]Now, here we see - a photograph of our earth taken from space.[/FONT]
[FONT=comic sans ms]Can we consider the whole of our earth as a system? And the answer is yes.[/FONT]
[FONT=comic sans ms]All that we have do is set up an appropriate boundary. We set up the boundary.[/FONT]
[FONT=comic sans ms]And we say - this is earth and its immediate surroundings - that is the atmosphere as system.our[/FONT]
[FONT=comic sans ms]What would be the neighbouring system across the boundary?[/FONT]
[FONT=comic sans ms]That would be the part of space, part of the solar system, just across our atmosphere.[/FONT]
[FONT=comic sans ms]We can apply and we do apply the laws of thermodynamics to our earth as a system.[/FONT]
[FONT=comic sans ms]In fact, this is what of earth scientists and climate scientists do.[/FONT]
[FONT=comic sans ms]Finally, we ourselves - each one of us - is a thermodynamic system of the biological kind.[/FONT]
[FONT=comic sans ms]Of course we - anyone of us - as a thermodynamic system can be studied thermodynamically.[/FONT]
[FONT=comic sans ms]However, the structure and the internal working of such a system is so complex that in this course we will not make an attempt to study that.[/FONT]
[FONT=comic sans ms]Thank You.[/FONT][/LEFT]

 

[P O U R I A]

Lecture 2: Basic Ideas and Definitions > System Illustrations

Lecture 2: Basic Ideas and Definitions > System Illustrations

Illustrations 3​

[LEFT][FONT=comic sans ms]
[/FONT][FONT=comic sans ms]You would have noticed that many of our thermodynamic systems can be modded, can be approximated,[/FONT]
[FONT=comic sans ms]or abstracted as a cylinder piston arrangement, and because of that you will notice that a large number of illustrations[/FONT]
[FONT=comic sans ms]and figures in thermodynamics books will be that of a cylinder piston arrangement.[/FONT]
[FONT=comic sans ms]So if you see this arrangement you will find the cylinder inside the cylinder there will be a piston[/FONT]
[FONT=comic sans ms]and there will be a mechanism a piston rod, or a connecting rod which will move the piston up and down.[/FONT]
[FONT=comic sans ms]The cylinder will have a cover known as the cylinder head,[/FONT]
[FONT=comic sans ms]and typically let's assume that the cover will have two valves, and two ports in which the valves are located.[/FONT]
[FONT=comic sans ms]So let us say, this the inlet port, and this is the exhaust port.[/FONT]
[FONT=comic sans ms]This will be a typical cylinder piston arrangement.[/FONT]
[FONT=comic sans ms]This is the inlet port with the inlet valve, and this is the exhaust port, and this is the exhaust valve.[/FONT]
[FONT=comic sans ms]Our system will be, whatever is the fluid, which is enclosed inside this cylinder piston arrangement.[/FONT]
[FONT=comic sans ms]If both valves are closed then we have a closed thermodynamic system,[/FONT]
[FONT=comic sans ms]and our illustrations of the wheel, the water in the bottle, and a few others are illustrations of closed systems.[/FONT]
[FONT=comic sans ms]Whereas the syringe, the foot pump, which we saw in the previous set of illustrations are open systems[/FONT]
[FONT=comic sans ms]because if at least one valve, or one passage is open then we have an open system.[/FONT]
[FONT=comic sans ms]Remember that the cylinder piston arrangement is an illustration, or an approximation, or an abstraction of thermodynamics systems.[/FONT]
[FONT=comic sans ms]And as we proceed we will find will be able to approximate, not only closed systems and open systems by using this scheme,[/FONT]
[FONT=comic sans ms]but even in real life you will notice that, not only a syringe, but a similar arrangement of that of a gun,[/FONT]
[FONT=comic sans ms]or a cannon is that of a cylinder piston arrangement.[/FONT]
[FONT=comic sans ms]Not only that, you consider our lungs, to be an open thermodynamic system, we breath in air,[/FONT]
[FONT=comic sans ms]and we breath out whatever comes out of it, and there is a diaphragm which moves up and down,[/FONT]
[FONT=comic sans ms]so that something similar to a cylinder piston arrangement.[/FONT]
[FONT=comic sans ms]So as I breath in and as I breath out, that diaphragm is moving up and down,[/FONT]
[FONT=comic sans ms]so there is some sort of a natural cylinder piston arrangement even within us.[/FONT]
[FONT=comic sans ms]
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[P O U R I A]

Lecture 2: Basic Ideas and Definitions > The State of a System

Lecture 2: Basic Ideas and Definitions > The State of a System

The State of a System, Properties​

[/FONT][LEFT][FONT=comic sans ms]We now come to a stage where we have to define what we call the state of a system,
this is required because in thermodynamics anything we study will typically be of this type.
We will have one system let's call it our primary system or system A.
We will have another system the secondary system or the environment let's call it system B.
Thermodynamics studies the interaction that is the give and take or the transfer of energy between these systems,
and because of this interaction there is a change in system A and there will also be some corresponding change in system B.
We have to relate this change to the interaction and for this we will have to not only quantify the interactions properly,
but will have to quantify the change in the behavior of a system,
and to decide on this change we say that we study and we observe the state of a system
so that we can note and study the change in the state.
An illustration not necessarily thermodynamic a simple illustration of an interaction is a financial interaction.
I go to a stall, I want a piece of cake so I ask the serviceman for a piece of cake,
he gives me a piece of cake and I take out of my pocket the appropriate amount of money, cash and give it to him
so there is a cash transaction from me to the serviceman and there is a material transaction between the serviceman and me.
So because of this, the state of me changes earlier may be I had so much money with me, say 80 rupees,
I gave him 10 rupees so my money in my pocket is now 70 rupees.
So there is a change in the state of myself in terms of the money in my pocket.
How do I define the state of a system?
Let's say this is our system, could be anything water in the bottle, gas in a cylinder. We do two things to define the state of a system,
we have to do, first make a list of relevant characteristics of a system.
For example if we consider the system to be gas in a cylinder, closed cylinder,
so a closed system and we may say that look mass of the gas is one relevant characteristic,
pressure of the gas p is another relevant characteristic, and the temperature of the gas is the third relevant characteristic.
It need not be three could be as small as one it could be as many as there is no upper limit.
More complicated and more complex a system, we will have a large number of these characteristics.
Thermodynamics does not directly restrict the number of characteristics or relevant characteristics
that a system may have, later on we will see what are the appropriate numbers.
The word relevant is important and it is only experience which tells us what is relevant or not.
For example, if this is a rigid cylinder and if there are going to be no significant variations in temperature and pressure,
we will say that the volume is unlikely to change and hence volume may not be listed as a relevant characteristic in this particular case.
So after making a list of relevant characteristics the second operation is to quantify,
by quantification we mean measure or by hook or by crook somehow put a value on each of these relevant characteristics.
For example, we may measure the mass of the gas as say 20 kilograms,
we may measure the pressure using a pressure gauge connected to the cylinder as say 20 bar
and we may determine that the temperature is 14 degrees C, perhaps a cold winter day.
So when will do this when we have a list of a relevant characteristics and the quantity or the numbers associated with them
we say that we have defined the state of our system and our system is this gas in the cylinder, mass 20 kg, pressure 20 bar, temperature 14 degree C.
So we can say our system is gas symbolism could be like this, mass 20 kg, pressure 20 bar, temperature 14 degree C.
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[P O U R I A]

Lecture 2: Basic Ideas and Definitions > Microscopic, Macroscopic

Lecture 2: Basic Ideas and Definitions > Microscopic, Macroscopic

Microscopic, Macroscopic

Let us consider different ways to describe a system.
Because each property is a relevant characteristics which describes the system,
but the way we describe the system depends on the approach we have.
For example, our viewpoint or our approach could be microscopic as against macroscopic.
So let's look at the microscopic approach.
A microscopic approach is the typical approach of a physicist or a chemist.
Here we assume that a system is made up of a collection of a large number N of particles.
What is the order of N?
Very large, 10 raised to 20, 10 raised to 25, of the order of the Avogadro number
and each of these particles is moving randomly during the course of a system.
Particle may move from one part of the system to any other part of the system.
So each particle will have a position, and will have a velocity, and the position of each particle will be a function of time.
The velocity of each particle will also be a function of time, and that means suppose there are a large number N of particles,
we will have to specify N positions and N velocity vectors each one as a function of time,
and consequently this leads to a large number of pieces of information, and it's not so easy to handle.
So hence, a consequence of this - some type of averaging is used,
and this leads to a statistical approach leads to statistical thermodynamics, statistical mechanics, this is the statistical approach.
We are engineers and engineers in particular mechanical engineers, generally do not need to use the microscopic approach.
We are very happy to use the macroscopic approach. Our viewpoint is macroscopic and not microscope.
Here, we will consider each system to be a continuum,
and the advantage of this considering each system to be a continuum is that,
we need to have only a few properties sometimes as few as 2 or 3 sometimes perhaps as many as a dozen,
but never more than a reasonably small number,
and because of a few properties we have a small number of variables and hence a small number of equations.
Both of which are advantageous for proceeding with the solution of a problem.
So small number of variables means a small number of properties,
and small number of equations means a few laws, and other relations that we have to work with.
This approach is also known as the phenomenological approach.
Because here we are going to study the phenomena which take place,
generalise those phenomena as our laws of thermodynamics, it is also known as the classical approach

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[P O U R I A]

Lecture 2: Basic Ideas and Definitions > Properties

Lecture 2: Basic Ideas and Definitions > Properties

Properties 1

[FONT=comic sans ms]
[/FONT]
[FONT=comic sans ms]Let us now look at the way properties are classified.[/FONT]
[FONT=comic sans ms]One way to classify properties in thermodynamics is to look at the origin of these properties.[/FONT]
[FONT=comic sans ms]For example, some properties would be primitive properties.[/FONT]
[FONT=comic sans ms]Primitive properties are defined elsewhere and used in thermodynamics.[/FONT]
[FONT=comic sans ms]For example from geometry we use volume defined in geometry; mass, velocity defined in mechanics,[/FONT]
[FONT=comic sans ms]kinetic energy gravitational potential energy also defined in mechanics.[/FONT]
[FONT=comic sans ms]So these are the properties which are defined by other branches of physics[/FONT]
[FONT=comic sans ms]and are absorbed in thermodynamics with all their characteristics as defined in other branches of physics.[/FONT]
[FONT=comic sans ms]A very common property which will be using is pressure, force per unit area which is defined in mechanics.[/FONT]
[FONT=comic sans ms]Then comes the most important set of properties.[/FONT]
[FONT=comic sans ms]Let's call them basic thermodynamic properties. These are based on the laws of thermodynamics.[/FONT]
[FONT=comic sans ms]Since, we are going to study basically three laws of thermodynamics.[/FONT]
[FONT=comic sans ms]The three laws will give us three basic thermodynamic properties.[/FONT]
[FONT=comic sans ms]For example, the zeroth law will help us define a thermodynamic property called temperature.[/FONT]
[FONT=comic sans ms]The first law will help us define a thermodynamic property called energy[/FONT]
[FONT=comic sans ms]and from which because energy is an idea which is common to many other branches of physics.[/FONT]
[FONT=comic sans ms]We will extract a component which is thermal energy.[/FONT]
[FONT=comic sans ms]And finally the second law - which will help us defined the third and a very important thermodynamic property called entropy.[/FONT]
[FONT=comic sans ms]We also have a third type of property known as a derived property. Derived properties are useful short forms.[/FONT]
[FONT=comic sans ms]These are the combination of other properties.[/FONT]
[FONT=comic sans ms]One very common combination is the following - we come across this combination U+pV,[/FONT]
[FONT=comic sans ms]the thermal energy, and pressure, volume, product added together.[/FONT]
[FONT=comic sans ms]This combination turns up so often in thermodynamics that we give it a short form and another name enthalpy.[/FONT]
[FONT=comic sans ms]A symbol often used is H. The name is enthalpy.[/FONT]
[FONT=comic sans ms]There are other properties which will come across later as derived properties.[/FONT]
[FONT=comic sans ms]For example, the Gibbs function, the Helmholtz function.[/FONT]
[FONT=comic sans ms]Another illustration of a derived property are compressibility or expansion coefficient.[/FONT]
[FONT=comic sans ms]For example, for a fluid, this is known as an Alpha [α] and this is known as the isobaric thermal expansion coefficient and there are many others.[/FONT]
[FONT=comic sans ms]
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[P O U R I A]

Lecture 2: Basic Ideas and Definitions > Properties

Lecture 2: Basic Ideas and Definitions > Properties

Properties 2

Another way to classify properties are to classify them as extensive or intensive, and of course there is a somewhat related called specific property.
So these are the three adjectives which can be associated with properties.
First, let us look at the extensive and intensive.
We consider a system, let us say this is our system.
Let's say system A, and let us say it has some property let us call that property of this system X.
It could be pressure, it could be volume, it could be energy some property let's call that property X.
Now let us imagine, a partitioning of this system.
That means imagine a surface separating the system into two parts equal or unequal.
Let say this is part 1 let us say this is part 2, parts 1 and 2 totally make up a system A.
Since this surface is properly defined.
1 by itself is a thermodynamics system; 2 by itself is another thermodynamic system.
And system 1, system 2 when combined together give us system A.
This property X when measured for system A has the value X
but when measured for this part of the system, system 1 let the value of the property be X1.
And when it is measured for this part of the system let the value of the property be X2.
Now using X, X1 and X2 let us define extensive and intensive as follows.
If X turns out to be X1+X2 then we say that X is an extensive property. Because it depends on the extent.
If on the other hand, X turns out to be equal to X1 and equal to X2 if all three are equal then we say that X is an intensive property.
Illustration of an extensive property would be mass, volume, energy.
Typical illustrations of intensive properties are temperature, pressure, say density.
Let us now look at, what is meant by a specific property.
Specific property is defined as follows, If X is an extensive property of a system then X/m where m is the mass of the system is defined
usually given the symbol small x or a lower case x and x is then known as the specific property, property related to x.
For example, a system has mass m then V volume would be an extensive property but V/m which is specific volume this will be a specific property.
Similarly we could take energy, enthalpy, entropy these are extensive properties,
but energy per unit mass or specific energy, enthalpy per unit mass or specific enthalpy,
and entropy per unit mass which is specific entropy are all specific properties.

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[P O U R I A]

Lecture 3: Thermodynamic State Space > Properties and State

Lecture 3: Thermodynamic State Space > Properties and State

Properties and State

[/FONT][FONT=comic sans ms]
[/FONT]
[FONT=comic sans ms]We have seen that - the thermodynamics properties of a system define its state.[/FONT]
[FONT=comic sans ms]So, the questions which come to mind are - how many properties are needed to define the state?[/FONT]
[FONT=comic sans ms]And the second question which immediately comes to mind is which ones.[/FONT]
[FONT=comic sans ms]Actually thermodynamics tells us something about these, but does not really give a definitive answer.[/FONT]
[FONT=comic sans ms]It doesn't say four properties, or it doesn't say pressure, volume, temperature.[/FONT]
[FONT=comic sans ms]However, there are in thermodynamics what are known as state postulates, which tell us something about[/FONT]
[FONT=comic sans ms]the number of properties not necessarily about which ones, which ones is to a very very large extent our choice, our convenience.[/FONT]
[FONT=comic sans ms]Now, since we have used the word postulates.[/FONT]
[FONT=comic sans ms]Let us spend some time on these words.[/FONT]
[FONT=comic sans ms]Postulates, premises, assumptions and laws.[/FONT]
[FONT=comic sans ms]Not all of these are related they are differences.[/FONT]
[FONT=comic sans ms]But, we will be coming across these words laws, assumptions, premises,[/FONT]
[FONT=comic sans ms]and postulates reasonably often in our study of thermodynamics.[/FONT]
[FONT=comic sans ms]Actually there is hardly any significant difference between postulates, premises, and laws.[/FONT]
[FONT=comic sans ms]Particularly between postulates and laws.[/FONT]
[FONT=comic sans ms]These are our understanding of the way nature behaves.[/FONT]
[FONT=comic sans ms]We observe nature all science does is that it observes nature and by pattern matching, generalisation, repeated observation[/FONT]
[FONT=comic sans ms]so called inductive logic comes to a conclusion that - this is the way nature behaves.[/FONT]
[FONT=comic sans ms]And this behaviour when written down formally becomes a postulate or a law.[/FONT]
[FONT=comic sans ms]Sometimes called a premise, but the main name for these things it postulates or laws.[/FONT]
[FONT=comic sans ms]In thermodynamics, there will be a number of postulates or laws that we will come about.[/FONT]
[FONT=comic sans ms]However there are only a few of those particularly three.[/FONT]
[FONT=comic sans ms]The zeroth law, the first law, and the second law have been given formerly the status of a law.[/FONT]
[FONT=comic sans ms]The other things we called a postulate. For example, the state postulate.[/FONT]
[FONT=comic sans ms]A premise or an assumption is somewhat different. Now this is something which we make to simplify the study.[/FONT]
[FONT=comic sans ms]Sometimes to restrict ourselves, so we don't have to worry about too many things too soon.[/FONT]
[FONT=comic sans ms]The first postulate let me call it, state postulate one.[/FONT]
[FONT=comic sans ms]Is that, the state of any thermodynamic system can be defined using primitive properties only.[/FONT]
[FONT=comic sans ms]This means that - although we talk about quantities like thermal energy, temperature, entropy.[/FONT]
[FONT=comic sans ms]It is not necessary for us to define the state of a system using any of these.[/FONT]
[FONT=comic sans ms]State of a system can always be defined using primitive properties.[/FONT]
[FONT=comic sans ms]Like mass, volume, pressure, velocity, location and things like that.[/FONT]
[FONT=comic sans ms]Now, this is something which is a postulate, so we don't have a derivation for this.[/FONT]
[FONT=comic sans ms]But, the way we have observed nature and thermodynamics systems to behave it has been found to be true, no contradiction as of now.[/FONT]
[FONT=comic sans ms]So, let's called this state postulate one.[/FONT]
[FONT=comic sans ms]For simplifying our study of thermodynamics. And to restrict ourselves to the classical domain of thermodynamics.[/FONT]
[FONT=comic sans ms]We will be making the following assumptions, these are our premises.[/FONT]
[FONT=comic sans ms]Will be making many of these a few which immediately are of interest to us that any system is part of a continuum.[/FONT]
[FONT=comic sans ms]So no distinct effects. No quantization.[/FONT]
[FONT=comic sans ms]Second assumption which we will make is that - there are no scale effects.[/FONT]
[FONT=comic sans ms]That means, whatever is true for a small system will be true for a smaller system,[/FONT]
[FONT=comic sans ms]will be true for a larger system, and will be true for a still larger system.[/FONT]
[FONT=comic sans ms]The third assumption which we will make for this course is that - there are no quantum effects.[/FONT]
[FONT=comic sans ms]That means any property varies continuously.[/FONT]
[FONT=comic sans ms]And the fourth assumption we will make is that - there are no relativistic effects.[/FONT]
[FONT=comic sans ms]These four assumptions or premises will simplify things very significantly for us.[/FONT]
[FONT=comic sans ms]And henceforth we will not mentioned this assumptions again.[/FONT]
[FONT=comic sans ms]But we will use them as and when required.[/FONT]
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[P O U R I A]

Lecture 3: Thermodynamic State Space > Thermodynamic State Space

Lecture 3: Thermodynamic State Space > Thermodynamic State Space

Thermodynamic State Space

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[FONT=comic sans ms]Let us now see, how in thermodynamic, we visualize a state?[/FONT]
[FONT=comic sans ms]Let us take an illustration.[/FONT]
[FONT=comic sans ms]Let us say that we have a cylinder, and it contains a gas could be gas used for cooking,[/FONT]
[FONT=comic sans ms]it could be some gas used for welding, it could be oxygen used in a hospital.[/FONT]
[FONT=comic sans ms]Let us say that the relevant properties are pressure of the gas in the cylinder , temperature of the gas in the cylinder and mass of the gas.[/FONT]
[FONT=comic sans ms]And let us say that since it's a rigid cylinder, volume is unlikely to change[/FONT]
[FONT=comic sans ms]and hence we will not consider volume to be a significant variable or a relevant variable atleast you begin with.[/FONT]
[FONT=comic sans ms]And let us say that we have done measurements and said that after our measurement[/FONT]
[FONT=comic sans ms]the pressure has been measured to be 20 bar,temperature has been measured to be 14 degrees C[/FONT]
[FONT=comic sans ms]and mass has been measured to be 20 kg and our system is this gas.[/FONT]
[FONT=comic sans ms]One way of noting this down is our system and its state is gas, list of properties, quantification of property.[/FONT]
[FONT=comic sans ms]So P is 20 bar, T is 14 degree C and mass is 20 kg. Although this is the written description notice the similarity of these.[/FONT]
[FONT=comic sans ms]Now, look at it from the point of view of coordinate geometry.[/FONT]
[FONT=comic sans ms]Remember that there are three properties, so we could consider three dimensions.[/FONT]
[FONT=comic sans ms]Isn't this equivalent to saying that we have a point in three dimensional space represented by X=20, Y=14, Z=20 point in space.[/FONT]
[FONT=comic sans ms]And actually we can use this analogy to represent our system in three dimensional space.[/FONT]
[FONT=comic sans ms]We can nicely sketch the three dimensions like this.[/FONT]
[FONT=comic sans ms]Let us say here we represent pressure, here we will represent mass, and here we will represent temperature[/FONT]
[FONT=comic sans ms]The pressure is pressure in bar and our pressure is 20 bar, mass our mass is 20 kg, temperature, temperature is 14 degree C.[/FONT]
[FONT=comic sans ms]So, these are the three coordinates and using this three coordinates we can now locate our point in the three dimensional space.[/FONT]
[FONT=comic sans ms]Create a rectangular parallelepiped, so we will have our point somewhere here.[/FONT]
[FONT=comic sans ms]This point represents pressure of 20 bar, mass of 20 kg, temperature of 14 degree C.[/FONT]
[FONT=comic sans ms]This will be a representation of the state of our system.[/FONT]
[FONT=comic sans ms]Now remember that this is something like - in this particular case because there are three properties - three dimensional geometry.[/FONT]
[FONT=comic sans ms]The pressure is represented on one axis, the mass is represented on another axis[/FONT]
[FONT=comic sans ms]and temperature is represented on the third axis. So each coordinate represents a property.[/FONT]
[FONT=comic sans ms]So first thing we should realise is each property is represented by a coordinate then the geometric space will represent[/FONT]
[FONT=comic sans ms]the thermodynamic space and what is represented is the state of our system.[/FONT]
[FONT=comic sans ms]So one should remember and appreciate the analogy between the geometric space and the thermodynamic space.[/FONT]
[FONT=comic sans ms]This is known as thermodynamic state space.[/FONT]
[FONT=comic sans ms]In the thermodynamic state space each coordinate in this particular case pressure, mass, and temperature represents one thermodynamic property.[/FONT]
[FONT=comic sans ms]A state is represented by specified values of that property in this particular case pressure of 20 bar, mass of 20 kg, and temperature 14 degree C.[/FONT]
[FONT=comic sans ms]Thank You![/FONT]
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[P O U R I A]

Lecture 3: Thermodynamic State Space > Thermodynamic State Space

Lecture 3: Thermodynamic State Space > Thermodynamic State Space

State-Space Projections

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[/FONT]
[FONT=comic sans ms]To have some fun while learning thermodynamics.[/FONT]
[FONT=comic sans ms]I have tried to show the same state space using a software package known as Blender.[/FONT]
[FONT=comic sans ms]It's an open source software package, using which you can do very nice animations.[/FONT]
[FONT=comic sans ms]So, here we have the same system: gas in a cylinder.[/FONT]
[FONT=comic sans ms]The same state shown nicely in the three dimensional state space.[/FONT]
[FONT=comic sans ms]Where the three coordinates are pressure, temperature and mass.[/FONT]
[FONT=comic sans ms]You can see the rectangular parallelepiped and hence the values of the pressure coordinate which will be 20 bar,[/FONT]
[FONT=comic sans ms]a temperature coordinate which will be 14 degree C, and the mass coordinate which will be 20 kilogram.[/FONT]
[FONT=comic sans ms]So, this is the state space and this is our thermodynamic state of our system represented by this orange point.[/FONT]
[FONT=comic sans ms]It is not always necessary nor is it a very convenient to use a three dimensional state space.[/FONT]
[FONT=comic sans ms]Quite often it is sufficient to represent it just on two dimensions.[/FONT]
[FONT=comic sans ms]And we can have our state space and the state projected on any two dimensional projection.[/FONT]
[FONT=comic sans ms]For example, we can have the pressure temperature projection.[/FONT]
[FONT=comic sans ms]You will see the pressure temperature projection here, mass is not directly represented.[/FONT]
[FONT=comic sans ms]Alternatively, we could have the mass temperature projection.[/FONT]
[FONT=comic sans ms]Here, because the axis are mass and temperature. The pressure component is not projected.[/FONT]
[FONT=comic sans ms]The third possibility is the pressure mass projection.[/FONT]
[FONT=comic sans ms]Here you will notice that the two axes which remain are pressure and mass.[/FONT]
[FONT=comic sans ms]The temperature axis doesn't get represented.[/FONT]
[FONT=comic sans ms]I hope with this blender animation, we are sure of what we mean, and appreciate, by thermodynamic state space.[/FONT]
[FONT=comic sans ms]Thank You![/FONT]
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[P O U R I A]

Lecture 3: Thermodynamic State Space > Thermodynamic Equilibrium

Lecture 3: Thermodynamic State Space > Thermodynamic Equilibrium

Thermodynamic Equilibrium

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[FONT=comic sans ms]So, we saw that a state of a thermodynamic system can be represented by a point in the so called thermodynamic state space.[/FONT]
[FONT=comic sans ms]The question which arises is this. Is it always possible to represent a state, by state we mean[/FONT]
[FONT=comic sans ms]the thermodynamic state of a thermodynamic system, by a point in the thermodynamic state space?[/FONT]
[FONT=comic sans ms]Now remember that if you have to define a point in the geometric space all the required coordinates have to be precisely defined.[/FONT]
[FONT=comic sans ms]You can't have any confusion in any of the coordinates,[/FONT]
[FONT=comic sans ms]X has to be some precise value, Y has to be some precise value, Z has to have its precise value.[/FONT]
[FONT=comic sans ms]Suppose this is true - if the answer is yes - then we have a depiction something like this.[/FONT]
[FONT=comic sans ms]This is the state this point, and we could have the three coordinates say for example pressure, mass, temperature.[/FONT]
[FONT=comic sans ms]This is only for illustration. Depending on the system and the type of relevant properties,[/FONT]
[FONT=comic sans ms]the coordinates will change they could be two, they could be three, they could be more,[/FONT]
[FONT=comic sans ms]but sometimes it is possible that when we do the measurement we find that the pressure perhaps is not uniform.[/FONT]
[FONT=comic sans ms]If we stir the gas or instead of a gas its fluid reasonably dense and it is being stirred the pressure may not be uniform.[/FONT]
[FONT=comic sans ms]If the cylinder is exposed to the sun on one side it's possible that part of the gas is warmer than the other part.[/FONT]
[FONT=comic sans ms]In which case one more more coordinates may not be uniquely defined.[/FONT]
[FONT=comic sans ms]And if they are not uniquely defined it may not be possible for us to represent that so called state by a point.[/FONT]
[FONT=comic sans ms]We will get some sort of a nebulosity, we don't know what the state is.[/FONT]
[FONT=comic sans ms]So remember that if the answer to this question is yes, we have a state represented by a point in the thermodynamic state space.[/FONT]
[FONT=comic sans ms]And our definition is that this state is in thermodynamic equilibrium.[/FONT]
[FONT=comic sans ms]We say that the state is in thermodynamic equilibrium when all relevant properties are uniquely defined[/FONT]
[FONT=comic sans ms]and hence the state can be represented precisely by a point in the thermodynamic state space.[/FONT]
[FONT=comic sans ms]If the answer is no then here we have a crude depiction of a state not in thermodynamic equilibrium.[/FONT]
[FONT=comic sans ms]The idea of equilibrium is important in thermodynamics.[/FONT]
[FONT=comic sans ms]The idea of thermodynamic equilibrium because when we say that[/FONT]
[FONT=comic sans ms]a state is in thermodynamic equilibrium we have unique and known values of its properties[/FONT]
[FONT=comic sans ms]so we can proceed with appropriate calculations and further study of thermodynamics.[/FONT]
[FONT=comic sans ms]We can't do much when the depiction is that of non equilibrium because we don't have a point which we can precisely locate in space.[/FONT]
[FONT=comic sans ms]The idea of equilibrium is not unique to thermodynamics.[/FONT]
[FONT=comic sans ms]We have just now defined thermodynamic equilibrium, but there are other equilibria.[/FONT]
[FONT=comic sans ms]For example, we have mechanical equilibria from mechanics, from chemistry we have chemical equilibria.[/FONT]
[FONT=comic sans ms]The definitions of these equilibria are different and we pick up no fight with them.[/FONT]
[FONT=comic sans ms]Our definition of thermodynamic equilibrium is as explained that[/FONT]
[FONT=comic sans ms]a state in thermodynamic equilibrium has all its properties uniquely defined and hence is represented,[/FONT]
[FONT=comic sans ms]or representable on an appropriate thermodynamic state space by a unique point.[/FONT]
[FONT=comic sans ms]Even in thermodynamics, we will later consider when we look at zeroth law another equilibrium known as thermal equilibrium.[/FONT]
[FONT=comic sans ms]So this is just to make ourselves clear that the idea of equilibrium is not unique to thermodynamics.[/FONT]
[FONT=comic sans ms]We have defined thermodynamic equilibrium in one particular way.[/FONT]
[FONT=comic sans ms]There are other equilibria in other branches of physics even in thermodynamics,[/FONT]
[FONT=comic sans ms]we will have another idea of an equilibrium known as thermal equilibrium which we will come across when study the zeroth law of thermodynamics.[/FONT]
[FONT=comic sans ms]Thank You![/FONT]
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[P O U R I A]

Lecture 3: Thermodynamic State Space > Thermodynamic Processes

Lecture 3: Thermodynamic State Space > Thermodynamic Processes

Processes 1

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[FONT=comic sans ms]We are now going to look at thermodynamic processes or simply processes in short because everything that we do is thermodynamic.[/FONT]
[FONT=comic sans ms]In fact process is a nomenclature which is nothing but a short form, that is equivalent to a change of state.[/FONT]
[FONT=comic sans ms]and since state belongs to a system, a thermodynamic system, a process is always executed by a system.[/FONT]
[FONT=comic sans ms]So, a thermodynamic process is nothing but change in the state of a thermodynamic system[/FONT]
[FONT=comic sans ms]and hence the process is always executed by a thermodynamic system.[/FONT]
[FONT=comic sans ms]And because a change is involved the minimal thing which is required for a process is[/FONT]
[FONT=comic sans ms]you must have a system properly defined, and you must have an initial state and a final state.[/FONT]
[FONT=comic sans ms]In a visual way, let us say that we have a system and let me simplify its state space in a two dimensional way.[/FONT]
[FONT=comic sans ms]If you are comfortable you may write pressure and volume or you may write temperature and mass, whatever.[/FONT]
[FONT=comic sans ms]This is just for illustration or you could simply write X and Y, X and Y could be any two properties.[/FONT]
[FONT=comic sans ms]So, the depiction of a process is initial state, final state.[/FONT]
[FONT=comic sans ms]This is the minimal representation of a process you must have a system, you must have an initial state, and you must have a final state.[/FONT]
[FONT=comic sans ms]Now initial state and final states are big words so quite often we will use symbols like 1 and 2[/FONT]
[FONT=comic sans ms]for initial and final states or sometimes 'i' for initial 'f' for final. We will mark those things down.[/FONT]
[FONT=comic sans ms]And remember that since a change of state is involved.[/FONT]
[FONT=comic sans ms]Since, process means a change of state and since a change of state is represented by property,[/FONT]
[FONT=comic sans ms]a process involves a change in at least one property.[/FONT]
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[P O U R I A]

Lecture 3: Thermodynamic State Space > Thermodynamic Processes

Lecture 3: Thermodynamic State Space > Thermodynamic Processes

Processes 2

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[FONT=comic sans ms]A question now arises that - since a process has an initial state and a final state of a system is there a path associated with that.[/FONT]
[FONT=comic sans ms]As the system progresses from the initial state to the final state.[/FONT]
[FONT=comic sans ms]In a simplified state space you could call it simply y and x any two properties.[/FONT]
[FONT=comic sans ms]Let's say this is the initial state say i, this is the final state say f.[/FONT]
[FONT=comic sans ms]What happens to the system as the process progresses from the initial state i to the final state f?[/FONT]
[FONT=comic sans ms]There are two possibilities - one possibility is as we observe the process, it is possible[/FONT]
[FONT=comic sans ms]that the system goes through a set of quasi-static states in between.[/FONT]
[FONT=comic sans ms]It is possible that during our observation any time we find the system in some state of equilibrium as it goes from the initial state i to the final state f.[/FONT]
[FONT=comic sans ms]So, it is possible that as we observe and mark the intermediate states, we will get a set of states in equilibrium each one next to the each other.[/FONT]
[FONT=comic sans ms]And hence we will be able to draw a continuous locus from the initial state i to the final state f.[/FONT]
[FONT=comic sans ms]So, it is possible that: possibility(a) all intermediate states are states in equilibrium.[/FONT]
[FONT=comic sans ms]And hence a locus from initial state i to the final state f exists and hence we can define a path.[/FONT]
[FONT=comic sans ms]Such a process is called a quasi-static process.[/FONT]
[FONT=comic sans ms]So, this simply means that if all intermediate states are states in equilibrium and they form a locus from the initial state i to a final state f,[/FONT]
[FONT=comic sans ms]then at any stage during the process when we observed the system we will find the system[/FONT]
[FONT=comic sans ms]to be on one of these intermediate states as defined by the locus.[/FONT]
[FONT=comic sans ms]Hence a proper path is defined and in this case we call this process a quasi-static process.[/FONT]
[FONT=comic sans ms]On the other hand - it is possible that the system takes[/FONT]
[FONT=comic sans ms]such a route that it's not possible for us to have a locus from the initial state i to the final state f.[/FONT]
[FONT=comic sans ms]We know that the system was at the initial state i to begin with.[/FONT]
[FONT=comic sans ms]We know that finally at the end of the process the system happened to be in this final state f.[/FONT]
[FONT=comic sans ms]But, we don't know what happened in between; the intermediate states were not states in thermodynamic equilibrium.[/FONT]
[FONT=comic sans ms]In which case we cannot define a path. So, the other thing is a path cannot be defined.[/FONT]
[FONT=comic sans ms]Because intermediate states are not in equilibrium. Such a process is known as a non-quasi-static process.[/FONT]
[FONT=comic sans ms]Just to indicate that a process exists from initial point i to the final state f.[/FONT]
[FONT=comic sans ms]We quite often link them by means of a dotted line, and show an arrow from the initial state i to the final state f.[/FONT]
[FONT=comic sans ms]The location of the dotted line is of no consequence. It does not show the set of intermediate states.[/FONT]
[FONT=comic sans ms]It only indicates that i at the tail of the arrow is the initial state f, at the head of the arrow is the final state.[/FONT]
[FONT=comic sans ms]So, here we have an illustration on state space. So this process - let me show it by a is a quasi-static process.[/FONT]
[FONT=comic sans ms]If I have another process like this all intermediate states know b is another quasi-static process.[/FONT]
[FONT=comic sans ms]Whereas if I have a process which is non-quasi-static. Let say c, this is the depiction of a non-quasi-static process.[/FONT]
[FONT=comic sans ms]Similarly, another non-quasi-static process would be or could be denoted like this.[/FONT]
[FONT=comic sans ms]Now notice that for process a and b as the system goes from the initial state i to the final state f.[/FONT]
[FONT=comic sans ms]Take a point here at some stage during the process from i to f a system would be going through this point,[/FONT]
[FONT=comic sans ms]and that would be a state of equilibrium, that point in the thermodynamics state space.[/FONT]
[FONT=comic sans ms]And hence we can say that the process i to f a quasi-static process a is different from the process i to f the quasi-static process b.[/FONT]
[FONT=comic sans ms]Whereas the two non-quasi-static processes i to f represented by c.[/FONT]
[FONT=comic sans ms]And another i to f represented by d are simply two non-quasi-static processes.[/FONT]
[FONT=comic sans ms]The dotted line only links the initial state and the final state.[/FONT]
[FONT=comic sans ms]The locations of the dotted lines mean nothing for non-quasi-static processes, we know only the initial state and the final state.[/FONT]
[FONT=comic sans ms]So, summarising here a and b are quasi static processes and c and d are non-quasi-static processes.[/FONT]
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[P O U R I A]

Lecture 3: Thermodynamic State Space > Thermodynamic Cycles

Lecture 3: Thermodynamic State Space > Thermodynamic Cycles

Processes 3

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[FONT=comic sans ms]Let us now look at a special type of process known as a cycle.[/FONT]
[FONT=comic sans ms]Of course since we are in thermodynamics this a thermodynamic cycle.[/FONT]
[FONT=comic sans ms]We have studied processes as a change of state, so we have an initial state and a final state.[/FONT]
[FONT=comic sans ms]If it turns out that the initial state i and the final state f are the same then that process is known as a cycle.[/FONT]
[FONT=comic sans ms]Process for which the initial state and final state are the same.[/FONT]
[FONT=comic sans ms]So, the minimal representation of a cycle would be something like this - simply a dot[/FONT]
[FONT=comic sans ms]in the state space of the system involved indicating both the initial state as well as the final state.[/FONT]
[FONT=comic sans ms]However it's possible that as the process is executed the system goes away from the initial state.[/FONT]
[FONT=comic sans ms]Takes a very scenic route and comes back to the initial state and says well this is also my final state.[/FONT]
[FONT=comic sans ms]So, if it executes a cycle in quasi-static way so we will get perhaps a cycle like this.[/FONT]
[FONT=comic sans ms]This is the depiction of quasi-static cycle, so let me label it as a. So a is a quasi-static cycle.[/FONT]
[FONT=comic sans ms]I can have another quasi-static cycle. Let me call it b, b is another quasi-static cycle.[/FONT]
[FONT=comic sans ms]If you consider a throughout the process the state was known because it was a state of equilibrium,[/FONT]
[FONT=comic sans ms]but one could have - I will create another figure so as not to increase the clutter.[/FONT]
[FONT=comic sans ms]Let say this is the initial state as well as the final state.[/FONT]
[FONT=comic sans ms]And then let's say that the system takes some process, but no state during that cyclic process is a state of equilibrium.[/FONT]
[FONT=comic sans ms]So here is the depiction of a non-quasi-static cycle.[/FONT]
[FONT=comic sans ms]Notice that this visual representation of the cycle by means of a dotted line it just a representation.[/FONT]
[FONT=comic sans ms]The location of the dotted line doesn't mean anything.[/FONT]
[FONT=comic sans ms]But, whenever we have a quasi-static cycle it is represented by a proper closed loop in the thermodynamic state space.[/FONT]
[FONT=comic sans ms]Thank You![/FONT]
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[P O U R I A]

Lecture 3: Thermodynamic State Space > Processes and Properties

Lecture 3: Thermodynamic State Space > Processes and Properties

Processes and Properties

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[FONT=comic sans ms]We now consider the way property change during a process.[/FONT]
[FONT=comic sans ms]Because a process again is nothing, but a change of state and hence this implies a change in properties. At least one property.[/FONT]
[FONT=comic sans ms]Now one should realise that when a process takes place,[/FONT]
[FONT=comic sans ms]the state changes say from 1 to 2, so at least one property will change from 1 to 2.[/FONT]
[FONT=comic sans ms]It's possible that all properties will undergo a change.[/FONT]
[FONT=comic sans ms]But, remember that property depends on the state.[/FONT]
[FONT=comic sans ms]Hence, the change in property during a process depends only on the end state.[/FONT]
[FONT=comic sans ms]Let us take an illustration. Let's take Φ is a property of our system.[/FONT]
[FONT=comic sans ms]So as the process is executed from 1 to 2, the change in property will be the Φ2 - Φ1 = ΔΦ[/FONT]
[FONT=comic sans ms]final value of the property minus the initial value of the property.[/FONT]
[FONT=comic sans ms]This is the change in our property.[/FONT]
[FONT=comic sans ms]This is represented quite often by (ΔΦ) or sometimes to be specific that it process pertains to the process 1 to 2. ΔΦ one two.[/FONT]
[FONT=comic sans ms]And this change in property - one should appreciate that - depends only on the end states and not on the path.[/FONT]
[FONT=comic sans ms]Because the path may take different routes from 1 or 2,[/FONT]
[FONT=comic sans ms]but so long as the end states are the same the property phi two Φ2 of the final state[/FONT]
[FONT=comic sans ms]and the property phi one Φ1 of the initial state will not be different and hence the change in property over a process[/FONT]
[FONT=comic sans ms]from a fixed initial state to another fixed final state will be the same.[/FONT]
[FONT=comic sans ms]So, if I consider a quasi-static process from 1 to 2 like this. I will have ΔΦ 1 2 as a change in property.[/FONT]
[FONT=comic sans ms]If I take another quasi-static process from 1 to 2, it say the first process is a, second process is b.[/FONT]
[FONT=comic sans ms]Again I will have the same change in property.[/FONT]
[FONT=comic sans ms]If I consider a non-quasi-static process from 1 to 2 - let say c.[/FONT]
[FONT=comic sans ms]Again I will have the same change in property because the properties depend only on state 2 and state 1.[/FONT]
[FONT=comic sans ms]And hence the change in property will depend only on the end states and not on the path.[/FONT]
[FONT=comic sans ms]What is the implication of this for a cycle?[/FONT]
[FONT=comic sans ms]Let's consider a cycle starting from an initial state i and coming back to the same state which is also f.[/FONT]
[FONT=comic sans ms]So, this is a quasi-static cycle a and maybe I have a non-quasi-static cycle with the same initial and final state b.[/FONT]
[FONT=comic sans ms]In this case, because these are cycles, the final state is the same state as the initial state.[/FONT]
[FONT=comic sans ms]Hence, the property of the final state equals the property of the initial state Φf=Φi.[/FONT]
[FONT=comic sans ms]And hence the change in property - any property - of a system which executes a cycle is zero; ΔΦcycle=0.[/FONT]
[FONT=comic sans ms]This is something which one should remember.[/FONT]
[FONT=comic sans ms]From a mathematical point of view in thermodynamics - we say that properties depend only on the state of a system[/FONT]
[FONT=comic sans ms]from mathematics point of view any property is a point function.[/FONT]
[FONT=comic sans ms]Because a point represents a given state in thermodynamic state space.[/FONT]
[FONT=comic sans ms]Also since Φ12=Φ2-Φ1 change in property final value minus initial value does not depend on the path.[/FONT]
[FONT=comic sans ms]So, if you consider a small part of the process with a change in property dΦ integrate it from 1 to 2.[/FONT]
[FONT=comic sans ms]This integral becomes delta phi one two and this is independent of the path.[/FONT]
[FONT=comic sans ms]And hence in mathematical terms "dΦ" is an exact differential.[/FONT]
[FONT=comic sans ms]A mathematical property of any exact differential is that when you integrate it over from a given point to another point[/FONT]
[FONT=comic sans ms]the value of the integral does not depend on path.[/FONT]
[FONT=comic sans ms]In fact this characteristic that the differential of a property is an exact differential will be used in reverse[/FONT]
[FONT=comic sans ms]to define two of the most important properties that we come across in thermodynamics, energy and entropy.[/FONT]
[FONT=comic sans ms]Thank You![/FONT]
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[P O U R I A]

Lecture 4: The Work Interaction > Thermodynamic Interactions

Lecture 4: The Work Interaction > Thermodynamic Interactions

Thermodynamic Interactions

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[FONT=comic sans ms]Let us now look at thermodynamic interactions.[/FONT]
[FONT=comic sans ms]The scheme of thermodynamics is to consider the behaviour of two systems.[/FONT]
[FONT=comic sans ms]Let us call it system A. Let's call this system, system B.[/FONT]
[FONT=comic sans ms]We may call this system A as system, system B as surroundings.[/FONT]
[FONT=comic sans ms]But lets continue with this nomenclature system A and system B.[/FONT]
[FONT=comic sans ms]What this two systems do is they - transfer energy.[/FONT]
[FONT=comic sans ms]They have a transaction of energy transfer between them.[/FONT]
[FONT=comic sans ms]And because of this energy transfer - system A undergoes a change of state for a process from an initial state say A1 to a final state say A2.[/FONT]
[FONT=comic sans ms]And system B also undergoes a process, and its state changes from an initial state B1 to its final state B2.[/FONT]
[FONT=comic sans ms]These energy transfers require that two systems are involved.[/FONT]
[FONT=comic sans ms]And second one the energy we have not exactly defined - what is meant by energy,[/FONT]
[FONT=comic sans ms]but, let's use our feeling from our study of physics - is transported from one system to the other across the boundary that separates them.[/FONT]
[FONT=comic sans ms]So, we can consider a boundary separating the two and what transaction takes place must be across this boundary.[/FONT]
[FONT=comic sans ms]These energy transfers are known as interactions.[/FONT]
[FONT=comic sans ms]And the whole scheme of thermodynamics is to study the interactions.[/FONT]
[FONT=comic sans ms]Type of interaction, the quantification of interactions,[/FONT]
[FONT=comic sans ms]and relate them to change in the state of system A and the change in the state of system B.[/FONT]
[FONT=comic sans ms]In this course, we are going to look at two types of interactions.[/FONT]
[FONT=comic sans ms]And thermodynamics allows only two types of thermodynamic interactions.[/FONT]
[FONT=comic sans ms]The first one is the work type of interaction.[/FONT]
[FONT=comic sans ms]And this interaction we will define, but this interaction is a primitive.[/FONT]
[FONT=comic sans ms]In the sense that it is defined in other branches of physics.[/FONT]
[FONT=comic sans ms]Right from our high school days we know - what is work,[/FONT]
[FONT=comic sans ms]and how work is defined, and how work is measured.[/FONT]
[FONT=comic sans ms]But, thermodynamics defines another type of interaction which is the heat type of interaction.[/FONT]
[FONT=comic sans ms]And this is defined by thermodynamics.[/FONT]
[FONT=comic sans ms]Our next major topic would be a study of the work interaction.[/FONT]
[FONT=comic sans ms]Thank you.[/FONT]
[FONT=comic sans ms]

​

 

[P O U R I A]

Lecture 4: The Work Interaction > The Work Interaction

Lecture 4: The Work Interaction > The Work Interaction

The Work Interaction 1

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[FONT=comic sans ms]Welcome. We now look at the first of the two interactions that we are going to study.[/FONT]
[FONT=comic sans ms]The work interaction, the idea of work is a primitive in thermodynamics, it is defined in other branches of physics.[/FONT]
[FONT=comic sans ms]For example, it is defined in mechanics and electricity, magnetism, fluid mechanics and so on.[/FONT]
[FONT=comic sans ms]The basic idea of work if you look at the mechanical definition is we have a force and we have a displacement.[/FONT]
[FONT=comic sans ms]If the point of application of the force moves in the direction of the displacement then we have work being done.[/FONT]
[FONT=comic sans ms]Since, we have force as a vector, displacement is also a vector, we have to have a dot product here,[/FONT]
[FONT=comic sans ms]so that the component of displacement in the direction of force or the component of force in the direction of displacement is taken into account.[/FONT]
[FONT=comic sans ms]The other branches of physics also define it in somewhat similar way except that we can have a sort of a generalised force and the generalised displacement.[/FONT]
[FONT=comic sans ms]Let us consider some examples and we will now look at it from thermodynamic point of view.[/FONT]
[FONT=comic sans ms]So we will have a system and we will have another system or surroundings and for us work interaction has to be energy in transit.[/FONT]
[FONT=comic sans ms]So, there has to be a proper interaction between the system and the surroundings.[/FONT]
[FONT=comic sans ms]Let us take one illustration, let us say that we have a rod or if you wish you could even consider it to be spring[/FONT]
[FONT=comic sans ms]and let us say that there is a loop at the end of it, we have a somebody or something which is pulling it.[/FONT]
[FONT=comic sans ms]Let us say that this rod is our system and it is pulled by someone, say my hand, and because of it being pulled[/FONT]
[FONT=comic sans ms]there is a tension in the rod, the rod pulls me back and let the tension be T, tension is a force and because of my pull,[/FONT]
[FONT=comic sans ms]let us say that the initial length of the rod is L and it gets extended by a small amount dL.[/FONT]
[FONT=comic sans ms]So I am holding something in my hand like a rod and I am pulling it and because I pull it gets extended a bit.[/FONT]
[FONT=comic sans ms]Of course the pencil is too stiff to get extended, but I could use a spring and extend it a bit.[/FONT]
[FONT=comic sans ms]Now in this particular case the system is the rod or the spring and the small amount of work done is -T dL.[/FONT]
[FONT=comic sans ms]Where T is the tension, so we have something like a force here and we have the displacement dL.[/FONT]
[FONT=comic sans ms]We will see and discuss this negative sign later.[/FONT]
[FONT=comic sans ms]Let us take another example, all of us have a mobile phone and each mobile phone has a battery in it or a chargeable cell.[/FONT]
[FONT=comic sans ms]So let us say that we have such a chargeable cell here, let us say that it has a positive terminal and it has a negative terminal, let us say that the cell is our system.[/FONT]
[FONT=comic sans ms]Let's have a connection from the positive terminal and the negative terminal and let the electric potential be E of the positive terminal with respect to negative terminal,[/FONT]
[FONT=comic sans ms]this could be 1.5 volts, 2 volts, 3 volts depending on the type of cell that we have.[/FONT]
[FONT=comic sans ms]And let us say that these terminals are connected to some load, it could be the circuit of the mobile phone,[/FONT]
[FONT=comic sans ms]it could be a simple resistor, a small lamp and let us say that this circuit consumes a charge dq.[/FONT]
[FONT=comic sans ms]Now charge is conserve so whatever is the charge taken from the positive terminal has to be returned to the negative terminal.[/FONT]
[FONT=comic sans ms]In terms of i, the current, if the current is i this will be the current into the small amount of time dt during[/FONT]
[FONT=comic sans ms]which the current flows and we know that in this case we will say that the work done by our system will be +E dq or if you want to write it as +Eidt.[/FONT]
[FONT=comic sans ms]Notice the plus sign here.[/FONT]
[FONT=comic sans ms]Another illustration which we will look at is some reasonably thick liquid so the system is some liquid.[/FONT]
[FONT=comic sans ms]And what we have is a stirrer dipped inside it, and what we do is we try to rotate the stirrer by a small angle d-theta.[/FONT]
[FONT=comic sans ms]The liquid is thick, it is viscous, it could be very viscous like condensed milk, you know how difficult it is to stir condensed milk.[/FONT]
[FONT=comic sans ms]But, if you try to stir it, the liquid imposes a torque opposing the stirrer which we have to overcome, let the torque be tau.[/FONT]
[FONT=comic sans ms]In this case the system is the liquid and we now say that the work done is -tau d-theta.[/FONT]
[FONT=comic sans ms]Again notice that there is a negative sign here.[/FONT]
[FONT=comic sans ms]Let us take one more example, let us consider a typical cylinder piston arrangement and let us say that the piston for simplicity a leak proof frictionless piston encloses[/FONT]
[FONT=comic sans ms]some fluid say a gas inside it, so the system is the gas in this cylinder piston arrangement.[/FONT]
[FONT=comic sans ms]Let us say that the pressure of the gas is p and this acts uniformly on the piston.[/FONT]
[FONT=comic sans ms]Let the area of the piston be A, area of the piston exposed to the fluid and because of this the force[/FONT]
[FONT=comic sans ms]which is acting on the piston - presence of the fluid is p*A and let us say that the piston is initially held in place because of an equal and opposite[/FONT]
[FONT=comic sans ms]force being applied from the outside maybe I'm holding it so that it doesn't fly off and if I relax myself a bit[/FONT]
[FONT=comic sans ms]the piston will move by a distance dx, that is the displacement of the piston.[/FONT]
[FONT=comic sans ms]And now we will say that for our system which is the gas in this cylinder piston arrangement, the work done will be the force into the displacement.[/FONT]
[FONT=comic sans ms]The force is p*A*dx and since area and displacement when multiplied give you the change in the volume of the system this becomes pdV.[/FONT]
[FONT=comic sans ms]So in this particular case the work done by the gaseous system is pdv and in particular we can write it as +pdV if we are conscious of the sign.[/FONT]
[FONT=comic sans ms]

​

 

[P O U R I A]

Lecture 4: The Work Interaction > The Work Interaction

Lecture 4: The Work Interaction > The Work Interaction

The Work Interaction 2

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[FONT=comic sans ms]So we have looked at a few typical elementary work interactions, small work interactions, dW.[/FONT]
[FONT=comic sans ms]A few things to note - first in every case we have a system and we have a surroundings.[/FONT]
[FONT=comic sans ms]The gas was the system, the piston was the surrounding.[/FONT]
[FONT=comic sans ms]Liquid was the system, the stirrer was the surrounding.[/FONT]
[FONT=comic sans ms]The electric cell was the system, the circuit of the cell phone was the surrounding.[/FONT]
[FONT=comic sans ms]Second thing is to note that - the final format of the work interaction turned out to be some plus or minus sign.[/FONT]
[FONT=comic sans ms]Some X*dY. This was the final format.[/FONT]
[FONT=comic sans ms]pdV, Edq, tau d-theta, TdL, everything was in the XdY format.[/FONT]
[FONT=comic sans ms]Third, some sign convention was involved.[/FONT]
[FONT=comic sans ms]In some cases we had a + sign here, in a few cases we had a - sign here.[/FONT]
[FONT=comic sans ms]Then we should also know and note that often, but not always X here is an intensive property of our system.[/FONT]
[FONT=comic sans ms]Whereas the second component dY in which Y is involved, Y is an extensive property.[/FONT]
[FONT=comic sans ms]So, the work done is quite often, but not always is represented by some intensive property multiplied by a change or a differential of an appropriate extensive property.[/FONT]
[FONT=comic sans ms]This happens often but not always.[/FONT]
[FONT=comic sans ms]And the fifth point to note is that some types - what we called modes - of work interaction are one-way.[/FONT]
[FONT=comic sans ms]We will look at the illustrations again to understand what we mean by this? Some other modes are two-way.[/FONT]
[FONT=comic sans ms]Let us go back to our illustrations and look at these points again.[/FONT]
[FONT=comic sans ms]Let's look at this situation where our system was the gas in the cylinder piston arrangement.[/FONT]
[FONT=comic sans ms]You will notice that the final format which is pdV, p happens to be an intensive property, whereas volume happens to be an extensive property.[/FONT]
[FONT=comic sans ms]So here, the intensive, extensive product exists. The sign here is plus.[/FONT]
[FONT=comic sans ms]System is gas, surrounding is the piston.[/FONT]
[FONT=comic sans ms]And here you will notice that initially when the piston is at rest with the force of the gas on the piston, and the externally applied force imbalance, no work is done.[/FONT]
[FONT=comic sans ms]If the external forces relaxes a bit, the piston will expand, and the system will do work on the surrounding.[/FONT]
[FONT=comic sans ms]The pdV product because dV will be a positive number, volume will increase, dW will be positive.[/FONT]
[FONT=comic sans ms]The system will do work on the surroundings.[/FONT]
[FONT=comic sans ms]Whereas, if the external force slightly increases then the piston will move in compressing the gas.[/FONT]
[FONT=comic sans ms]dx will be negative, volume will reduce, dV will be negative, and dW will be a numerically negative quantity.[/FONT]
[FONT=comic sans ms]So, this is an example of a two way work interaction.[/FONT]
[FONT=comic sans ms]It's possible for the system to expand and do work on the piston.[/FONT]
[FONT=comic sans ms]It is possible for the piston to move into the system compressing the system, and hence the work done by the system will be negative.[/FONT]
[FONT=comic sans ms]Let us come to the illustration of the liquid being stirred.[/FONT]
[FONT=comic sans ms]Here you will notice that neither tau nor d-theta are properties of the system.[/FONT]
[FONT=comic sans ms]Properties of the system are not the torque.[/FONT]
[FONT=comic sans ms]The torque doesn't exist unless we try to stir it.[/FONT]
[FONT=comic sans ms]We just keep a liquid in a vessel, there is no torque involved even if you just insert a stirrer and leave it there.[/FONT]
[FONT=comic sans ms]So, here tau and d-theta are not properties of the system.[/FONT]
[FONT=comic sans ms]So, this is not included in what happens often.[/FONT]
[FONT=comic sans ms]And now you will notice that if I insert a stirrer and try to rotate it, I have to overcome a torque,[/FONT]
[FONT=comic sans ms]and hence my work done by the system is negative, -tau d-theta.[/FONT]
[FONT=comic sans ms]But, if I just keep the stirrer there and asked the liquid "hey Mr liquid, stir the stirrer".[/FONT]
[FONT=comic sans ms]It won't do. So the negative of this doesn't exist.[/FONT]
[FONT=comic sans ms]So this is an illustration of a one way work mode.[/FONT]
[FONT=comic sans ms]Come to the previous illustration that of an electric cell.[/FONT]
[FONT=comic sans ms]You buy a cell or you create a cell - it has a typical potential associated with it.[/FONT]
[FONT=comic sans ms]A typical dry cell will have an potential of 1.5 Volts.[/FONT]
[FONT=comic sans ms]May be different designs will have different.[/FONT]
[FONT=comic sans ms]Leclanche cell may be 1.2 volts.[/FONT]
[FONT=comic sans ms]You can create various types of cells in your physical chemistry lab, electrochemical experiments.[/FONT]
[FONT=comic sans ms]Now, many cells particularly those in our laptops, mobiles, tablets, some torches are rechargeable.[/FONT]
[FONT=comic sans ms]In a sense that they can discharge and work on a load.[/FONT]
[FONT=comic sans ms]For example, it can drive our laptop or work our mobile,[/FONT]
[FONT=comic sans ms]in which case the work done by our cell, the system will be positive.[/FONT]
[FONT=comic sans ms]Cell will be doing work on its surroundings which is say the mobile phone.[/FONT]
[FONT=comic sans ms]Whereas I can connect this to a charger to charge it.[/FONT]
[FONT=comic sans ms]In which case current will be in the opposite direction, but the direction of the potential will remain the same.[/FONT]
[FONT=comic sans ms]So dq will be negative. E will be positive.[/FONT]
[FONT=comic sans ms]So work done by the system will be negative.[/FONT]
[FONT=comic sans ms]So if it is a rechargeable cell, charging and discharging is a two way work mode.[/FONT]
[FONT=comic sans ms]Whereas, if it is a non-rechargeable cell - a typical dry cell which you can buy.[/FONT]
[FONT=comic sans ms]Well, we can not charge it or we can not charge it so easily.[/FONT]
[FONT=comic sans ms]So that is the typical situation of a one way work mode.[/FONT]
[FONT=comic sans ms]I leave it to you as an exercise to discuss - whether this spring being extended is a one way work mode or a two way work mode.[/FONT]
[FONT=comic sans ms]Thank You.[/FONT]
[FONT=comic sans ms]

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[P O U R I A]

Lecture 5: Thermodynamic Definition of Work > Thermodynamic Definition of Work

Lecture 5: Thermodynamic Definition of Work > Thermodynamic Definition of Work

Operational Definitions

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[FONT=comic sans ms]After having looked at some simple work interactions, it's time for us to look at a thermodynamic definition of work.[/FONT]
[FONT=comic sans ms]Before we do that it is necessary for us to study - what we mean by operational definitions.[/FONT]
[FONT=comic sans ms]It is necessary to look at these because our thermodynamic definition of work will be a proper operational definition.[/FONT]
[FONT=comic sans ms]The idea of operational definition was first proposed by Prof P W Bridgman.[/FONT]
[FONT=comic sans ms]A well known physicist, Nobel laureate, and a person who worked significantly in thermodynamics and in the physics of high pressure.[/FONT]
[FONT=comic sans ms]His books the nature of physical theory and the nature of thermodynamics are classics.[/FONT]
[FONT=comic sans ms]And those who are interested in the history of physics and the development of the formulation of physics should look up these books in an appropriate library.[/FONT]
[FONT=comic sans ms]Bridgman's idea of operational definition which we will adopt is like this.[/FONT]
[FONT=comic sans ms]An operational definition allows us to decide whether some item X is applicable by using a procedure and a procedure is defined as a series of operations which one can execute.[/FONT]
[FONT=comic sans ms]And these operations will finally tell us whether X is applicable, or not - end up with yes, no.[/FONT]
[FONT=comic sans ms]Let us consider the operational definition of a system.[/FONT]
[FONT=comic sans ms]Now suppose we are given X something is X a system from the point of view of thermodynamics.[/FONT]
[FONT=comic sans ms]What would be the operational definition? We will ask ourselves.[/FONT]
[FONT=comic sans ms]Question one, does it define a region in space?[/FONT]
[FONT=comic sans ms]Question two, are all its boundaries properly defined?[/FONT]
[FONT=comic sans ms]Question three, hence does it have a definite volume at any instant in time?[/FONT]
[FONT=comic sans ms]Well if the answer to all these questions is yes yes yes then yes, X is a system.[/FONT]
[FONT=comic sans ms]This would be the operational definition of a system.[/FONT]
[FONT=comic sans ms]Similarly one can have a operational definitions of a process, operational definition of a state,[/FONT]
[FONT=comic sans ms]operational definition of many other things which we come across in physics.[/FONT]
[FONT=comic sans ms]Thank You.[/FONT]
[FONT=comic sans ms]

​

 

[P O U R I A]

Lecture 5: Thermodynamic Definition of Work > Thermodynamic Definition of Work

Lecture 5: Thermodynamic Definition of Work > Thermodynamic Definition of Work

Thermodynamic Definition of Work 1

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[/FONT]
[FONT=comic sans ms]Let's look at the thermodynamic definition of work.[/FONT]
[FONT=comic sans ms]This is required because various branches of physics define the work interaction in different ways.[/FONT]
[FONT=comic sans ms]And we have to have a proper definition, so that we accept some interaction as a work interaction.[/FONT]
[FONT=comic sans ms]The requirement for work to be considered as work interaction in thermodynamics are as follows.[/FONT]
[FONT=comic sans ms]First one, the interaction must be an energy interaction, and it should be between two systems.[/FONT]
[FONT=comic sans ms]So, two systems must be involved, System A system B, or a system and its surroundings.[/FONT]
[FONT=comic sans ms]Second one is that - this interaction must be completely reducible to the raise of a weight, by weight we mean some mass m in a gravitational field g.[/FONT]
[FONT=comic sans ms]This must be raised against the force of gravity.[/FONT]
[FONT=comic sans ms]So, the raise of a weight that is mass in a gravitational field is considered the basic idea of work,[/FONT]
[FONT=comic sans ms]and hence we consider that to be a work interaction provided that interaction is completely reducible to the raise of a weight.[/FONT]
[FONT=comic sans ms]And for this complete reduction there is a qualification this should be by primitive means, that means, means which are defined in other branches of physics.[/FONT]
[FONT=comic sans ms]For example, we can use chains and pulleys.[/FONT]
[FONT=comic sans ms]We can use pistons and cylinders.[/FONT]
[FONT=comic sans ms]We can use gears.[/FONT]
[FONT=comic sans ms]We can use block and tackle.[/FONT]
[FONT=comic sans ms]We can use anything which is properly defined.[/FONT]
[FONT=comic sans ms]Important thing to note is idealisations are acceptable.[/FONT]
[FONT=comic sans ms]In the sense we can consider mass-less, inertia-less, friction-less pulleys.[/FONT]
[FONT=comic sans ms]We can consider hundred percent efficient electrical generators and electrical motors.[/FONT]
[FONT=comic sans ms]we can consider friction-less movement.[/FONT]
[FONT=comic sans ms]We can consider inflexible mass-less strings all idealisation is possible.[/FONT]
[FONT=comic sans ms]However black box approach - saying, well, I have something which we will do it for me - that's not acceptable.[/FONT]
[FONT=comic sans ms]Thank You.[/FONT]

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[P O U R I A]

Lecture 5: Thermodynamic Definition of Work > Thermodynamic Definition of Work

Lecture 5: Thermodynamic Definition of Work > Thermodynamic Definition of Work

Thermodynamic Definition of Work 2​

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[/FONT]
[FONT=comic sans ms]Welcome back.[/FONT]
[FONT=comic sans ms]We now look at the operational definition of the work interaction.[/FONT]
[FONT=comic sans ms]This is the proper thermodynamic definition of work.[/FONT]
[FONT=comic sans ms]We ask ourselve this question, since thermodynamics requires that work as an interaction must take place between two systems.[/FONT]
[FONT=comic sans ms]Let's consider two systems, a system A and a system B.[/FONT]
[FONT=comic sans ms]I am showing them apart just for clarity.[/FONT]
[FONT=comic sans ms]Let this be the boundary between them and let there be some interaction I between the systems A and B.[/FONT]
[FONT=comic sans ms]This is let's say the way we have shown the direction the interaction from system A to system B.[/FONT]
[FONT=comic sans ms]Because of this interaction the state of system A will change, and let the initial state of A be A1, and let its final state be A2.[/FONT]
[FONT=comic sans ms]Because of this interaction the state of system B will also change.[/FONT]
[FONT=comic sans ms]Let B1 be its initial state and B2 to be its final state.[/FONT]
[FONT=comic sans ms]A question which we now ask ourselves, is the interaction I the work type of interaction from the thermodynamics point of view.[/FONT]
[FONT=comic sans ms]So, here we want an answer yes or no.[/FONT]
[FONT=comic sans ms]Particularly, we look at cases where the answer is a resounding yes.[/FONT]
[FONT=comic sans ms]Because, if work interaction is mixed up with some other type of interaction then the answer would definitely be no and if the answer is yes, if I is purely a work interaction.[/FONT]
[FONT=comic sans ms]What is its direction and what is its magnitude?[/FONT]
[FONT=comic sans ms]The operational definition follows a few steps, notice that the requirement is that - the interaction should lead to nothing but the raise of a weight.[/FONT]
[FONT=comic sans ms]So, in the first step what we try to do is the following - we have our system A, we let it undergo the same interaction.[/FONT]
[FONT=comic sans ms]Let it behave as if it is interacting with system B and the interaction is I as required.[/FONT]
[FONT=comic sans ms]So nothing changes from the point of view of system A.[/FONT]
[FONT=comic sans ms]However, we try to replace system B by another system,[/FONT]
[FONT=comic sans ms]you may call it even contraption, but nevertheless it's a thermodynamic system C1.[/FONT]
[FONT=comic sans ms]We try to discover, invent, such a system whose final result would be nothing, but raise of a weight - that means let it raise a mass m1 in a gravitational field g, up by a height say h1.[/FONT]
[FONT=comic sans ms]The requirement on C1 is that it must be a primitive system defined using principles in other branches of physics.[/FONT]
[FONT=comic sans ms]It must be fully defined, no black boxes will work and there should be no change in the state of C1.[/FONT]
[FONT=comic sans ms]This is also very important.[/FONT]
[FONT=comic sans ms]That means C1 can undergo a cycle - can execute a cycle, or it need not execute any process, it executes no process.[/FONT]
[FONT=comic sans ms]Actually no process is an extreme example of a cycle.[/FONT]
[FONT=comic sans ms]The initial condition and a final condition are unchanged, same.[/FONT]
[FONT=comic sans ms]And there is no process involved at all the system does not even move from its initial state.[/FONT]
[FONT=comic sans ms]Notice, that the required thing is the raise of a weight, a lowering will not do, it has to go up like this, ok.[/FONT]
[FONT=comic sans ms]Now, it's possible that we are able to setup C1, so we come to now the first conclusion.[/FONT]
[FONT=comic sans ms]If C1 can be setup as required, then we make the following conclusions.[/FONT]
[FONT=comic sans ms]First conclusion is I is work and nothing else, it's purely work.[/FONT]
[FONT=comic sans ms]b the quantitative we say work done by system A is plus m1 g h1, this will be positive number.[/FONT]
[FONT=comic sans ms]Work done by system B will be minus m1 g h1, this will be a negative quantity.[/FONT]
[FONT=comic sans ms]And third thing we say is system A does work on system B.[/FONT]
[FONT=comic sans ms]But, it is possible that we are not able to setup this required system C1, and the conclusion is possible only if we can setup C1.[/FONT]
[FONT=comic sans ms]So it is possible that C1 can not be setup.[/FONT]
[FONT=comic sans ms]So, the next step is if C1 can not be setup as specified then we go to step two.[/FONT]
[FONT=comic sans ms]Now, here what we do is the following.[/FONT]
[FONT=comic sans ms]We leave system B undisturbed, it behaves as if A is interacting with it and the interaction is I as before it undergoes the change of state from B1 to B2, so nothing changes from its point of view.[/FONT]
[FONT=comic sans ms]However, now we replace A by a system which would do the following - let us call this system C2 and we check whether such a system can be set up.[/FONT]
[FONT=comic sans ms]First, C2, as required for C1, should be made up of primitive mechanisms, and it should undergo no net change in state - the same conditions which were put on C1.[/FONT]
[FONT=comic sans ms]The net effect of replacing A by C2 is that some mass say m2 in a gravitational field g should be raised, mind you raised not lowered, by a height h2.[/FONT]
[FONT=comic sans ms]Again, let me emphasise that raise is important, and now we conclude that if C2 can be setup then a the interaction I is work,[/FONT]
[FONT=comic sans ms]b work done by system B is plus m2 g h2, which will be a positive number and work done by system A is minus m2 g h2, which is a negative number.[/FONT]
[FONT=comic sans ms]And we say finally system B does work on system A.[/FONT]
[FONT=comic sans ms]The conclusions are similar to the conclusions of step one, but the other way A and B get interchanged and of course 1 and 2 get interchanged.[/FONT]
[FONT=comic sans ms]It is also possible that we can not setup C1 nor can we setup C2.[/FONT]
[FONT=comic sans ms]As required, then, the conclusion is - the interaction I is not completely a work interaction.[/FONT]
[FONT=comic sans ms]It may be work in part, but definitely there is a component which is the non work type of interaction.[/FONT]
[FONT=comic sans ms]Later on we will define this non work type of interaction as the heat interaction.[/FONT]
[FONT=comic sans ms]Thank You.[/FONT][/LEFT]

 

[P O U R I A]

Lecture 5: Thermodynamic Definition of Work > Thermodynamic Definition of Work

Lecture 5: Thermodynamic Definition of Work > Thermodynamic Definition of Work

Sign Convention for Work

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[FONT=comic sans ms]We notice that while preparing or setting up the operational definition of work, we have used a sign convention.[/FONT]
[FONT=comic sans ms]Work is an interaction, so there is a direction involve.[/FONT]
[FONT=comic sans ms]Either system A does work on system B or system B does work on system A.[/FONT]
[FONT=comic sans ms]So we have to decide which direction is positive.[/FONT]
[FONT=comic sans ms]Usually, we have a habit of saying left to right is a positive direction.[/FONT]
[FONT=comic sans ms]Bottom to top is the positive direction.[/FONT]
[FONT=comic sans ms]But that's by convention nothing prevents us from using downward as a positive direction or the leftward as the positive direction.[/FONT]
[FONT=comic sans ms]So, in this case our sign convention is that - work done by a system which leads to the raise of weight is positive.[/FONT]
[FONT=comic sans ms]And work done on a system mind you that this is our convention and this is the convention which is often used by mechanical engineers and physicists.[/FONT]
[FONT=comic sans ms]This is not the only possible convention and an exactly opposite scheme is quite often used by chemists and chemical engineers.[/FONT]
[FONT=comic sans ms]However, because we are in the physics and mechanical engineering domain our background is mechanical engineering,[/FONT]
[FONT=comic sans ms]we will be using this sign convention.[/FONT]
[FONT=comic sans ms]Thank You.[/FONT]
[FONT=comic sans ms]

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[P O U R I A]

Lecture 6: Evaluation of Work > Evaluation of Work

Lecture 6: Evaluation of Work > Evaluation of Work

Evaluation of Work

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[FONT=comic sans ms]Welcome back.[/FONT]
[FONT=comic sans ms]We are now going to look at how the work interaction is evaluated.[/FONT]
[FONT=comic sans ms]We have seen that any system may have different modes of work.[/FONT]
[FONT=comic sans ms]Let us say that we have a gas in a cylinder piston arrangement then it is possible that it will be able to expand, and we will have an expansion mode.[/FONT]
[FONT=comic sans ms]We may even insert a stirrer and we will have a stirrer mode, we may have other modes.[/FONT]
[FONT=comic sans ms]For example, it could be a dielectric, we could charge and discharge it electrically, so we could have an electrical mode of work.[/FONT]
[FONT=comic sans ms]So in such cases we can say that the total work interaction will be a sum of the work interactions in various modes, expansion mode, stirrer mode, the electrical mode, plus others.[/FONT]
[FONT=comic sans ms]Thermodynamics does not restrict the number of modes of work that a system may have.[/FONT]
[FONT=comic sans ms]Now since we have seen the elementary work interactions and we can sum them up.[/FONT]
[FONT=comic sans ms]We have seen the various components, so in principle we can say that to go from this equation to this equation,[/FONT]
[FONT=comic sans ms]the integrated form, we may just integrate this, and the integration would give us from the initial state to the final state integral one to two plus integration of the[/FONT]
[FONT=comic sans ms]stirrer work interaction plus integration of the electrical work interaction plus others.[/FONT]
[FONT=comic sans ms]And since we know for example that the expansion work element dW expansion is pdV.[/FONT]
[FONT=comic sans ms]We can write the first integral as integral p dV from the initial state one to the final state two over the process.[/FONT]
[FONT=comic sans ms]Similarly, the second one would be minus tau d theta over the process from one to two.[/FONT]
[FONT=comic sans ms]The third one could be E dq over the process and so on.[/FONT]
[FONT=comic sans ms]Now the question that arises is there is a process of integration here. Is it always possible for this, we will have to look at the details of the process.[/FONT]
[FONT=comic sans ms]Let us consider the first of the integrals which leads to the expansion work, integral p dV.[/FONT]
[FONT=comic sans ms]Now we know integration is a area under a curve, so let's look at the detail of the process.[/FONT]
[FONT=comic sans ms]It is possible that the process from some initial state one to some final state two is some quasi-static-process, with a continuous locus from the initial state one to the final state two.[/FONT]
[FONT=comic sans ms]In this case the integral can be evaluated by some means and will represent the area under this curve.[/FONT]
[FONT=comic sans ms]This a quasi-static process and integral p dV can be evaluated.[/FONT]
[FONT=comic sans ms]But, on the other hand the system may execute a process from the initial state one to the final state two by some non-quasi-static means.[/FONT]
[FONT=comic sans ms]In which case since the intermediate states are not known to us, the area under the curve remains unevaluatable.[/FONT]
[FONT=comic sans ms]So, this is a non-quasi-static process and hence integral pdV cannot be evaluated.[/FONT]
[FONT=comic sans ms]This does not mean that expansion work doesn't exist.[/FONT]
[FONT=comic sans ms]The system may do some expansion work, however we cannot evaluate that expansion work as an integral.[/FONT]
[FONT=comic sans ms]So, what we remember from here is that if the process is quasi-static then the related work interaction can be evaluated as an integral,[/FONT]
[FONT=comic sans ms]if the process is non-quasi-static then we cannot evaluate the work interaction as an integral.[/FONT]
[FONT=comic sans ms]One more important thing which we should remember while evaluating work is the following - let us say that our system executes some expansion work in a quasi- static process.[/FONT]
[FONT=comic sans ms]So, let us say this is the initial state one, this is the final state two.[/FONT]
[FONT=comic sans ms]Let us say that in one case the system executes a process from the initial state one to two.[/FONT]
[FONT=comic sans ms]A quasi-static process which can be depicted like this, let me say this is one-a-two.[/FONT]
[FONT=comic sans ms]In this case it is very clear that the area under this curve shown by hashed black lines represents W expansion in the process one-a-two.[/FONT]
[FONT=comic sans ms]But, it's possible that in some other instance the same system executes another quasi-static process from one to two but this time the process looks like this represent[/FONT]
[FONT=comic sans ms]it as one-b-two and now we realise that the value of the integral will be different, now it is shown by hashed red lines.[/FONT]
[FONT=comic sans ms]So, we can say that this represents W expansion by the system one-b-two.[/FONT]
[FONT=comic sans ms]So what do we learn from here?[/FONT]
[FONT=comic sans ms]We learn from here is the following - One: W expansion and for that matter any component of W.[/FONT]
[FONT=comic sans ms]We have just taken an illustration of the expansion here depends on the path.[/FONT]
[FONT=comic sans ms]And hence we can say that the work interaction for a process depends on the path not just on the initial and final states.[/FONT]
[FONT=comic sans ms]And because of this, we say - here we go into calculus - that hence, integral dW from one to two is path dependent and hence, in a mathematical sense dW is not an exact differential.[/FONT]
[FONT=comic sans ms]In calculus an exact differential is differential of something like dx or dy, when integrated is independent of the path.[/FONT]
[FONT=comic sans ms]If it is dependent on the path, it is not an exact differential.[/FONT]
[FONT=comic sans ms]And because of this, you will find in some textbooks dW indicate that it is not an exact differential, it is represented as d cross W or d prime W,[/FONT]
[FONT=comic sans ms]It is not always necessary to do this, all that we have to do as good students of thermodynamics is to remember[/FONT]
[FONT=comic sans ms]that dW is not an exact differential, and hence when you integrate it the value of that integral,[/FONT]
[FONT=comic sans ms]if you are able to evaluate it for a quasi-static process will depend on the path.[/FONT]
[FONT=comic sans ms]Thank You.[/FONT]
[FONT=comic sans ms]

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