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hello dear students
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welcome to the course of engineering
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thermodynamics myself
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from mechanical department of lga
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institute of engineering and technology
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so today we are going to discuss about
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introduction and basic concept
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of engineering thermodynamics now the
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points that we are going to follow today
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is the very first is microscopic and
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microscopic point of view that will be
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followed by
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thermodynamic system and control volume
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that will be followed by concept of
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continuum
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and at last we will discuss certain
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definitions
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like properties state change of state
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then path process as well as cycle now
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let us discuss about first point that is
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microscopic and microscopic point of
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view
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so microscopic point of view is also
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known as
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statistical approach why it is known as
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statistical approach
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let us understand before that
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microscopic approach means what
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so microscopic means the events
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occurring at molecular level
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are taken into account that will be
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known as microscopic approach
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meaning you will be bothered about
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individual behavior
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of molecule right so you will track down
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individual molecule
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so that will be known as microscopic
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approach now
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why it is called a statistical approach
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let us understand that
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so as you can see on the screen i have
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taken certain molecules
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in the vessel now let us assume that
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there are 10 is to power 20 molecules
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present in over here
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now if i want to define the coordinates
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for position
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of any one molecule then what i will
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have to do is i will require three
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coordinates that is
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x y and z now if i want to define
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velocity of that particular molecule
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then i will require
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three velocity components respectively
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in x
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y and z direction so together
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if i want to define velocity of all
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molecules present
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in this vessel then what will i have to
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do is i will require
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6 into 10 to power 20 equations
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and if it is difficult to solve this
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many equations together
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and simultaneously so what one can do is
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one can do the statistical mean
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of this equations right so that is why
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this
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approach is also known as statistical
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approach
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now the very next approach is
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microscopic approach
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it is also known as classical approach
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why it is known as microscopic approach
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so simple events occurring at molecular
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level
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are taken into account that means what
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that means
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simple you will take average behavior of
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all molecules
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right so let us understand it by simple
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example for example
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a room temperature is defined to be 25
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degree celsius
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so that means what you are very well
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aware that practically
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each and every molecule of that room
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will not have the same temperature that
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is 25 degree celsius
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certain molecules will have 25.9 degree
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celsius
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24.9 degrees celsius 23 degree celsius
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26 degree celsius
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but in average they all are
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said to be having temperature of 25
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degree celsius so temperature can be
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defined as
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macroscopic property or microscopic
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approach right
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same way you can define the pressure
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also so this is
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how the microscopic and microscopic
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approach is
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taken this subject is dealing with in
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context of
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macroscopic approach only now next is
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thermodynamic system
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so as you can see over here a system is
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shown
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by simple oval shape now thermodynamic
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system
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is what it is the region is space upon
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which
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attention of focus is made that means
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what
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simple it is the area or volume upon
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which your
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attention is focused for the analysis of
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the problem that will be known as
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system for example you want to install
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an air conditioner in your bedroom
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so your bedroom volume or bedroom area
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that will be your system
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okay so that is how the system can be
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defined
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and everything except the system will be
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known as the
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surrounding right and system and
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surrounding
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the parting line between the system and
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surrounding
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that will be known as boundary now
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system and surrounding together will be
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known as
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universe and remember one thing
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surrounding is also known as
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environment right system and surrounding
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together will be known as
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universe right now there are
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certain classification of system that is
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known as types of system
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so thermodynamic system can be defined
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in different different types the very
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first is
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open system open system is also
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known as control volume system so let us
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understand what is the meaning of
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open system or control volume system so
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open system means
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symbol the mass as well as energy
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can transfer from the system to the
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surrounding
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or from the surrounding to the system
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vice versa will be the case
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right so that is what is called as open
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system
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right so for your understanding i have
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shown certain mechanical equipments
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that are known as open system right the
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very first is boiler
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the second is heat exchanger or
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condenser
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and the third is compressor so these all
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are open system
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why they are open system because as you
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can see the fluid will enter from
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the device and the fluid will leave from
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the device
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so mass is entering and mass is living
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that is why
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it is open system as well as the energy
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will also
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enter the system and energy will also
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leave the system
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right so in terms of heat that is why it
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is known as
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open system right now
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the next classification is isolated
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system
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so isolated system is what very simple
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neither mass
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nor energy can transfer from the system
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to the surrounding
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that will be known as isolated system
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now let us understand what is the
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meaning of isolated system
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okay simple uh let us take
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example of our universe so nothing can
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go
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beyond the universe neither mass nor
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energy
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or nothing can enter in the universe so
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that will be known as
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isolator system in some textbook
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thermos class is also taken as isolated
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system
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but you can consider it for a little
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time being
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right because it is a closed system if
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you take it
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on an exaggerated view right so isolated
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system
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the best example is what universe right
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now
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the last system that is closed system it
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is also known as controlled
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mass system so why this pro system
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simple why is this control mass system
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symbol the mass
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cannot transfer from the system to the
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surrounding or from the surrounding to
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the system
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but the energy can transfer from the
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system to the surrounding or vice versa
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right so that is why it is known as
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closed system
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right now no system examples are shown
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over here
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on the diagram of the screen the very
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first diagram is showing the
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vessel that is closed vessel and if the
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vessel is closed
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the lead is closed then the fluid cannot
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transfer from the vessel to the outside
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or the out from outside to the vessel
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another example is what i see engine so
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in ic engine as you can see
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particularly the second and third stroke
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that is what
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compression as well as expansion stroke
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during this strokes what will happen
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the mass cannot enter into the cylinder
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cavity
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or the mass cannot leave from the
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cylinder cavity so during these two
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strokes
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the mass is constant but energy can
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transfer from the system to the
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surrounding so that is why that will be
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known as
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example of closed system okay i hope it
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is clear to you guys
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now concept of continuum so very simple
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to understand
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concept of continuum means what so if
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you take any
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volume or any gas liquid or solid so we
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are very very aware
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that molecule size is very less so
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compared to molecular size the vessel
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size is very
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large right so what you can take is if
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you take one glass of water
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then in that one glass of water you will
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be having billions of h2o molecules
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present
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right so you can take that or you can
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consider that
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the h2o molecules are arranged in closed
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pack manner
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like this right so if you take
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that thing in consideration that will be
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known as
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continuum concept okay continuum concern
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means what
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your matter is distributed continuously
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and evenly
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throughout the substance that is known
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as continuum concept
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now it violates its validity when the
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mean free path
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reaches the magnitude of the level of
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the volume of the vessel
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now let us understand this typical
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statement now before understanding that
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we will have to understand what is the
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meaning of
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mean free path so let us understand mean
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free path
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very simple as you can see on the screen
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a yellow molecule is
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shown over here for your understanding
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now this yellow molecule
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will coincide or will collide with two
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surfaces the very first surface as you
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can see over here it will
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collide first with the bottom surface
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and then it will collide with the
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other molecule right so there are two
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collisions that are taking place
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so free path means what free path means
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the path travels between two
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successive collision that is known as
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free path
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so as you can see here the line that i
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have drawn that
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is nothing but the mean free path
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right now here
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mean free path means what simple you
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have to take mean
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of the all three paths together that
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will be known as mean free path
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now what is the violation of the
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continuous concept
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the variation of the continuum concept
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is that if the mean three path
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is having the magnitude equal to the
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magnitude of the
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volume of the vessel then you can take
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that
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it is violating the continuum concept
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right
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now let us understand certain
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definitions so for understanding the
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definition i have plotted pv diagram so
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i have taken pressure on the y axis and
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taken volume on the x-axis the very
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first
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definition is properties so what is the
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meaning of properties
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so in order to describe any physical
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condition of a substance
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you will require certain characteristics
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so that characteristics
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are known as properties for example if
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you want to define the hotness or
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coldness of a substance
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then you will require temperature so
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that temperature is nothing but the
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property
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now if the property has certain definite
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value
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then it will be known as state right
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so as you can see on the pv diagram i
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have plot one state
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so particular to this cross mark you
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will have a particular pressure value
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and you will have a particular volume
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value
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right on respectively y and x axis
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now if any operation is done in which
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one or more than one property is getting
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changed then it will be known as change
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of state
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so if you are moving from this cross
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mark to there is this cross mark
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then you can appreciate that the
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pressure and volume both will get
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changed
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so both properties are changing so that
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moving from
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first cross mark to the second cross
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mark
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that will be known as change of state
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now further
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path so succession of change of state
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will be known as path now if the path is
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completely defined
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so that will be known as process so for
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your understanding
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i have shown over here constant pressure
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process by a horizontal line
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so path is completely defined so that
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will be known as
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a particular process for example
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constant pressure process
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constant volume process then reversible
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adiabatic process
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isentropic process like that and if
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the two or more processes are occurring
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such that the initial state is identical
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with the final state
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then it will be known as cycle so here
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you can see
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from one to two and from two to back to
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one
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so the initial and final state both are
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one number
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so that this is known as site
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okay so today we are going keeping up to
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this point
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thank you
