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THERMAL PHYSICS презентация, доклад

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Learning Objectivesunderstand and apply first law of thermodynamicsdistinguish graphs of adiabatic and isothermal processesunderstand second law of thermodynamics

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Слайд 1THERMAL PHYSICS

THERMAL PHYSICS

Слайд 2Learning Objectives
understand and apply first law of thermodynamics
distinguish graphs of

adiabatic and isothermal processes
understand second law of thermodynamics

Learning Objectivesunderstand and apply first law of thermodynamicsdistinguish graphs of adiabatic and isothermal processesunderstand second law of

Слайд 3Terms to Remember!
Thermodynamics
Thermodynamic System
Surroundings
Heat
Work
Internal Energy

Terms to Remember!ThermodynamicsThermodynamic SystemSurroundingsHeatWorkInternal Energy

Слайд 4Thermodynamics
Thermodynamics is the macroscopic study of the behaviour of systems.

It was a mathematical theory developed before a detailed understanding

of the particulate nature of gases.
ThermodynamicsThermodynamics is the macroscopic study of the behaviour of systems. It was a mathematical theory developed before

Слайд 5Thermodynamic System
Thermodynamic System is a macroscopic aspect of a problem

than can be considered as a separate whole. An ideal

gas for example can have energy flowing in or out of it from
the surroundings.
Thermodynamic SystemThermodynamic System is a macroscopic aspect of a problem than can be considered as a separate

Слайд 6Surroundings
Surroundings is everything in the problem outside the
thermodynamic system.

Heat can flow from the system to the surroundings and

vice versa.
SurroundingsSurroundings is everything in the problem outside the thermodynamic system. Heat can flow from the system to

Слайд 7Surroundings

Surroundings

Слайд 8Thermodynamic Systems

Thermodynamic Systems

Слайд 9Isolated System

Isolated System

Слайд 10Closed System

Closed System

Слайд 11Open System

Open System

Слайд 12Heat
Heat (Q) is an amount of thermal energy transferred from

the surroundings to an ideal gas. It is a result

of a temperature difference.
HeatHeat (Q) is an amount of thermal energy transferred from the surroundings to an ideal gas. It

Слайд 13Heat Flow (Review)

Heat Flow (Review)

Слайд 14Work
Work (W) is simply a macroscopic transfer of energy from

the gas to the surroundings.

WorkWork (W) is simply a macroscopic transfer of energy from the gas to the surroundings.

Слайд 21Change in Internal Energy
Change in Internal Energy (∆U) is the

change in a gas’ energy due to the PE and

KE of the molecules.
It does not include external factors such as gravity.
∆U for an ideal gas will involve temperature changes (∆θ).
Change in Internal EnergyChange in Internal Energy (∆U) is the change in a gas’ energy due to

Слайд 22Change in Internal Energy
The change in internal energy (ΔU) of

a closed system will be equal to the energy added

to the system by heating minus the work done by the system on the surroundings.
ΔU = Q – W
Change in Internal EnergyThe change in internal energy (ΔU) of a closed system will be equal to

Слайд 231st Law of Thermodynamics
The First Law of Thermodynamics states that

when heat Q is added to a system while the

system does work W, the internal energy U changes by an amount equal to Q – W.
ΔU = Q – W
1st Law of ThermodynamicsThe First Law of Thermodynamics states that when heat Q is added to a

Слайд 241st Law of Thermodynamics
Since Q and W represent energy transferred

into or out of the system , the internal energy

changes accordingly.
The First Law of Thermodynamics is great and broad statement of the law of conservation of energy.
1st Law of ThermodynamicsSince Q and W represent energy transferred into or out of the system ,

Слайд 251st Law of Thermodynamics
The internal energy of any thermodynamic system

depends only on its state. The change in internal energy

in any process depends only on the initial and final states, not on the path.
The internal energy of an isolated system is constant.
1st Law of ThermodynamicsThe internal energy of any thermodynamic system depends only on its state. The change

Слайд 26State
State is defined as the physical condition of the system.

StateState is defined as the physical condition of the system.

Слайд 27Important Note
A given system at any moment is in particular

state and can be said to have a certain amount

of internal energy.
But a system does NOT have a certain amount of heat or work.
Important NoteA given system at any moment is in particular state and can be said to have

Слайд 28Important Note
Rather, when work is done on a system or

when heat is added or removed from a system, the

state of the system changes.
Important NoteRather, when work is done on a system or when heat is added or removed from

Слайд 29Important Note
Thus, work and heat are involved in thermodynamic processes

that can change the system from one state to another;

they are not characteristic of the state itself.
Important NoteThus, work and heat are involved in thermodynamic processes that can change the system from one

Слайд 30State Variables
Quantities which describe the state of the system is

called state variables.
Internal Energy (U) Mass (m)
Pressure (P) Volume (V)
Temperature (T)


Number of Moles (n)
State VariablesQuantities which describe the state of the system is called state variables.Internal Energy (U)		 Mass (m)Pressure

Слайд 31Sample Problem
2500 J of heat is added to a system,

and 1800 J of work is done on the system.

What is the change in internal energy of the system?
Sample Problem2500 J of heat is added to a system, and 1800 J of work is done

Слайд 32Sample Problem
2500 J of heat is added to a system,

and 1800 J of work is done by the system.

What is the change in internal energy of the system?
Sample Problem2500 J of heat is added to a system, and 1800 J of work is done

Слайд 33Isothermal Process and 1st Law of Thermodynamics
To analyze some thermodynamic

process in light of the 1st law of thermodynamics, consider

a fixed mass of an ideal gas enclosed in a container fitted with movable piston.
Isothermal Process and 1st Law of ThermodynamicsTo analyze some thermodynamic process in light of the 1st law

Слайд 34Isothermal Process and 1st Law of Thermodynamics
Consider an idealized process

that is carried out at constant temperature. Such process is

called isothermal process.
If an isothermal process is carried out on our ideal gas, then
PV = nRT becomes PV = constant.
Isothermal Process and 1st Law of ThermodynamicsConsider an idealized process that is carried out at constant temperature.

Слайд 35Isothermal Process and 1st Law of Thermodynamics
The process follows a

curve like AB on the PV diagram, which is a

curve for PV = constant.

PV Diagram for an ideal gas undergoing isothermal process at two different temperatures

Isothermal Process and 1st Law of ThermodynamicsThe process follows a curve like AB on the PV diagram,

Слайд 36Isothermal Process and 1st Law of Thermodynamics
Each point on the

curve, such as point A, represents a state of the

system – that is, its pressure P and volume V at a given moment.

PV Diagram for an ideal gas undergoing isothermal process at two different temperatures

Isothermal Process and 1st Law of ThermodynamicsEach point on the curve, such as point A, represents a

Слайд 37Isothermal Process and 1st Law of Thermodynamics
The curves shown are

referred to as isotherms.
PV Diagram for an ideal gas undergoing

isothermal process at two different temperatures
Isothermal Process and 1st Law of ThermodynamicsThe curves shown are referred to as isotherms.PV Diagram for an

Слайд 38Work Done
In the process A to D, the gas does

no work since the volume does not change
(isochoric).

Work DoneIn the process A to D, the gas does no work since the volume does not

Слайд 39Work Done
Going from D to B, the gas does work

equal to
PB(VB – VA).
This is the total work done in

the process ADB.
(isobaric)
Work DoneGoing from D to B, the gas does work equal toPB(VB – VA).This is the total

Слайд 40Work Done
If the pressure varies during a process, such as

for the isothermal process A,
W = PΔV
cannot be used directly

to determine the work.
Work DoneIf the pressure varies during a process, such as for the isothermal process A,W = PΔVcannot

Слайд 41Work Done
The calculation of work done (WAB) in this case

can be carried out using calculus, or by estimating the

area under the curve.
Work DoneThe calculation of work done (WAB) in this case can be carried out using calculus, or

Слайд 42Adiabatic Process and 1st Law of Thermodynamics
An adiabatic process is

one in which no heat is allowed to flow into

or out of the system: Q = 0.
This situation can occur if the system is extremely well insulated, or the process happens so quickly that heat – which flows slowly – has no time to flow in or out.
Adiabatic Process and 1st Law of ThermodynamicsAn adiabatic process is one in which no heat is allowed

Слайд 43Adiabatic Process and 1st Law of Thermodynamics
The very rapid expansion

of gases in an internal combustion engine is one example

of a process that is very nearly adiabatic.
Adiabatic Process and 1st Law of ThermodynamicsThe very rapid expansion of gases in an internal combustion engine

Слайд 44Adiabatic Process and 1st Law of Thermodynamics
A slow adiabatic expansion

of an ideal gas follows a curve like that labelled

AC in the PV diagram shown.
Adiabatic Process and 1st Law of ThermodynamicsA slow adiabatic expansion of an ideal gas follows a curve

Слайд 45Adiabatic Process and 1st Law of Thermodynamics
Since Q = 0,

then ΔU = –W.
That is, the internal energy decreases if

the gas expands; hence the temperature decreases as well because
Adiabatic Process and 1st Law of ThermodynamicsSince Q = 0, then ΔU = –W.That is, the internal

Слайд 46Adiabatic Process and 1st Law of Thermodynamics
In the reverse operation,

an adiabatic compression, work is done on the gas, and

hence the internal energy increases and the temperature rises.
Adiabatic Process and 1st Law of ThermodynamicsIn the reverse operation, an adiabatic compression, work is done on

Слайд 47Thermodynamic Process and 1st Law of Thermodynamics

Thermodynamic Process and 1st Law of Thermodynamics

Слайд 48Sample Problem:
An ideal gas is slowly compressed at a constant

pressure of 2.0 atm from 10.0 L to 2.0 L.

Calculate (a) the total work done by the gas in the process BDA, and (b) the total heat flow into the gas.
Sample Problem:An ideal gas is slowly compressed at a constant pressure of 2.0 atm from 10.0 L

Слайд 50Sample Problem:
In an engine, 0.25 moles of an ideal monatomic

gas in the cylinder expands rapidly and adiabatically against the

piston. In the process, the temperature of the gas drops from 1150 K to 400 K. How much work does the gas do?
Sample Problem:In an engine, 0.25 moles of an ideal monatomic gas in the cylinder expands rapidly and

Слайд 52Sample Problem:
A gas in a container with a piston expands

isothermally. If thermal energy Q = 105 is given to

the gas, what is the work done by the gas?
Sample Problem:A gas in a container with a piston expands isothermally. If thermal energy Q = 105

Слайд 54Sample Problem:
A gas expands adiabatically. Will its temperature increase or

decrease?

Sample Problem:A gas expands adiabatically. Will its temperature increase or decrease?

Слайд 56Sample Problem:
A monatomic gas is kept at constant pressure 3.00

× 106 Pa, initial volume 0.100 m3 and temperature 300

K. If the gas is compressed at constant pressure down a volume of 0.800 m3, find:
(a) the work done on the gas; (b) the thermal energy taken out of the gas.
Sample Problem:A monatomic gas is kept at constant pressure 3.00 × 106 Pa, initial volume 0.100 m3

Слайд 582nd Law of Thermodynamics
There are many processes in thermodynamics that

are consistent with the first law but are nonetheless impossible.

2nd Law of ThermodynamicsThere are many processes in thermodynamics that are consistent with the first law but

Слайд 592nd Law of Thermodynamics
If you put a layer of salt

in a jar and cover it with a layer of

similar-sized grains of pepper, when you shake it you get a thorough mixture. But no matter how long you shake it, the mixture does not separate into layers again.
2nd Law of ThermodynamicsIf you put a layer of salt in a jar and cover it with

Слайд 602nd Law of Thermodynamics
Coffee cups and glasses break spontaneously if

you drop them. But they don’t go back together spontaneously.
The

spontaneous (without the action of another agent) transfer of thermal energy from a cold body to hotter body


2nd Law of ThermodynamicsCoffee cups and glasses break spontaneously if you drop them. But they don’t go

Слайд 612nd Law of Thermodynamics
The air in a room suddenly occupying

just one half of the room and leaving the other

half empty.
A glass of water at room temperature suddenly freezing, causing the temperature of the room to rise

2nd Law of ThermodynamicsThe air in a room suddenly occupying just one half of the room and

Слайд 622nd Law of Thermodynamics
These processes do not open happen because

they are forbidden by a very special law of physics

– the second law of thermodynamics.
2nd Law of ThermodynamicsThese processes do not open happen because they are forbidden by a very special

Слайд 632nd Law of Thermodynamics
The 1st law of thermodynamics (conservation of

energy) would not be violated any of these processes.
To explain

this lack of reversibility, scientists in the latter half of the 19th century formulated a new principle known as the 2nd law of thermodynamics.
2nd Law of ThermodynamicsThe 1st law of thermodynamics (conservation of energy) would not be violated any of

Слайд 642nd Law of Thermodynamics
The second law of thermodynamics describes the

directionality of natural thermodynamic processes.
It can be stated in several

equivalent forms.
2nd Law of ThermodynamicsThe second law of thermodynamics describes the directionality of natural thermodynamic processes.It can be

Слайд 652nd Law of Thermodynamics
According to Rudolf J.E. Clausius (1822 –

1888)
“heat can flow spontaneously from a hot object to a

cold object ; heat will not flow spontaneously from a cold object to a hot object”
2nd Law of ThermodynamicsAccording to Rudolf J.E. Clausius (1822 – 1888)“heat can flow spontaneously from a hot

Слайд 662nd Law of Thermodynamics
The engine statement is that “no cyclic

process can convert heat completely into work”.

2nd Law of ThermodynamicsThe engine statement is that “no cyclic process can convert heat completely into work”.

Слайд 672nd Law of Thermodynamics
The refrigerator statement is that “no cyclic

process can transfer heat from a colder place to a

hotter place with no input of mechanical work”.
2nd Law of ThermodynamicsThe refrigerator statement is that “no cyclic process can transfer heat from a colder

Слайд 682nd Law of Thermodynamics
The development of a general statement of

the second law of thermodynamics was based partly on the

study of heat engines.
2nd Law of ThermodynamicsThe development of a general statement of the second law of thermodynamics was based

Слайд 692nd Law of Thermodynamics
A heat engine is any device that

changes thermal energy into mechanical work, such as steam engines

and automobile engines.
2nd Law of ThermodynamicsA heat engine is any device that changes thermal energy into mechanical work, such

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