Physics
Thermal Physics
Thermal physics is the study of heat and temperature and their effects on matter. It explores the behavior of atoms and molecules in response to thermal energy, as well as the transfer of heat through various processes such as conduction, convection, and radiation. This field also encompasses the laws of thermodynamics, which govern the behavior of thermal systems.
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12 Key excerpts on "Thermal Physics"
eBook - PDFTheoretical Concepts in Physics
An Alternative View of Theoretical Reasoning in Physics
- Malcolm S. Longair(Author)
- 2020(Publication Date)
- Cambridge University Press(Publisher)
Case Study IV THERMODYNAMICS AND STATISTICAL PHYSICS Thermodynamics is the science of how the properties of matter and systems change with temperature. The system may be viewed on the microscopic scale, in which case we study the interactions of atoms and molecules and how these change with temperature. In this approach, we need to construct physical models for these interactions. The opposite approach is to study the system on the macroscopic scale and then the unique status of classical thermodynamics becomes apparent. In this approach, the behaviour of matter and radiation in bulk is studied and we quite explicitly deny that they have any internal structure at all. In other words, the science of classical thermodynamics is solely concerned with relations between macroscopic measurable quantities. Now this may seem to make classical thermodynamics a rather dull subject but, in fact, it is quite the opposite. In many physical problems, we may not know in detail the correct microscopic physics, and yet the thermodynamic approach can provide answers about the macroscopic behaviour of the system which is independent of the unknown detailed microphysics. Another way of looking at the subject is to think of classical thermodynamics as providing the boundary conditions which any microscopic model must satisfy. The thermodynamic arguments have validity independent of the model adopted to explain any particular phenomenon. It is remarkable that these profound statements can be made on the basis of the two laws of thermodynamics. Let us state them immediately. The first law of thermodynamics is a statement about the conservation of energy: Energy is conserved when heat is taken into account. The second law of thermodynamics tells us how thermodynamic systems evolve with time. This can be deduced from the statement of the law due to Clausius: No process is possible whose sole result is the transfer of heat from a colder to a hotter body.
eBook - PDFStatistical and Thermal Physics
An Introduction
- Michael J.R. Hoch(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
C H A P T E R 1 Introduction: Basic Concepts 1.1 STATISTICAL AND Thermal Physics Thesubjectofstatisticalandthermalphysicsisconcernedwiththedescrip-tion of macroscopic systems made up of large numbers of particles of the order of Avogadro’s number N A = 6.02 × 10 23 mol –1 . The particles may be atomsormoleculesingases,liquids,andsolidsorsystemsofsubatomicpar-ticlessuchaselectronsinmetalsandneutronsinneutronstars.Arichvari-etyofphenomenaareexhibitedbymany-particlesystemsofthissort.The concepts and relationships that are established in Thermal Physics provide thebasisfordiscussionofthepropertiesofthesesystemsandtheprocesses in which they are involved. Applications cover a wide range of situations, frombasicscience,inmanyimportantfieldsthatincludecondensedmatter physics,astrophysics,andphysicalchemistrytopracticaldevicesinenergy technology. Theoriginsofmodernthermalphysicsmaybetracedtotheanalysisof heatenginesinthenineteenthcentury.Followingthisearlyworkanum-berofresearcherscontributedtothedevelopmentofthesubjectofther-modynamicswithitsfamouslaws.Bytheendofthenineteenthcentury, thermodynamics,classicalmechanics,andelectrodynamicsprovidedthe foundationforallofclassicalphysics.Todaythermodynamicsisawell-developedsubject,withmodernresearchfocusedonspecialtopicssuchas nonequilibriumthermodynamics.Applicationofthemethodsofthermo-dynamicstocomplexsystemsfarfromequilibrium,whichincludeliving organisms,presentsamajorchallenge. 5
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
As a system receives heat, its temperature rises; similarly, a loss of heat from the system decreases its temperature. When two systems are at the same temperature, no heat transfer occurs between them. When a temperature difference does exist, heat will transfer from the warmer system to the colder system, until they are at thermal equilibrium. This transfer occurs via heat conduction. Statistically, temperature ( T ) is a direct measure of the mean kinetic energy of the particles forming a sample of matter. For each degree of freedom that a particle possesses, the mean kinetic energy ( E k ) of the particles is: , where k is the Boltzmann constant, a fixed proportionality factor introduced by the system of units used to measure energy and temperature. Macroscopically, temperature is related to the amount of internal energy and enthalpy of a system: the higher the temperature of a system, the higher its internal energy and enthalpy. For a system in thermal equilibrium at a constant volume, temperature is thermodynamically defined in terms of its energy ( E ) and entropy ( S ) as: ____________________ WORLD TECHNOLOGIES ____________________ Temperature is an intensive property of a system, meaning that it does not depend on the system size, the amount or type of material in the system, the same as for the pressure and density. By contrast, mass, volume, and entropy are extensive properties, and depend on the amount of material in the system. Heat capacity When a sample is heated, meaning it receives thermal energy from an external source, some of the introduced heat is converted into kinetic energy, the rest to other forms of internal energy, specific to the material. The amount converted into kinetic energy causes the temperature of the material to rise. The introduced heat ( Δ Q ) divided by the observed temperature change is the heat capacity ( C ) of the material.
eBook - ePub- Charles Liu(Author)
- 2020(Publication Date)
- Visible Ink Press(Publisher)
THERMODYNAMICS
What is thermodynamics?
Thermodynamics is the study of the change of thermal energy in objects and materials that makes them warm and cold, how they interact with each other, and the relationship between energy, heat, and work. It can be a challenging area of physics, in part because most of the vocabulary dates from the time before scientists understood what makes an object hot. Terms like “heat,” “heat capacity,” and “latent heat” suggest that warm objects contain some material that reacts to temperature. It wasn’t until the early 1800s that our present understanding started to develop. Some 200 years later, our common usage of these terms is still based on earlier ideas.What is thermal energy?
Thermal energy is the random kinetic energy of the moving particles—such as atoms and molecules—that make up matter. Objects expand when heated, so the bonds holding the particles together stretch. That means they have more elastic energy. So, thermal energy is the sum of the kinetic and elastic energy of the atoms and molecules and the bonds that hold them together. It is energy that is inside the object, so it is called a form of internal energy.Thermal Physics
Who discovered what makes an object hot?
Benjamin Thompson, Count Rumford (1753–1814), who was born in the Massachusetts Bay Colony but did most of his scientific work in the Kingdom of Bavaria (which is now part of Germany), deserves a great deal of credit in discovering what makes things hot. Before his experiments, most scientists thought that hot objects contained an invisible fluid called caloric. Experiments done before Rumford showed that when you heated an object it didn’t gain weight, so caloric must be weightless as well as invisible. This result made many scientists suspicious of the caloric explanation.In 1789 Rumford drilled holes in bronze cannons through which a cannonball would be shot. He found that both the cannon and the metal chips that resulted from the drilling became hot. He determined the amount of water that could be raised to the boiling point by both the cannon bodies and the chips and showed that the caloric theory did not agree with his results. He finally concluded that in hot objects, the particles that made up the material moved faster than they moved in cold objects. Using our present terminology, they had more kinetic energy. In their motion they vibrate back and forth; they do not move together from one place to another like a thrown ball.
eBook - PDF- Stephen McKnight, Christos Zahopoulos(Authors)
- 2015(Publication Date)
- Cambridge University Press(Publisher)
Temperature, in short, is a measure of the average internal energy of the particles of a system. Heat, on the other hand, is a measure of the total energy added to or transferred away from a system. A larger system can have more total energy available than a smaller system at a higher temperature. 12.4 Equation of state In a molecular picture of materials, a complete description of a system would be to specify the exact position and momentum of each molecule. Such a specification would be mind-boggling complex, and in addition it would need to be updated every instant of time as the molecules of the material interact and are accelerated by intermolecular forces and interactions with the system container. Instead, we seek to find a set of macroscopic parameters that can describe the properties of the system in a state of thermal equilibrium. We understand that there will be statistical fluctuations of the system around the equilibrium values – and we can even calculate how large these fluctuations will be – but the implicit assumption is that these fluctuations will become vanishingly small as the system becomes large. This assumption is, in fact, confirmed both by calculation and by empirical measurements. If the system we are considering is a gas or liquid which conforms to the shape of the container, the set of parameters that we need to describe the system would include the number of molecules n, the volume of the system V, the pressure the molecules exert on any internal or container surface P, and the temperature of the system (expressed in degrees kelvin) T. These parameters are not all independent – they are related by an equation of state which depends on the details of the intermolecular forces as well as any external forces, such as the gravitational force on the molecules. If the system is a solid, we would also have to specify the crystal structure of the molecules and any internal shear stresses.
eBook - PDFEngineering Problem Solving
A Classical Perspective
- Milton C. Shaw(Author)
- 2001(Publication Date)
- William Andrew(Publisher)
Thermal Engineering 269 269 1.0 INTRODUCTION Important topics to be considered in this chapter are thermodynamics, thermal transformation systems, and heat transfer. Thermodynamics in-volves fundamental relationships between heat, work, and the properties of a system. It is concerned with the transformation of one form of energy into another and the basic laws that control such transformation. Of particular importance is the transformation of thermal energy into mechani-cal energy, which is the first step in the conversion of the energy associated with fossil fuels into electrical energy as discussed in Ch. 10. Thermal transformation systems are systems that transform thermal energy into mechanical energy. This includes steam power plants, steam engines, steam turbines, gas turbines, and internal combustion engines. Heat trans-fer is concerned with the transfer of thermal energy from one medium to another by: Radiation Conduction Convection 11 Thermal Engineering 270 Engineering Problem Solving: A Classical Perspective With radiation, heat is transferred by electromagnetic waves ema-nating from a hot body to a cold body where radiation waves are absorbed resulting in a temperature rise. Conductive heat transfer involves the passage of heat through a solid from a region of high temperature to one of lower temperature. Convective heat transfer involves the transport of thermal energy from a hot body to a fluid flowing across the hot body. 2.0 HISTORICAL BACKGROUND Before the 17 th century, little attention was given to thermal energy. The Phlogiston Theory of heat championed by Stahl (16601734) was the first generally accepted. This proposed that all combustible materials contain a massless material (phlogiston) that escapes on combustion. Some materials like sulfur were considered rich in phlogiston while others con-tained very little.
eBook - PDF- Ethirajan Rathakrishnan(Author)
- 2012(Publication Date)
- CRC Press(Publisher)
Chapter 1 Basic Concepts and Definitions 1.1 Introduction Heat transfer is the science of energy transfer due to a temperature differ-ence. We know that thermodynamics deals with energy balance in a variety of physical situations. In other words, thermodynamics deals with the amount of heat transfer as a system undergoes a process from one equilibrium state to another. Heat transfer, on the other hand, deals with the rate at which heat is transferred as well as the temperature distribution within the system as a function of time. Basically thermodynamics deals with systems in equi-librium. It may be used to predict the amount of thermal energy required to change a system from one thermal equilibrium state to another. But it can-not predict how fast this change from one equilibrium state to another will take place, because the system is not in equilibrium during the process. For example, consider the cooling of a hot metallic bar placed in a water bath. Thermodynamics may be used to predict the final equilibrium temperature of the metallic bar-water combination. But thermodynamics cannot answer the question, how long the process would take to reach this equilibrium or what would be the temperature of the bar after a certain time interval before the equilibrium is attained? Whereas, the science of heat transfer can answer these questions. That is, heat transfer can predict the temperature of both the metal bar and the water as a function of time. In other words, unlike ther-modynamics, heat transfer can answer the transient energy transfer questions such as the following: • Can heat be supplied to a system without employing high temperature difference? • How long would it take to supply a certain amount of heat energy to the 1
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
temperature of a particular substance, showing at which pressures and temperatures the phases of the substance occur Chapter 1 | Temperature and Heat 53 radiation rate of conductive heat transfer specific heat Stefan-Boltzmann law of radiation sublimation temperature thermal conductivity thermal equilibrium thermal expansion thermal stress triple point vapor vapor pressure zeroth law of thermodynamics energy transferred by electromagnetic waves directly as a result of a temperature difference rate of heat transfer from one material to another amount of heat necessary to change the temperature of 1.00 kg of a substance by 1.00 °C ; also called “specific heat capacity” P = σAeT 4 , where σ = 5.67 × 10 −8 J/s · m 2 · K 4 is the Stefan-Boltzmann constant, A is the surface area of the object, T is the absolute temperature, and e is the emissivity phase change from solid to gas quantity measured by a thermometer, which reflects the mechanical energy of molecules in a system property of a material describing its ability to conduct heat condition in which heat no longer flows between two objects that are in contact; the two objects have the same temperature change in size or volume of an object with change in temperature stress caused by thermal expansion or contraction pressure and temperature at which a substance exists in equilibrium as a solid, liquid, and gas gas at a temperature below the boiling temperature pressure at which a gas coexists with its solid or liquid phase law that states that if two objects are in thermal equilibrium, and a third object is in thermal equilibrium with one of those objects, it is also in thermal equilibrium with the other object KEY EQUATIONS Linear thermal expansion ΔL = αLΔT Thermal expansion in two dimensions ΔA = 2αAΔT Thermal expansion in three dimensions ΔV = βV ΔT Heat transfer Q = mcΔT Transfer of heat in a calorimeter Q cold + Q hot = 0 Heat due to phase change (melting and freezing) Q = mL f Heat due to phase change (evaporation and condensation) Q = mL v Rate of conductive heat
- Raymond Serway, John Jewett(Authors)
- 2018(Publication Date)
- Cengage Learning EMEA(Publisher)
Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 484 Chapter 18 Temperature We can summarize these results in a statement known as the zeroth law of ther- modynamics (the law of equilibrium): If objects A and B are separately in thermal equilibrium with a third object C, then A and B are in thermal equilibrium with each other. Zeroth law of thermodynamics This statement can easily be proved experimentally and is very important because it enables us to define temperature. We can think of temperature as the property that determines whether or not energy will transfer between two objects when they are in thermal contact. Two objects in thermal equilibrium with each other are at the same temperature. Conversely, if two objects have different temperatures, they are not in thermal equilibrium and energy will transfer between them when they are placed in thermal contact. In Figure 18.1, it is only the temperatures of A and B that determine whether energy will transfer from one to the other when they are placed in thermal contact—not size , mass, material , density, or anything else. For now, temperature is only defined for us in terms of the zeroth law. We will relate temperature to molecular motion in Chapter 20. Q UICK QUIZ 18.1 Two objects, with different sizes, masses, and tempera- tures, are placed in thermal contact. In which direction does the energy travel? (a) Energy travels from the larger object to the smaller object. (b) Energy travels from the object with more mass to the one with less mass.
eBook - PDF- P R Wallace(Author)
- 1991(Publication Date)
- World Scientific(Publisher)
I have named the general law the principle of the conservation of energy. This law, which is sometimes also called the first law of thermodynamics, has subsequently become a keystone of all physics; no physical principle carries more authority. That this was not so in Helmholtz's time is evident from the fact that the most prestigious physics journal of the time, the Annalen der Physik, rejected for publication the article in which Helmholtz enunciated this principle. The law has, however, been modified in the light of Einstein's prin-ciple that matter itself was energy (the famous E = mc 2 ). Contrary Heat and Thermodynamice 267 to Helmholtz' formulation, we now know that the quantity of energy is not as unalterable as the quantity of matter; rather, it is the two together which are conserved and unalterable. 11.3. What is Temperature? When we speak of temperature, we think of an instrument which measures it, for example, a mercury thermometer. But why do we believe that the length of a column of mercury is a reasonable mea-sure of how hot things are, that is, how much heat energy they contain? If we add heat energy to the mercury column, it expands. By careful measurement, we can even verify that the amount of the expansion is proportional to the amount of heat added, within lim-its. The expansion, therefore, can give us a linear scale of heat con-tent. Note that the significance of the temperature scale depends on an empirically verifiable law. The question of whether the mercury thermometer is the Jest measure of heat energy is open. It is conceiv-able that other physical phenomena are more accurately correlated with heat content (the voltage in a thermocouple, for example), and therefore more accurate thermometers, but this is simply a technical question. 11.4. The Law of Gay-Lussac and Charles A second phenomenon embodied in a statistical law for gases is associated with the names Gay-Lussac and Charles.
eBook - PDF- Steven Weinberg(Author)
- 2021(Publication Date)
- Cambridge University Press(Publisher)
2.4 Kinetic Theory and Statistical Mechanics 33 in Eq. (2.3.1) must converge. This has the consequence, in particular, that the specific heat dQ/dT must vanish for T → 0. This seems to contradict the results of Section 2.1 for ideal gases, which give a temperature-independent specific heat whether for fixed volume or fixed pressure. The contradiction is avoided in practice because no substance remains close to an ideal gas as the temperature approaches absolute zero. We will see when we come to quantum mechanics that if an otherwise free particle is confined in any fixed volume, then it cannot have precisely zero momentum, as required for a classical ideal gas at absolute zero temperature. On the other hand, solids can exist at absolute zero temperature, and in that limit their specific heats do approach zero. 2.4 Kinetic Theory and Statistical Mechanics We saw in the previous chapter how by the mid nineteenth century the ideal gas law had been established through the work especially of Bernoulli and Clausius. But, though derived by considering the motions of individual gas molecules, in its conclusions it dealt only with bulk gas properties such as pressure, tem- perature, mass density, and energy density. For many purposes, including the calculation of chemical or transport processes, it was necessary to go further and work out the detailed probability distribution of the motion of individual gas particles. This was done in the kinetic theory of James Clerk Maxwell and Ludwig Boltzmann (1844–1906). Kinetic theory was later generalized to the formalism known as statistical mechanics, especially by the American theorist Josiah Willard Gibbs (1839–1906). As it turned out, these methods went a long way toward not only establishing a correspondence with thermodynamics but also explaining the principles of thermodynamics on the assumption that macroscopic matter is composed of very many particles, and thereby helping to establish the reality of atoms.
eBook - PDF- Raymond Serway, Chris Vuille(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
In this section we take a closer look at heat as a means of energy transfer and consider the processes of thermal conduction, convection, and radiation. 11.5.1 Thermal Conduction The energy transfer process most closely associated with a temperature differ- ence is called thermal conduction or simply conduction. In this process the trans- fer can be viewed on an atomic scale as an exchange of kinetic energy between microscopic particles—molecules, atoms, and electrons—with less energetic particles gaining energy as they collide with more energetic particles. An inex- pensive pot, as in Figure 11.4, may have a metal handle with no surrounding insulation. As the pot is warmed, the temperature of the metal handle increases, and the cook must hold it with a cloth potholder to avoid being burned. The way the handle warms up can be understood by looking at what happens to the microscopic particles in the metal. Before the pot is placed on the stove, the particles are vibrating about their equilibrium positions. As the stove coil warms up, those particles in contact with it begin to vibrate with larger amplitudes. These particles collide with their neighbors and transfer some of their energy in the collisions. Metal atoms and electrons farther and farther from the coil gradu- ally increase the amplitude of their vibrations, until eventually those in the handle (c) Estimate the pressure of the gas, using the ideal gas law. First, compute the number of moles of steam: n 5 1 4.80 3 10 11 kg 2a 1 mol 0.018 kg b 5 2.67 3 10 13 mol Solve for the pressure, using PV 5 nRT : P 5 nRT V 5 1 2.67 3 10 13 mol 21 8.31 J/mol # K 21 3.98 3 10 5 K 2 5.23 3 10 8 m 3 P 5 1.69 3 10 11 Pa REMARKS The estimated pressure is several hundred times greater than the ultimate shear stress of steel! This high-pressure region would expand rapidly, destroying everything within a very large radius.
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