Thermal Physics
Introduction
Thermal physics is a branch of physics that deals with the statistical nature of physical systems from an energetic perspective. It encompasses the laws of thermodynamics and statistical mechanics, which describe the behavior of macroscopic and microscopic systems, respectively.
Thermodynamics
Thermodynamics is the study of energy and its transformations. It is a macroscopic theory, as it does not require knowledge of the microscopic nature of matter. It involves the study of the relationships between heat, work, temperature, and energy. In thermodynamics, interactions between large ensembles of objects are studied and categorized, with no regard to the nature of individual objects in the system.
Laws of Thermodynamics
The laws of thermodynamics describe the specific ways in which thermal energy can be converted to other forms of energy and vice versa. They also define the fundamental physical quantities, such as temperature, energy, and entropy, that characterize thermodynamic systems.
Zeroth Law of Thermodynamics
The zeroth law of thermodynamics states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This law allows the definition of temperature in a non-circular way.
First Law of Thermodynamics
The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems. It states that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings.
Second Law of Thermodynamics
The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible. This is the principle of the increase of entropy.
Third Law of Thermodynamics
The third law of thermodynamics states that as a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.
Statistical Mechanics
Statistical mechanics provides a framework for relating the microscopic properties of individual atoms and molecules to the macroscopic or bulk properties of materials that can be observed in everyday life, therefore explaining thermodynamics as a result of statistics and mechanics (classical or quantum) at the microscopic level.
Microstates and Macrostates
In statistical mechanics, a microstate is a specific microscopic configuration of a thermodynamic system that the system may be in at a certain energy level. A macrostate, on the other hand, is characterized by a specific set of macroscopic properties, and may correspond to many different microstates of the system.
Boltzmann's Entropy Formula =
Boltzmann's entropy formula, S = k ln W, relates the entropy of an ideal gas to the quantity of real or phase space states available to it. Here, S is the entropy of the system, k is the Boltzmann constant, and W is the number of microstates corresponding to a given macrostate.
Partition Function =
The partition function is a function that expresses the statistical properties of a system in thermodynamic equilibrium. It is a sum over all states, weighted by the Boltzmann factor, e^(-E/kT), where E is the energy of the state, k is the Boltzmann constant, and T is the temperature.
Applications of Thermal Physics
Thermal physics has a wide range of applications, from industrial manufacturing to biological systems. It is used in the design and analysis of heat engines, refrigerators, and heat pumps. It also plays a crucial role in understanding and controlling the thermal properties of materials, and in the study of stellar structure and the early universe.