Contents
With new discoveries and innovations constantly being made, the study of Physics Topics remains a vibrant and exciting field of research.
What are the Properties of Thermodynamics?
Introduction
Position, displacements velocity, acceleration, etc. are external properties of a body From them, we get no information about the naure of the body. They are discussed in the subject of mechanics.
On the other hand, properties like mass (M), volume (V), pressure (p), temperature (T), density (ρ), etc., are internal properties of a body. These are bulk (macroscopic) properties and can be measured by simple experiments. Any change in these properties generally involves transfer of energy in the form of heat or work. All of these are studied in a branch of physics, known as thermodynamics. The above mentioned properties and similar others are called thermodynamic properties.
The subject is based only on experimental data and every thermodynamic formula comes from the analysis of this data. For example, suppose a fixed mass of an ideal gas is studied at constant temperature. Any change of pressure produces a change in volume and different sets of p and V are obtained. An analysis of these measured values shows that the product pV = constant. This is the well-known Boyle’s law. As it is experiment based, it is a thermodynamic law.
Thermodynamic Systems
A body or a part of a body, or a combination of a number of bodies which is being studied is usually called a thermodynamic system. In general, such a system interacts with its surroundings or, environment and exchanges energy and mass. The environment or surroundings includes all external objects that have some influence on the system. For example, if a room in a house is considered as a system and its thermal properties are to be studied, the sun at a distance of 1.5 × 108km is an important component of the environment, but another house only 100m away need not be included as a component. Thermodynamic systems are of three types.
Isolated system: This system does not exchange any energy or mass with the surroundings.
Closed system: Energy is exchanged with the surroundings, but the mass remains fixed.
Open system: Both energy and mass are exchanged. We shall not discuss open systems in this chapter.
Properties like number of molecules, molecular velocity, etc., are internal microscopic properties of a body. They are not directly measurable and experimental data is absent. Hence, the study of this subject is based on the theoretical assumptions and is known as kinetic theory (see the chapter kinetic Theory of Gases).
Nature of Heat
Heat is a form of energy which can be identified only when it is in transit. It can be converted into other forms of energy and vice versa. To measure the amount of heat energy, different units are used:
In SI, the unit of energy is directly used to measure some quantity of heat. So, Joule (J) is the unit of heat in SI, as it is the SI unit of energy. Similarly, other energy units like erg may also be used.
Immediately it becomes clear that the energy units must have definite relations with the conventional units of heat. This topic is discussed in the next section.
In thermodynamics, the definition of temperature comes earlier from the zeroth law of thermodynamics (see the chapter Thermometry. The definition of heat is based on the concept of temperature.
Definition: Heat is a form of energy which is transmitted from one place to another due to their temperature differences only.
It is interesting to note the difference between this and the calorimetric definition of heat (see the chapter Thermometry).