CONCEPT MAP OF THERMAL PHYSICS
Structural Communication Topic:
The title "Thermal Physics" has been chosen to emphasize a broad concern with thermal behaviour. What can be called the "thermal concepts" have a relevance to many branches of physics, to chemistry, and also to biology. These concepts also have a powerful role to play in the integration of the sciences in a course of study.
Thermal physics can be seen as an attempt to link together thermal and mechanical behaviour; it extends into molecular theories, statistics and quantum mechanics. Right from the beginning there should be established a sense for the methods which link thermal and mechanical phenomena. This is why it is imperative that, at least in the sixth form, students are enabled to see more clearly the characteristic limitations of thinking in terms of the calorie and empirical temperature.
In order to bring temperature into line with the mechanical parameters of systems, such as pressure and volume, the parameter of entropy has to be introduced. Temperature and entropy then form a thermal plane of representation which complements the mechanical one. In this topic book, the notion of two distinct but complementary planes of representation for the behaviour of systems is introduced very early on.
The duality of the mechanical and the thermal appears again when systems are represented on two levels-that of the system as a whole and that of its particles. Each level has its own language and, again, they should be treated as complementary-which is the approach used in this topic book.
The complementary character of the mechanical and the thermal representations, or descriptions, requires the notion of energy. By adopting the broad definition of energy as that which can produce changes in the system which it enters, it proves possible to speak both of the differences between heat and work and also of their quantitative equivalence. The key is in the concept of internal energy, a concept that is poorly treated in most textbooks for sixth forms. In this topic book, internal energy is treated in a total way to include chemical, potential and thermal forms of energy.
The problems of measurement are not neglected. In particular, the problem of temperature measurement is used to emphasize the complexity of the decisions and lines of action that have to be taken if abstract definitions and experimental procedures are to coalesce. From the results of recent examinations, it would seem that the concept of temperatures is usually poorly understood by most sixth formers. In this topic book, it is treated in terms of the absolute thermodynamic scale, and the link between empirical scales of temperature and the Kelvin scale is discussed in some detail. Only in this way can temperature make sense.
The significance of thermal behaviour lies in the tendency of systems towards conditions of equilibrium-which correspond to states of maximum entropy. Entropy turns out to be a key concept in both chemistry and biology. It enters into explanations of chemical reactions, including changes of phase, and also into the study of the energetics of living systems. Within limits, the sooner a student is introduced to the concept of entropy, the better for his understanding of thermal physics. A lot of the difficulty students experience at university over this concept is caused simply by its unfamiliarity. The real problem in teaching it at the sixth form level lies in the fact that it means a deeper study of the concepts of energy and temperature-and in the sixth form, students all too often take it for granted that these are already understood.
However, there is an intrinsic difficulty in understanding entropy and it is still the subject of controversy, more than a hundred years after the term was coined (according to bad knowledge of Greek) by Clausius. But the importance of the concept of entropy far outweighs its difficulties. It is an example of a truly universal concept which can find an application in every domain ofhuman experience. It may well prove to be one of the pivotal notions in the network that will evolve to serve interdisciplinary studies.
This topic book may be considered as composed of two parts. In the first, there is a discussion of the concepts of internal energy, temperature and entropy. In the second, three quite distinctive kinds of thermodynamic systems are studied. As far as possible, the Study Units have been made independent of each other so that they can be used in whatever combination is desired, and at the times when they will be most useful. The first Study Unit provides its own key to those later Study Units in which certain problems can be studied. In the last four Study Units, it is assumed that material corresponding to the first four has already been assimilated. Strong linkages between Study Units are shown by the lines in the following concept map.