The laws of thermodynamics underpin everything from the connection between your weight, your calorie intake and your exercise levels to fundamental questions such as whether time has a natural direction. As Einstein put it, "Classical thermodynamics .... is the only physical theory of universal content which I am convinced will never be overthrown." Indeed, modern developments have served to reinforce rather than to replace the laws of thermodynamics. In particular, the development of a statistical approach has often allowed classical results for the macroscopic properties of a system to be understood from the microscopic properties, averaged over very large numbers of constituents. Running ever-present through both the classical and the statistical approaches is the enigmatic concept of entropy, the understanding of which is a central aim of this module. The module first covers the laws of thermodynamics and explores their practical consequences, for example in the design of engines and refrigerators and in the quest for ultra-low temperatures.
After some revision of the basic theory of probability and statistics, the module moves on to explain the basis of heat transfer and thermal equilibrium from a statistical standpoint. The macroscopic properties of physical systems as varied as paramagnetic solids and diatomic gases are then derived using statistical techniques, under conditions of both thermal isolation and fixed temperature.