ABSTRACT
The second law of thermodynamics imposes limits on the efficiency of processes which convert heat into work, such as steam or internal combustion engines. It will allow us to set up the thermodynamic temperature scale which is independent of the nature of the thermometric substance, and to define the concept of entropy, which we shall see is related to the microscopic disorder in the system. At the beginning of the nineteenth century, when steam engines were in their infancy, there was enormous interest in how their efficiency could be increased. The Carnot engine is an idealized engine. Real engines operate in various cycles, all different from the idealized Carnot one.
