ABSTRACT
At the beginning of the nineteenth century, when steam engines were relatively new, there was enormous interest in how their efficiency could be increased. An intellectual giant in this field was the French engineer Sadi Carnot, who in 1824 published an influential paper on how work could be produced from sources of heat. The second law of thermodynamics imposes limits on the efficiency of processes that convert heat into work, such as in a steam engine or internal combustion engine. It also leads to the concept of entropy, which is related both to bulk processes and to the microscopic arrangements within a system. The Clausius statement of the second law leads directly to a theorem that relates the Carnot cycle to other heat-engine cycles. The most efficient engine operating between a given pair of reservoirs is a Carnot engine. All Carnot engines operating between the same reservoirs have the same efficiency, independent of the nature of the working substance.
