The efficiency of an ideal reversible heat engine, also known as the Carnot engine, is determined by the temperatures of the heat source and the heat sink between which it operates. The efficiency of such an engine is given by the Carnot efficiency formula:
Efficiency = 1 - (Tc/Th)
where Tc is the temperature of the cold reservoir (heat sink) and Th is the temperature of the hot reservoir (heat source). The temperatures must be in absolute units, such as Kelvin.
The Carnot efficiency represents the maximum possible efficiency that any heat engine operating between two temperatures can achieve. It is based on the principles of thermodynamics and assumes that the engine is operating reversibly, without any internal losses or irreversibilities.
Therefore, the efficiency of an ideal reversible heat engine is 100% or at its maximum when the temperature of the cold reservoir approaches absolute zero (0 K) or when the temperature difference between the hot and cold reservoirs is maximized. In practical terms, achieving absolute zero is not possible, so an ideal reversible heat engine cannot achieve 100% efficiency in real-world scenarios. However, the Carnot efficiency serves as a theoretical upper limit against which the performance of real heat engines can be compared.