Carnot efficiency

Definition

Carnot efficiency is the maximum possible efficiency that a heat engine can achieve, operating between two thermal reservoirs. It is determined solely by the temperatures of the hot and cold reservoirs.

5 Must Know Facts For Your Next Test

1. Carnot efficiency is given by the formula: $\eta = 1 - \frac{T_C}{T_H}$, where $T_C$ is the absolute temperature of the cold reservoir and $T_H$ is the absolute temperature of the hot reservoir.
2. No real engine can be more efficient than a Carnot engine operating between the same two reservoirs.
3. The Carnot cycle consists of two isothermal processes and two adiabatic processes.
4. The efficiency depends only on the temperatures of the reservoirs and not on any specific details of the working substance or process.
5. Increasing the temperature difference between $T_H$ and $T_C$ increases Carnot efficiency.

Review Questions

• What is the formula for calculating Carnot efficiency?
• Why can't any real engine exceed Carnot efficiency?
• How does increasing the temperature difference between $T_H$ and $T_C$ affect Carnot efficiency?

Related terms

Second Law of Thermodynamics: States that heat cannot spontaneously flow from a colder body to a hotter body and that no engine can be perfectly efficient.

Heat Engine: A device that converts thermal energy into mechanical work.

Thermal Reservoir: A large body with a constant temperature that can supply or absorb finite amounts of heat without undergoing any change in temperature.