Physics 312 Lecture: "The Carnot Cycle and Second Law of Thermodynamics" May 11, 1998

• another way to state the Second Law of Thermodynamics is

  "heat does not spontaneously flow from cold to hot objects."

• a reversible process is one which can be performed in reverse so that the system is restored to its original condition
• it is NOT possible to reverse processes with friction or turbulence
• Carnot's Theorem state

  "no heat engine operating between two heat reservoirs can be more efficient than a reversible one."

• a corollary to Carnot's Theorem is that

  "all reversible engines operating between the same heat reservoirs have the same efficiency."

• one example of a reversible set of operations is the Carnot cycle, which goes
  • isothermal expansion (add heat)
  • adiabatic expansion
  • isothermal contraction (eject waste heat)
  • adiabatic contraction
• the efficiency of the Carnot cycle (or any reversible cycle) depends only on the temperatures of the hot and cold reservoirs:

                e = 1 - Tc/Th
  

• the Third Law of Thermodynamics states that

  "it is impossible to lower the temperature of any substance to zero Kelvin in a finite number of steps;"

  this makes it impossible to reach 100 percent efficiency

This lecture discusses material in Chapter 22 of Serway.

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