Thermal Physics -- Change of energy from compression

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SUMMARY

The discussion centers on the concept of reversible processes in thermal physics, specifically regarding energy changes during compression. The participant questions how a system can remain in the same quantum state while its energy changes due to mechanical work applied during slow volume reduction. The example provided illustrates a particle in a one-dimensional box, where decreasing the box length results in a change in energy while maintaining the particle in its ground state. This highlights the distinction between quantum states and energy levels in reversible processes.

PREREQUISITES
  • Understanding of quantum mechanics, specifically quantum states and energy levels
  • Familiarity with the principles of thermodynamics, particularly reversible processes
  • Knowledge of mechanical work and its relation to energy changes in a system
  • Basic concepts of thermal reservoirs and their impact on system states
NEXT STEPS
  • Study the principles of reversible and irreversible processes in thermodynamics
  • Explore quantum mechanics focusing on energy quantization and state transitions
  • Investigate the role of thermal reservoirs in maintaining equilibrium during energy changes
  • Examine practical applications of these concepts in systems like engines or refrigeration cycles
USEFUL FOR

Students of physics, particularly those studying thermal physics and quantum mechanics, as well as educators seeking to clarify the concepts of energy changes and reversible processes.

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Homework Statement


This is not a homework problem but rather a passage from my textbook that I don't understand. I don't think I quite understand the concept of reversible processes. Here is the passage from my book:

"Consider a system in the quantum state s of energy Es. We assume Es to be a function of the volume of the system. The volume is decreased slowly by application of an external force. Let the volume change take place sufficiently slowly that the system remains in the same quantum state s throughout the compression...The mechanical work done on the system by the pressure in a contraction appears as the change of energy of the system."

My question is:
How is it possible that the system can remain in the same quantum state throughout the compression if the energy is changing? (I believe the system under consideration is in contact with a thermal reservoir)

Homework Equations

The Attempt at a Solution

 
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As an example, think of a particle in the ground state in a one dimensional box of length L. Imagine slowly decreasing L such that the particle is always in the ground state corresponding to the current value of L. Does the energy of the particle change?
 

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