Reversible Cycles — Necessary Conditions for Reversibility Which condition(s) must be satisfied for a thermodynamic cycle to be reversible in practice and principle?

Introduction / Context:
Reversibility is an idealization central to defining the upper limit of efficiency. Real cycles can only approach, never reach, perfect reversibility. Understanding the conditions that must hold clarifies why all real devices generate entropy and fall short of reversible bounds.

Given Data / Assumptions:

• No heat transfer across finite temperature differences.
• No friction or viscous dissipation in any moving part or fluid flow.
• Quasi-static (infinitesimal gradients) evolution at every stage.

Concept / Approach:
Reversible processes require an infinite sequence of equilibrium states (quasi-static) and the absence of irreversibilities: mechanical (friction), thermal (finite temperature gradients), and non-equilibrium mixing or throttling. Consequently, slow operation, near-equality with surroundings, and frictionless components are all necessary conditions in the ideal model.

Step-by-Step Solution:
Assess option A: small or negligible driving forces ensure near-equilibrium heat/work exchange.Assess option B: extremely slow change is the practical route to maintain quasi-equilibrium.Assess option C: frictionless components prevent mechanical irreversibilities.Collectively, all must hold; therefore “all of the above” is correct.

Verification / Alternative check:
Any finite difference in temperature or pressure creates entropy generation. Likewise, friction converts mechanical work into internal energy, making the reverse path non-recoverable, violating reversibility.

Why Other Options Are Wrong:
Selecting only one or two conditions ignores other irreversible effects that still preclude reversibility; all are necessary in the idealization.

Common Pitfalls:
Thinking reversibility is achieved merely by slow operation; without eliminating friction and temperature differences, slow alone is insufficient.

Final Answer:
all of the above