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#Kelvin-Planck

2 public questions tagged with this topic.

Cyclic Processes and Reversibility Concepts

Which of the following statements is correct regarding the Kelvin-Planck statement?

**Reversibility** reversible process can be reversed by infinitesimal change, no entropy production, quasi-static without friction, e.g., Carnot cycle reversible, irreversible processes involve friction, free expansion, heat transfer across finite temperature difference, entropy increases, most real processes irreversible. The Kelvin-Planck statement asserts that no engine can absorb heat from a single reservoir and convert it entirely to work, requiring heat rejection to a colder reservoir. Option D is correct. Using first law ΔU = Q - W, W = ∫ P dV, isobaric W = P ΔV, isothermal W = n R T ln(V₂/V₁), adiabatic P V^γ = const and η = 1 - T_c/T_h, evaluation

Ref: NCERT > Physics Book > Thermodynamics > Cyclic Processes and Reversibility Concepts

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Isobaric and Isothermal Processes Work Calculation

According to the Kelvin-Planck statement, what is impossible for a heat engine?

**Isobaric process** constant pressure, work W = P ΔV = P(V₂ - V₁) = n R ΔT, for expansion ΔV positive W positive, for compression negative, heat Q = n C_p ΔT, ΔU = n C_v ΔT. Isothermal process constant temperature ΔU=0, work W = n R T ln(V₂/V₁) = n R T ln(P₁/P₂), Q = W, heat absorbed equals work done. The Kelvin-Planck statement of the Second Law states that no process can absorb heat from a single reservoir and convert it entirely into work without rejecting some heat to a colder reservoir. This limits efficiency to less than 100%. Using first law ΔU

Ref: NCERT > Physics Book > Thermodynamics > Isobaric and Isothermal Processes Work Calculation

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