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#extensive variables

2 public questions tagged with this topic.

Cyclic Processes and Reversibility Concepts

Which of the following statements is correct about extensive variables?

**Cyclic process** system returns to initial state, ΔU=0 over cycle, net work W_net = area enclosed in P-V diagram, Q_net = W_net from first law ΔU= Q - W =0 => Q_net = W_net, clockwise cycle work done by system positive, counterclockwise work done on system negative, efficiency η = W_net/Q_in. Extensive variables (e.g., volume, internal energy) scale with the system’s size, halving when the system is halved, unlike intensive variables (e.g., pressure). Option C 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

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

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Second Law Heat Engines and Kelvin-Planck

What property distinguishes intensive variables from extensive variables?

**Carnot engine** reversible engine operating between T_h and T_c has maximum efficiency η =1 - T_c/T_h, T in kelvin, e.g., T_h=400 K T_c=300 K η=0.25, real engines less due to irreversibilities, second law defines direction of spontaneous processes and entropy increase. Intensive variables (e.g., pressure, temperature) do not depend on the system’s size or amount, remaining unchanged when the system is divided. Extensive variables (e.g., volume, internal energy) scale with the system’s size. 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

Ref: NCERT > Physics Book > Thermodynamics > Second Law Heat Engines and Kelvin-Planck

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