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#laws of thermodynamics

3 public questions tagged with this topic.

Work Heat Distinction and Energy Transfer Modes

Which of the following statements is correct regarding the Zeroth Law of Thermodynamics?

**Modes of energy transfer** work is force times displacement, e.g., gas expansion W = P ΔV, heat is due to temperature gradient, internal energy change same for different combinations of Q and W, e.g., same ΔU can be achieved by adding heat at constant volume or doing work adiabatically, illustrating equivalence but distinction in mechanism. The Zeroth Law states that if two systems are in thermal equilibrium with a third, they are in equilibrium with each other, establishing temperature as a measurable property. It does not involve heat flow direction or work, which are addressed by other laws. Using first law ΔU = Q -

Ref: NCERT > Physics Book > Thermodynamics > Work Heat Distinction and Energy Transfer Modes

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First Law of Thermodynamics Applications

Which of the following statements is incorrect about the Zeroth Law of Thermodynamics?

**First law applications** for isobaric W = P ΔV, Q = n C_p ΔT, ΔU = n C_v ΔT, for isothermal ideal gas ΔU=0 Q=W=n R T ln(V₂/V₁), for adiabatic Q=0 W= -ΔU = (P₁V₁ - P₂V₂)/(γ-1), for isochoric W=0 ΔU=Q=n C_v ΔT, enabling calculation of Q,W,ΔU for any process. The Zeroth Law defines temperature through thermal equilibrium but does not address heat flow direction (Second Law) or energy conservation (First Law). Option C is incorrect. 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 > First Law of Thermodynamics Applications

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Adiabatic Processes and Gamma Determination

Which of the following statements is correct about the Second Law of Thermodynamics?

**Adiabatic process** no heat exchange Q=0, first law ΔU = -W, for ideal gas P V^γ = constant, T V^{γ-1}= constant, P^{1-γ} T^{γ}= constant, γ = C_p/C_v = (f+2)/f, monatomic γ=5/3, diatomic γ=7/5. Work done W = (P₁V₁ - P₂V₂)/(γ-1), temperature changes due to work. The Second Law (Clausius statement) states that heat cannot flow from a colder to a hotter body without work, reflecting natural directionality. 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 = const and η = 1

Ref: NCERT > Physics Book > Thermodynamics > Adiabatic Processes and Gamma Determination

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