Which of the following statements correctly describes the First Law of Thermodynamics?
**Isobaric and isothermal** are fundamental thermodynamic processes, isobaric P constant horizontal line on P-V diagram, isothermal hyperbolic P = n R T/V, work equals area under curve, isothermal work larger than adiabatic for same volume change because pressure higher. The First Law ( Δ Q = Δ U + Δ W ) is a conservation principle, stating heat added equals internal energy increase plus work done. 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 -
Ref: NCERT > Physics Book > Thermodynamics > Isobaric and Isothermal Processes Work Calculation