The first law of thermodynamics can be written as ΔU = ΔQ + ΔW for an ideal gas. Which of the following statements is correct?
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Question

The first law of thermodynamics can be written as ΔU = ΔQ + ΔW for an ideal gas. Which of the following statements is correct?

G1 Physics · Accepted Answer

Use the first law Q=ΔU+W (W by the gas), ΔU=nCᵥΔT for an ideal gas, and the appropriate process relation. For Carnot devices, let T₁ be the cold-reservoir temperature and T₂ be the hot-reservoir temperature; η=1−T₁/T₂ and COP=T₁/(T₂−T₁). Evaluating the given data/statements gives C: ΔU is zero when heat is supplied and the temperature stays constant. Therefore the correct answer is C.