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Question:

An ideal gas goes from state A to state B via three different processes as indicated in the P-V diagram. If Q1, Q2, Q3 indicate the heat absorbed by the gas along the three processes and ΔU1, ΔU2, ΔU3 indicate the change in internal energy along the three processes respectively, then which of the following is correct?

Q3>Q2>Q1 and ΔU1=ΔU2=ΔU3

Q3>Q2>Q1 and ΔU1>ΔU2>ΔU3

Q1>Q2>Q3 and ΔU1=ΔU2=ΔU3

Q1=Q2=Q3 and ΔU1>ΔU2>ΔU3

Solution:

ΔU1=ΔU2=ΔU3
Q1>Q2>Q3
Because ΔQ=ΔW+ΔU
Change in internal energy is independent of path and work depends on path and the heat required increases as the work done increases.
∴ ΔQ1>ΔQ2>ΔQ3