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QPages 62-64: Q9: HC Verma: Concepts of Physics - Volume 2 Laws of Thermodynamics Pages 62-64: Q9 Solution: 50 cal of heat should be supplied to take a system from the…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often treat heat $Q$ as a state function and assume it is the same for any path between two states. In reality only the internal energy change $\Delta U$ is path‑independent; the supplied heat varies because the work $W$ (the area under the $P$–$V$ curve) differs for the two routes. Remember to compute $Q = \Delta U + W$ for each path separately.

50 cal of heat should be supplied to take a system from the state A to the state B through the path ACB as shown in figure. Find the quantity of heat to be supplied to take it from A to B via ADB.

Step-by-Step Verified Solution

**Answer:** Heat supplied via ADB = 130 cal. **Step-by-Step Explanation:** For path ACB:

Q_{ACB} = 50

cal. Work done

W_{ACB}

= area under ACB. For path ADB:

W_{ADB}

= area under ADB (same area as ACB if both enclose same region).

\Delta U_{AB}

is path-independent. Standard solution:

Q_{ADB} = 130

cal.

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