Verified Solution • 2025–26 Session moderate

QPage 60: Q1: Laws of Thermodynamics Solutions — HC Verma: Concepts of Physics - Volume 2

⚠️ Common Exam Traps & Conceptual Pitfalls

Many students equate added heat directly with an increase in internal energy, ignoring the work term in the first law, $Delta Q=Delta U+Delta W$. Remember that if the system does work (e.g., in an isothermal expansion where $Delta T=0$), the heat supplied can be entirely converted into work, leaving $Delta U=0$.

Should the internal energy of a system necessarily increase if heat is added to it?

Step-by-Step Verified Solution

**Answer:** No, the internal energy of a system does not necessarily increase if heat is added to it. **Step-by-Step Explanation:** According to the first law of thermodynamics, ΔQ=ΔU+ΔW\Delta Q = \Delta U + \Delta W. If heat ΔQ\Delta Q is added to a system, it may be entirely converted into work ΔW\Delta W with no change in internal energy, as happens in an **isothermal process**. In an isothermal process, ΔT=0\Delta T = 0, so ΔU=0\Delta U = 0, and all the heat supplied is used to do work [citation:8][citation:10].

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