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QPage 60: Q5: HC Verma: Concepts of Physics - Volume 2 Laws of Thermodynamics Page 60: Q5 Solution: The outer surface of a cylinder containing a gas is rubbed…

⚠️ Common Exam Traps & Conceptual Pitfalls

When a cylinder is rubbed, the frictional force acts on the wall, not on the gas; since the gas volume remains constant, $W=P,Delta V=0$. The energy transferred is heat $Q$, not work.

The outer surface of a cylinder containing a gas is rubbed vigorously by a polishing machine. The cylinder and its gas become warm. Is the energy transferred to the gas heat or work?

Step-by-Step Verified Solution

**Answer:** The energy transferred to the gas is **heat**. **Step-by-Step Explanation:** Rubbing the outer surface does not change the volume of the gas, so no work is done on the gas. The friction between the polishing machine and the cylinder generates heat, which is transferred to the gas through the cylinder walls. Thus, the energy transfer is **heat** [citation:8][citation:10].

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