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QPage 11: Q7: HC Verma: Concepts of Physics - Volume 2 Heat and Temperature Page 11: Q7 Solution: The length of a brass rod is found to be less on a hot summer…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often confuse the measured length change with the actual physical change, ignoring that the measuring scale itself expands. Recognize that the reading is a relative quantity dependent on the difference in linear expansion coefficients ($\alpha_{\text{rod}} - \alpha_{\text{scale}}$), not the absolute expansion of the rod alone.

The length of a brass rod is found to be less on a hot summer day than on a cold winter day as measured by the same aluminium scale. Can we conclude that brass shrinks on heating?

Step-by-Step Verified Solution

**Answer:** No, we cannot conclude that brass shrinks on heating. **Step-by-Step Explanation:** The aluminium scale also expands on a hot day. If brass expands less than aluminium, the aluminium scale's markings spread farther apart, making the brass rod appear shorter. The observed shortening is a relative effect due to the difference in expansion coefficients. We can only conclude αbrass<αaluminium\alpha_{\text{brass}} < \alpha_{\text{aluminium}}.

All Questions in this Chapter

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