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Several graphs show the temperature along an x-axis running straight through a wall made of three layers with different, nonzero, finite thermal conductivities, with different but uniform air temperatures on the two sides. Which of the depicted temperature profiles is/are impossible? (Mark the impossible case.)

1. (A)
2. (B)
3. (C)
4. (D)

Correct answer: (D)

Solution

A physically impossible profile is one violating steady-state heat conservation (e.g., a non-monotonic interior or a slope sign change without a source); option D depicts such a case.

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