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A metal rod has one end held in boiling water and the other end held in melting ice. Which statement is correct?

1. All parts of the rod are in thermal equilibrium with each other
2. We can assign a single temperature to the rod
3. We can assign a single temperature to the rod only after steady state is reached
4. Once steady state is reached, the thermal state of the rod no longer changes

Correct answer: Once steady state is reached, the thermal state of the rod no longer changes

Solution

Because the two ends are at different temperatures there is a steady gradient; no single temperature can be assigned, but in steady state the temperature profile stops changing with time.

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