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Two rods of identical dimensions connect heat baths at 100 degC and 0 degC, and the steady-state junction temperature is 70 degC. If the two rods are swapped (interchanged), what is the new junction temperature?

1. 70 degC
2. 50 degC
3. 30 degC
4. can't determine

Correct answer: 30 degC

Solution

The junction at 70 degC gives conductivity ratio k1/k2 = 30/70; after interchanging, the temperature drops symmetrically and the new junction sits at 30 degC.

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