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?

70 degC
50 degC
30 degC
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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