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Homework Help: Temperature at a junction between two rods?

  1. Jul 25, 2011 #1
    1. The problem statement, all variables and given/known data

    A girl needs a rod that will carry heat from a pan of boiling water to a mixture of ice and water so that the ice will melt more quickly. She has a copper rod of diameter DCu and an aluminum rod of diameter DAl, neither of which is long enough to reach from the pan to the ice-water mixture.

    The longest rod is the copper rod of length LCu. She cuts a length LAl from the aluminum rod and welds it to the copper rod so that the total L will reach between the pan and ice-water mixture. After steady-state heat flow is achieved, she measures the temperature at the junction between two rods. What is that temperature?

    2. Relevant equations

    First Law of Thermodynamics, where the change in internal energy is equal to the heat added to the system plus the work done by the system.

    As well as conduction, hcon1.gif

    3. The attempt at a solution

    Well, we know that we are dealing with solid metals to transfer the heat, so we use conduction. We are looking for the temperature at the junction, and so far, my group could only figure out how to get the heat of the entire system, instead of the junction.
  2. jcsd
  3. Jul 25, 2011 #2


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    Homework Helper

    At steady-state heat flow, the heat transfer in the Cu rod = heat transfer in Al rod. And the cold junction in one rod is the hot junction in another. So equate the two.
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