Thermophysics, the experiment 1

Monday 18. August, 2008

Today I had a measurement to do in our university’s physics student laboratory. I had a kettle full of water of 80 degrees Celsius, an aluminium rod and a smaller pot of room temperature water.

The idea was to conduct heat from the bottom of the hot kettle through the rod to the pot. I had temperature sensor in both the upper and the lower end of the rod and in the little pot. The temperatures were read to a computer running some Matlab-script. I was supposed to measure the temperatures for 10 minutes with 1 minute intervals and write them down (It cleary would have been too little work for us if the script had had a for-loop to do this too).

So, for ten minutes I wrote the results down and changed in a copper rod and did the same things to it too. In half way of the second measurement set, my instructor took a look on the first results and was a bit puzzled.

Somehow the upper end of the rod heated as expected, the water in the pot heated as well. But the temperature of the lower end of the rod got lower! How is this possible?

(this is an “I want comments”-post and the real answer to the question above will be revealed later, unless someone finds it out. >:-) )


One Response to “Thermophysics, the experiment 1”

  1. GODJonez Says:

    The aluminium rod you used surely wasn’t very thin, and with very thin I mean it’s just a line of atoms, so its crosscut diameter would only have been about 120 pm. So assuming it was thicker than that, there is a possibility of thermal conductivity wave interference.

    You should already know about thermal conductivity that if one point is in higher temperature than its surroundings, heat will move from the warmer point to the colder point. Of course, since your rod likely had a flat surface to get the heat from the boiling kettle, all the points in that surface were on equal temperature and as such the thermal conductivity should be linear the same way light goes linearly as per the Huygens–Fresnel principle.

    However, since this was an experiment, not a theoretical isolated system, external variables may have an effect on the system. Specifically the materials which keep the thermo-sensors used in place might have caused heat movement that caused such wave interference that actually made the result be lower temperature in the point where the lower sensor was.

    As the overall temperature of the rod increased during the experiment, also this wave interference phenomenon strengthened, causing the measured temperature drop even more in that point.

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