Thermal Conductivity


Concepts Shown:

General properties


4 rods of uniform size and shape made of glass, brass, aluminum, and stainless steel (approx. 1 foot long). 1 tin can (about 4-6") in diameter (look for size around the grocery store). Styrofoam container (to put can in ) or wrap.


Punch or drill a large hole in the center of the can to drain whatever is inside the can. Drill 4 holes in a square pattern equidistant from the center. The holes should be approximately the diameter of the rods, and filed to be smooth. Make a top out of hard styrofoam with the 4 holes matched up. A good way to do this is place small nails on top of the tin can holes and place the styrofoam on top to make markers. Punch these holes out and fit the rods into the top. Duct tape can be used to tighten the fit of the rods. Wrap the outside of the can with the styrofoam, or place it inside of the container. Presentation: Use a hot plate to boil some water just before the experiment. Pour the water into the can and place the top on, and let it sit for a few minutes. Then either pass the can around the room or have the students come up and feel it. They will notice that the steel and glass rods are not warm, yet the aluminum and brass are hot. You can compliment this with graphs of electrical conductivity, or by placing a piece of the particular material in a circuit (use a 6 volt battery), a light bulb and place a rod in series. The intensity of the light bulb will show the conductivity.)


Thermal conductivity, the ability to transfer energy as heat, is carried by the electrons in the material. In this case the electrons are excited by the hot water, and caries the heat up the rods. Noticeably the aluminum and brass carry the heat the best, with their thermal conductivity (k) being .22. and .12 W/mm C respectively. this is in sharp contrast to the Stainless Steel and glass which are .015 and .001 respectively. In correlation, due to similar mechanisms of travel, the electrical conductivity of each the materials is of the same order, with glass being the least conductive and aluminum being the most. Part B: This experiment also has a counterpart, you can use liquid nitrogen, instead of boiling water. The best way is to modify a dewar by making the 4 small holes in the top of the styrofoam lid. As a precaution place a piece of styrofoam on the bottom of the dewar so that the glass inside does not break and cause the dewar to implode. Use the same procedure for demonstration. Once again, be careful, secure the lid tightly.



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