A Study on the Heat Conduction in the Metal Rods -For the Re-examination of the Topic in the Elementary School Science-

Abstract

In order to examine the materials of the heat conduction in a metal rods which have been taught in the elementary school science, the author investigated the variables that affect to the heat conduction. When one end of a metal rod was heated and the heat conducted stationary, the temperature difference between the surface and the surroundings of the rod descended exponentially as the distance from the heat source become further. These results completely agree with the the theoretical expectation. It was also found that, the ratios of descendings of the temperature differences were affected by such variables as the cross section, the circle, the heat conductivity, the heat transfer coeffient from the surface of a rod. From the Newton's low of cooling, it was concluded that the heat transfer coefficient from the surface of a rod did not depend on the rod's shape, size, and the kind of the metal but only on the surface condition of the rod. In an experiment of the heat conduction written in the science textbooks, there metal rods (Cu, Al, Fe) of the same diameter are usually adopted. Although the comparative magnitudes of the temperasure conductivity of the metals are Cu>AI>Fe, as expected from the calculation, the experimental results are Cu≒AI>Fe. These phenomena due to the difference of the surface conditions of the rods. In this experiment one should keep the conditions of the rod's surfaces as same as possible by covering the surfaces with the metalic paint or by using the metal rods which have nearly the same surface condition. An experiment of the heat conduction in which one side end or a metal rod is heated and the other side end is put into water in a beaker, show very well that the ascendings of the water temperature are propotional to the heat conductivities of the rods. In any way one should recognize the distinction between the heat conductivity, and the temperature conductivity when he plans an experiment to show how the heat conducts in a metal rod.