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Unformatted text preview: LAB# 19 COEFFICIENT OF LINEAR EXPANSION Introduction: The objective of this experiment is to measure the coefficient of linear expansion of copper, steel and aluminum by directly measuring the expansion in a length of tube (made of copper, steel or aluminum) as the temperature of the tube is increased from room temperature. Figure 1: Equipment for the Coefficient of Linear Expansion experiment showing the expansion tube apparatus, metal tubs, steam generator, multimeter and condensation collection container. Equipment: Expansion tube apparatus and steam generator, elevation block, Digital ohmmeter, rods of Steel, Cu and Al metal. A container to collect the condensed steam. Theory: Most materials expand somewhat when heated through a temperature range that does not produce a change in phase (that is changing from a solid to a liquid or from a liquid to a gas). The added heat increases the average amplitude of vibration of the atoms in the material which increases the average separation between the atoms. Suppose an object of length L undergoes a temperature change of magnitude T . If T is reasonably small, the change in length, L , is generally proportional to L and T . Stated mathematically: , . T L L (1) where is called the coefficient of linear expansion for the material. This, of course, assumes that the material will have the same expansion in all directions for a given temperature change. This is true for each of the materials we will be using, but not true for all materials (materials that exhibit this type of behavior, same expansion in all directions, are called isotropic ). Typically will also vary somewhat with temperature so that the degree of expansion depends not only on the magnitude of the temperature change, but on the absolute temperature as well. That is, in which temperature range is the expansion taking place. In this experiment, you will measure...
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- Fall '08