Coefficient of Linear Expansion
Coefficient of Linear Expansion
Introduction
With few exceptions materials expand somewhat when heated through a temperature range that does not produce a change in phase (i.e. melting, freezing, boiling etc.). The added heat increases the average amplitude of vibration of the atoms in the material, which increases the average separation between the atoms. Although this effect is small, it is very important in any application that involves using different materials in an environment where they are heated and cooled. For example, if a rivet of one metal is used inside a hole in a different material, it can become too tight or too loose if the thermal expansion of the materials is very different.
Theory
For solids that are isotropic (i.e. uniform in all directions), the material undergoes thermal expansion as a whole: that is its volume expands. For materials that are not isotropic such as an asymmetric crystal for example, the thermal expansion can have different values in different directions. Thermal expansion can 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.
Procedure
To make this measurement the metal rod is measured and placed in the apparatus. The reading on the built-in dial micrometer is recorded at room temperature, then, steam is passed around it. The expansion of the metal is measured using the dial micrometer. Fill the boiler about one-half full of water, cap it loosely, and connect the rubber hose to its spout. Heat with a Bunsen burner. First, measure the length, L, of the rod using a meter stick and make an estimate of the uncertainty in the length and call this number all. Next, insert the rod into the aluminium jacket and put it in place on the supporting apparatus. It is very important that the rod is properly placed. One end must be firmly pressed against the screw protruding from the supporting apparatus, while the
Introduction
With few exceptions materials expand somewhat when heated through a temperature range that does not produce a change in phase (i.e. melting, freezing, boiling etc.). The added heat increases the average amplitude of vibration of the atoms in the material, which increases the average separation between the atoms. Although this effect is small, it is very important in any application that involves using different materials in an environment where they are heated and cooled. For example, if a rivet of one metal is used inside a hole in a different material, it can become too tight or too loose if the thermal expansion of the materials is very different.
Theory
For solids that are isotropic (i.e. uniform in all directions), the material undergoes thermal expansion as a whole: that is its volume expands. For materials that are not isotropic such as an asymmetric crystal for example, the thermal expansion can have different values in different directions. Thermal expansion can 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.
Procedure
To make this measurement the metal rod is measured and placed in the apparatus. The reading on the built-in dial micrometer is recorded at room temperature, then, steam is passed around it. The expansion of the metal is measured using the dial micrometer. Fill the boiler about one-half full of water, cap it loosely, and connect the rubber hose to its spout. Heat with a Bunsen burner. First, measure the length, L, of the rod using a meter stick and make an estimate of the uncertainty in the length and call this number all. Next, insert the rod into the aluminium jacket and put it in place on the supporting apparatus. It is very important that the rod is properly placed. One end must be firmly pressed against the screw protruding from the supporting apparatus, while the