Linear Thermal Expansion

The term thermal expansion refers to the increase in size of an object as that object is heated. With relatively few exceptions, all objects expand when they are heated and contract when they are cooled. Perhaps the most important exception to this rule is water. Water contracts as it cools from its boiling point to about 39. 2°F (4°C). At that point, it begins to expand as it cools further to its freezing point.
This unusual effect explains the fact that ice is less dense than water.Different materials expand or contract at different rates. In general, gases expand more than liquids, and liquids expand more than solids. When an object is heated or cooled, it expands or contracts in all dimensions. However, for practical reasons, scientists and engineers often focus on two different kinds of expansion, or expansivity: linear expansivity (expansion in one direction only) and volume expansivity (expansion in all three dimensions). The amount by which any given material Joints such as this one are used in bridges to accommodate thermal expansion.Objective To determinate the average coefficient of linear Expansion of the copper rod.
Theory: Solids Expand as they are heated and contract if they are cooled. Thus their length is function of temperature. Thus , when the temperature of an object is increased by ? T, its Length L initial increases by ? L. Apparatus: – Dial Gauge – Thermometer – Cu rod – Rubber tube – Boiler – Hot plate Method * Measure the initial length of Copper rod, with a meter stick at room temperature. * Adjust the micrometer dial at zero. Insert the thermometer in the top of the copper rod and record its reading at room temperature. * Start heating the water by switching in the electric hot plate to maximum and wait until the steam is generated from the water boiler.
When the rod reaches a constant uniform temperature, measure the corresponding change in the length ? l. * Switch off the hot plate and immediately record ? l (on the dial micrometer) and the temperature measure T ( on the thermometer ) upon cooling.

Prof. Angela


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