46 a photograph of power transmission lines showing

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Unformatted text preview: rs” between the transmission lines and the towers are usually made from ionic solids. Explain the choice of materials for these three applications. Solution To minimize the power loss associated with the resistance of the transmission lines, it is necessary to select a material with a high electrical conductivity. Thus, metals rather than ionic compounds are used for this application. The structural support material is selected for its mechanical rather than its electrical properties. It would be unwise to fabricate these towers from a brittle material, since the structure may experience high loads from many sources including gusts of wind and FIGURE 2.4–6 A photograph of power transmission lines showing the metal support structure, the ceramic insulators, and the wires carrying the electric current. (Source: Courtesy of Commonwealth Edison.) | v v 38 pgm 1-22-98 plm 3-21-98 MP | e-Text Main Menu | Textbook Table of Contents pg039 [R] G1 7-27060 / IRWIN / Schaffer pgm 1-19-98 plm 3-21-98 MP rps 01-20-98 MP Chapter 2 Atomic Scale Structures 39 pg794 [V] G14 7-27060 / IRWIN / Schaffer possible collisions with motor vehicles. In addition, because of their high ductility, metals are more easily formed into large and complex shapes. Finally, we must consider the purpose of the 805 Glossary “spacers.” If the metal transmission lines are in close proximity to the metal support structure, the possibility of a short circuit that will electrify the entire structure exists. Therefore, the wires must be insulated from the support structure by using a high–electrical-resistance ionic solid as the “spacer.” volumetric density The number of atoms centered in a distributed v v uniformly 794 Glossary ....................................................................................................................................... unit volume of crystal. Often the volume considered is the strain is also uniform. the unit cell. entation of a material. In bond anglesthermal expansion coefficient...
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