ism_chapter_38

ism_chapter_38 - Chapter 38 Solids and the Theory of...

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1261 Chapter 38 Solids and the Theory of Conduction Conceptual Problems 1 Determine the Concept The energy lost by the electrons in collision with the ions of the crystal lattice appears as Joule heat ( I 2 R ). *2 Determine the Concept The resistivity of brass at 4 K is almost entirely due to the residual resistance, the resistance due to impurities and other imperfections of the crystal lattice. In brass, the zinc ions act as impurities in copper. In pure copper, the resistivity at 4 K is due to its residual resistance, which is very low if the copper is very pure. 3 Picture the Problem The contact potential is given by e V 2 1 contact φ = , where 1 and 2 are the work functions of the two different metals in contact with each other. ( a ) Express the contact potential in terms of the work functions of the metals: e V 2 1 contact = joined. are nickel and potassium occur when will functions work e between th difference greatest that the see we 2, - 38 Table Examining ( b ) Substitute numerical values and evaluate V contact : () ( ) V 10 . 3 C 10 60 . 1 J/eV 10 60 . 1 eV 1 . 2 eV 2 . 5 19 19 contact = × × = V 4 Picture the Problem The contact potential is given by e V 2 1 contact = , where 1 and 2 are the work functions of the two different metals in contact with each other. ( a ) Express the contact potential in terms of the work functions of the metals: e V 2 1 contact =
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Chapter 38 1262 joined. are gold and silver occur when will functions work e between th difference least that the see we 2, - 38 Table Examining ( b ) Substitute numerical values and evaluate V contact : () ( ) V 100 . 0 C 10 60 . 1 J/eV 10 60 . 1 eV 7 . 4 eV 8 . 4 19 19 contact = × × = V 5 Determine the Concept If the valence band is only partially full, there are many available empty energy states in the band, and the electrons in the band can easily be raised to a higher energy state by an electric field. ( ) correct. is c 6 Determine the Concept Insulators are poor conductors of electricity because there is a large energy gap between the full valence band and the next higher band where electrons can exist. correct. is b 7 ( a ) True ( b ) False. The classical free-electron theory predicts heat capacities for metals that are not observed experimentally. ( c ) True ( d ) False. The Fermi energy is the energy of the last filled (or half-filled) level at T = 0. ( e ) True ( f ) True ( g ) False. Because semiconductors conduct current by electrons and holes, their conduction is in both directions. *8 Determine the Concept The resistivity of copper increases with increasing temperature; the resistivity of (pure) silicon decreases with increasing temperature because the number of charge carriers increases. 9 Determine the Concept Because a gallium atom can accept electrons from the valence band of germanium to complete its four covalent bonds, ( ) correct. is b
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Solids and the Theory of Conduction 1263 10 Determine the Concept Because phosphorus has 3 electrons that it can donate to the conduction band of germanium without leaving holes in the valence band, () correct. is d 11
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ism_chapter_38 - Chapter 38 Solids and the Theory of...

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