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1216_Physics ProblemsTechnical Physics

1216_Physics ProblemsTechnical Physics - Chapter 43 P43.29...

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Chapter 43 557 P43.29 For sodium, M = 23 0 . g mol and ρ = 0 971 . g cm 3 . (a) n N M e = = × A 3 electrons mol g cm g mol ρ 6 02 10 0 971 23 0 23 . . . e je j n e = × = × 2 54 10 2 54 10 22 28 . . electrons cm electrons m 3 3 (b) E h m n e F J s kg m J eV = F H G I K J F H G I K J = × × × L N M M O Q P P = × = 2 2 3 34 2 31 28 3 2 3 19 2 3 8 6 626 10 2 9 11 10 3 2 54 10 8 5 05 10 3 15 π π . . . . . e j e j e j P43.30 The melting point of silver is 1 234 K. Its Fermi energy at 300 K is 5.48 eV. The approximate fraction of electrons excited is k T E B F J K K eV J eV = × × 1 38 10 1 234 5 48 1 60 10 2% 23 19 . . . e j b g a f e j . P43.31 Taking E F eV = 5 48 . for sodium at 800 K, f e e E E k T E E k T E E k T B B B = + = = = = = − F F F b g b g b g 1 0 950 1 0 950 1 0 052 6 0 052 6 2 94 1 . . . ln . . E E = − × × = − F J 1.60 10 J eV eV 2 94 1 38 10 800 0 203 23 19 . . . e j a f or E = 5 28 . eV . P43.32 d = 1 00 . mm, so V = × = × 1 00 10 1 00 10
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