770_Physics ProblemsTechnical Physics

770_Physics ProblemsTechnical Physics - 110 P27.11 Current...

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110 Current and Resistance P27.11 We use In q A v d = n is the number of charge carriers per unit volume, and is identical to the number of atoms per unit volume. We assume a contribution of 1 free electron per atom in the relationship above. For aluminum, which has a molar mass of 27, we know that Avogadro’s number of atoms, N A , has a mass of 27.0 g. Thus, the mass per atom is 27 0 27 0 602 10 449 10 23 23 .. . . g g ga tom N A = × . Thus, n == × density of aluminum mass per atom gcm 3 270 23 . . n 6 02 10 6 02 10 22 28 atoms cm atoms m 33 . Therefore, v I nqA d ×× × −− 500 6 02 10 1 60 10 4 00 10 130 10 28 3 19 6 4 . . . A m C m ms 2 ej e j e j or, v d = 0130 . m m s . Section 27.2 Resistance *P27.12 JE E = ×⋅ F H G I K J σ ρ 0740 244 10 1 303 10 8 7 . . . Vm m A 1 V Am 2 P27.13 I V R = = 120 0500 V 240 A m A . P27.14 (a) Applying its definition, we find the resistance of the rod,
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