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qz3sp09sol - PHY2054 Discussion-Spring 09 Quiz 3(Chapter...

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February 10, 2009 PHY2054 Discussion-Spring ‘09 Quiz 3 (Chapter 17.1-17.8) Name: UFID: *1. (2.5pts) In the Bohr model of the hydrogen atom, an electron ( e = 1.60×10 -19 C) moves around a proton in a circular path. What is the effective current associated with the electron motion if the electron moves with a speed of 1.50×10 6 m/s with a radius of 6.0×10 -11 m? The definition of current is the amount of charge that passes through a surface in one second. Thus the effective current is the number of revolution per second times electronic charge. We have I = ef = ev/(2πr) = 1.6×10 -19 ×1.5×10 6 /(2×3.14×6.0×10 -11 ) = 6.37×10 -4 A **2. (2.5pts) A 100-m long aluminum wire 5.00 mm in diameter carries a steady current of 5.00 A. Assuming one aluminum atom provides one electron, find how many days it takes one electron to travel the full length of the wire? The density of aluminum is 2.70 g/cm 3 and the atomic weight (or molar weight) is 27.0 (g/mol). According to our assumption, the number density of electron is the same as that of aluminum atoms, which is given by
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