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February 10, 2009
PHY2054 DiscussionSpring ‘09
Quiz 3 (Chapter 17.117.8)
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 100m 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,
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This note was uploaded on 12/13/2011 for the course PHY 2054 taught by Professor Avery during the Fall '08 term at University of Florida.
 Fall '08
 Avery
 Physics, Current

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