MSE 2620, Spring ‘09
Homework #2
Instructions:
Due
Tuesday, February 26
th
, 2009.
Turn in one solution per group and be sure to include
the group letter, the names of the group members, and if any group members did not participate
enough to deserve full credit along with the reasons why.
Question 1: Conductivity and The Mean Free Path
a)
Sodium is a monovalent metal with a density of 0.97g/cm
3
and a BCC crystal structure.
Estimate the mean separation (nm) between an electron and one metal ion, assuming that
electrons spend the most time between a metal ion and its second nearest neighbor.
b)
Use the potential energy between this electron and metal ion pair to find the mean speed
of an electron (m/s) (HINT: Virial Theorem).
c)
Given that the mean free time between scattering events from thermal vibrations of the
lattice is 4.3E14s, find the drift mobility (m
2
/Vs), the conductivity
(1/Ωm)
and the mean free
path of an electron (m).
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 Spring '09
 MALLIARAS
 1m, 2mm, 3 k, 0.05mm, 0.97g

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