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8/3/2019 FINAL EXAM Fall 2009 Practice
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ENGR 220
PRACTICE FINAL EXAMINATION
M. Marcolongo Fall,2009
Name____________________________ Section_____________
You have two hours to complete the final exam. Feel free to use
your calculator, periodic tableand ruler. You must show all work
for full credit.
1. (15%, 1% each) Please respond True or False to the statements
listed below. Kindly writeout complete word.
RECORD YOUR ANSWERS ON THE SPACES GIVEN AT THE BOTTOM OF
PAGES
ONE AND TWO.
(a) Fiberglass and window glass of the same composition have
different mechanicalproperties because they are processed
differently.
(b) Interatomic separation distance is at an equilibrium level
when the potential energy isequal to zero.
(c) For a face centered cubic crystal structure, the
relationship between lattice parameter, a,and atomic radius, R, is
a=4R/ (3)1/2.
(d)A solid solution can be formed when impurity atoms are added
to a host material.
(e) The delivery of insulin through an implanted hydrogel
polymer catheter is an example ofsteady state diffusion.
(f) An electron can exist as a particle and a
wave.(g)Cross-linking of polymers gives them higher resistance to
degradation by swelling.
Answers (True of False, write out complete word, please):
a. ___________b. ___________c. ___________d. ___________e.
___________f. ___________g. ___________
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8/3/2019 FINAL EXAM Fall 2009 Practice
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(h)Conductivity for metals increases with rising temperature.(i)
The oxidation reaction for Fe(+2) is Fe Fe(+2) + 2 electrons and
occurs at the anode.(j) Absorption of visible light can occur by
two mechanisms: electric polarization and
electron transitions.
(k)A hard magnet has a greater degree of hysteresis than a soft
magnet.(l) The melt temperature is the temperature where a material
shows a change in stiffness
from a brittle (glassy) modulus to a more compliant (rubbery)
modulus.
(m)If two metals are to be used adjacent to each other in an
underwater application, a wisematerials engineer would choose two
metals that are far apart on the Galvanic series to
limit the amount of corrosion.
(n)Resistance is a material property, while resistivity is a
design property.(o) Im ready to celebrate the holidays!
Answers to Problem 1, continued.
h. ___________i. ___________j. ___________k. ___________l.
___________m. ___________n. ___________o. ___________
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8/3/2019 FINAL EXAM Fall 2009 Practice
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2. (20%)(a) (5%) Why is snow white even though ice is
transparent?
(b) (15%) Zinc selenide has a band gap of 2.58 eV. Over what
range of wavelengths of visiblelight is it transparent?
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8/3/2019 FINAL EXAM Fall 2009 Practice
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3. (15%)(a) (10%) Briefly describe magnetic hysteresis and
explain why it occurs for
ferromagnetic materials.
(b) (5%) Cite differences between hard and soft magnetic
materials in terms of both
hysteresis behavior and typical applications.
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8/3/2019 FINAL EXAM Fall 2009 Practice
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Grades: #1__________ #2____________ #3____________
#4_________ #5___________ #6____________ Total____________
4. (25 pts)
(a) (10pts)Using band theory, explain why the conductivity of
metals is higher than semi-
conductors and why the conductivity of semi-conductors is higher
than ceramics.
(b) (15pts) At room temperature the electrical conductivity and
the electron mobility foraluminum are 3.8 x 107 (ohm-m)-1 and
0.0012 m2/V-s, respectively. Compute the number of free
electrons per cubic meter for aluminum at room temperature. What
is the number of free
electrons per aluminum atom? Assume a density of 2.7 g/cm3.
