UNIVERSITY OF MASSACHUSETTS DARTMOUTH
COLLEGE OF ENGINEERING
EGR 101 INTRODUCTION TO ENGINEERING I
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This assignment is due Tuesday, October 2, 2012.
Use engineering papers.
Show all of your steps.
Present your work neatly and clearly.
Box your final answers.
# 2; # 5 and # 14 on page 41 of your textbook.
Problem 1
Consider e-t/RC, where R is resistance in Ohms, C is capacitance in Farads, and t is time in s
a) what are the units associated with the product R*C
b) Look up the definition of Farad. Determine how you could get the units from part a) from
R*C. Hint: you may have to use Ohm's law to find a suitable form for the resistance.
c) If R = 1 MΩ and C = 1 µf , use excel to plot e-t/RC , for the interval 0 ≤ t ≤ 10 sec
Problem 2
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Find the % increase or decrease in resistance of a wire whose diameter is halved
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Find the ratio of the resistance of copper to that of aluminum for two wires of the same
length and diameter.
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Find the diameter of a copper wire that has the same length and resistance of an
aluminum wire. The aluminum wire has a diameter of 0.1 mm.
Problem 3
A battery provides 16,000 J of energy by virtue of the internal chemical reaction, which is
capable of moving 5 x 1020 e- through a wire.
 What is the charge Q in Coulomb (C)?
 What is the voltage of the battery in Volts (V)?
 What is the current in (μA) if the charges take 3 months to pass through a section of the
wire?