Download H.W. Solution for Lect. (1)

Lecture (1): Electrical Conductivity
Homework Solution
1) An aluminum wire 10 m long must experience a voltage drop of less than 1.0 V when
a current of 5 A passes through it. Using the data in Table (1), compute the
minimum diameter of the wire.
Solution
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2) Consider a wire, 3 mm in diameter and 2 m long. Answer the following questions.
Person 1: What is the resistance in the wire if it is made of copper?
Person 2: What is the resistance in the wire if it is made of stainless steel?
Exchange the results of your calculations, check them, and use them to make the
following calculations, assuming that a potential difference of 0.05 V is placed across
the ends of the wire and the σCu = 5.85 * 107 (mho/m) and σSS = 0.14*107 (mho/m).
Person 1: If the wire is made of stainless steel, calculate the current flow, current
density, and magnitude of the electric field.
Person 2: If the wire is made of copper, calculate the current flow, current density, and
magnitude of the electric field.
Solution
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H.W. Solution for Lect. (1)
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3) The power lost in a 2-mm-diameter copper wire is to be less than 250 W when a 5-A
current is flowing in the circuit. What is the maximum length of the wire?
Solution
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H.W. Solution for Lect. (1)
4) Suppose we estimate that the mobility of electrons in silver is 75 cm2/V.s. Estimate
the fraction of the valence electrons (n/nT) that are carrying an electrical charge. Not;
n is number of electrons that contributed in conductivity, n T is total number of
valence electron, n/nT is the ratio part to the total.
Solution
5) A current density of 5000 A/cm2 is applied to a magnesium wire. If half of the
valence electrons serve as charge carriers, calculate the average drift velocity of the
electrons.
Solution
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