Jadeen says that you can increase the resistance of a copper wire by hammering the wire to make it narrower and longer. Arnell says that you can increase its resistance by heating the wire. Which one, if either, is correct, and why?
a. Arnell, because the conductivity of the wire increases when it is heated.
b. Arnell, because the conductivity of the wire decreases when it is heated.
c. Jadeen, because the conductivity of a wire is directly proportional to its area and inversely proportional to its length.
d. Jadeen, because the conductivity of a copper wire does not increase when it is hammered.
e. Both are correct because (b) and (d) are both correct.
[Ques. 2] Light bulb A is rated at 60 W and light bulb B is rated at 100 W. Both are designed to operate at 110 V. Which statement is correct?
a. The 60 W bulb has a greater resistance and greater current than the 100 W bulb.
b. The 60 W bulb has a greater resistance and smaller current than the 100 W bulb.
c. The 60 W bulb has a smaller resistance and smaller current than the 100 W bulb.
d. The 60 W bulb has a smaller resistance and greater current than the 100 W bulb.
e. We need to know the resistivities of the filaments to answer this question.
[Ques. 3] In the Drude model of electrical conduction, the current density is NOT directly proportional to
a. the average time interval between successive collisions.
b. the number of charge carriers per unit volume.
c. the square of the electron charge.
d. the electric field present in the wire.
e. the resistivity of the wire.
[Ques. 4] In the Drude model of electrical conduction, the current density is directly proportional to
a. the average time interval between successive collisions.
b. the number of charge carriers per unit volume.
c. the square of the electron charge.
d. the electric field present in the wire.
e. the product of all four quantities listed above.
[Ques. 5] The electron density in copper is 8.49 1028 electrons/m3 . The electron charge is e = 1.60 1019 C. When a 1.00 A current is present in a copper wire with a 0.40 cm2 cross-section, the electron drift velocity, in m/s, with direction defined relative to the current density, is
a. 1.84 106.
b. +1.84 106.
c. 1.84.
d. 5.43 105.
e. +5.43 105.
[Ques. 6] A nichrome wire and an aluminum wire, each with the same initial resistance, have the same change in resistance when heated separately. (Al = 2.82 108 / m; Al = 3.9 103 / C; nichrome = 1.50 106 / m; nichrome = 0.40 103 / C.) The ratio of the temperature change of the nichrome wire to the temperature change of the aluminum wire is
a. 0.019.
b. 0.10.
c. 0.18.
d. 9.8.
e. 53.
[Ques. 7] The temperature coefficient of resistivity of iron is 5.0 103 / C; that of carbon is 0.50 103 / C. When an iron wire and a carbon rod, each having the same 10 resistance at 20C, are cooled from that temperature to 80C, the new ratio of the resistance of the carbon rod to the resistance of the iron wire at the lower temperature is
a. 0.10.
b. +1.9.
c. +2.1.
d. 10.
e. +10.
[Ques. 8] A small bulb is rated at 7.50 W when operated at 125 V. The tungsten filament has a temperature coefficient of resistivity = 4.50 103 / C. When the filament is hot and glowing, its temperature is seven times room temperature (20 C). What is the resistance of the filament (in ohms) at room temperature?
a. 234
b. 1 350
c. 2 080
d. 4 530
e. 5 630
[Ques. 9] A small bulb is rated at 7.5 W when operated at 125 V. Its resistance (in ohms) is
a. 0.45.
b. 7.5.
c. 17.
d. 940.
e. 2 100.
[Ques. 10] If a mile of 24-gauge copper wire has a resistance of 0.14 k and the resistivity of copper is 1.7 108 / m, what is the diameter of the wire? (1 mile = 1.6 km)
a. 0.40 mm
b. 0.50 mm
c. 0.63 mm
d. 0.80 mm
e. 0.25 mm
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