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CH26
Start Date:
6 Feb 2009 at 04:00 PM
Due Date:
11 Feb 2009 at 11:00 PM
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*Chapter 26, Problem 24 GO
The figure gives the electric potential V(x) along a copper wire carrying uniform current, from a point of higher
potential Vs = 8.00 μVat x = 0 to a point of zero potential at xs = 2.20 m. The wire has a radius of 1.90 mm, and
copper has a resistivity of 1.69 × 10-8 Ω·m. What is the current (in A) in the wire?
Number
Units
the tolerance is +/-5%
*Chapter 26, Problem 34 GO
Flying Circus of Physics
The figure shows a swimmer at distance D = 40.0 m from a lightning strike to the water, with current I = 78.0 kA.
The water has resistivity 30 Ω·m, the width of the swimmer along a radial line from the strike is 0.900 m, and his
resistance across that width is 5.50 kΩ. Assume that the current spreads through the water over a hemisphere
centered on the strike point. What is the current (in A) through the swimmer?
Number
Units
the tolerance is +/-5%
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*Chapter 26, Problem 50 GO
The current-density magnitude in a certain circular wire is J = (3.00 × 1010 A/m4)r2, where r is the radial distance
out to the wire's radius of 1.50 mm. The potential applied to the wire (end to end) is 67.0 V. How much energy is
converted to thermal energy in 1.40 h?
Number
Units
the tolerance is +/-5%
*Chapter 26, Problem 66 GO
The current density in a copper wire of radius 0.800 mm is uniform. The wire's length is 4.50 m, the end-to-end
potential difference is 0.180 V, and the density of conduction electrons is 8.00 × 1028 m-3. How long does an electron
take (on the average) to travel the length of the wire?
Number
Units
the tolerance is +/-5%
*Chapter 26, Problem 74
A caterpillar of length 4.0 cm crawls in the direction of electron drift along a 5.4-mm-diameter bare copper wire that
carries a uniform current of 41 A. (a) What is the potential difference (in mV) between the two ends of the
caterpillar? (b) Is its tail positive (type "1") or negative (type "0") relative to its head? (c) How much time (in s)
does the caterpillar take to crawl 3.4 cm if it crawls at the drift speed of the electrons in the wire? (The number of
charge carriers per unit volume is 8.49 × 1028 m-3 and resistivity of copper is 1.69 × 10-8 Ω·m.)
(a) Number
Units
(b)
(c) Number
Units
Answer a1: the tolerance is +/-5%
Answer b1: exact number, no tolerance
Answer c1: the tolerance is +/-5%
Test Bank, Question 19
The resistance of a rod does NOT depend on:
its temperature
its material
its length
its conductivity
shape of its (fixed) cross-sectional area
Test Bank, Question 31
For an ohmic substance, the resistivity depends on:
the electric field
the potential difference
the current density
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the electron mean free time
the cross-sectionalarea of the sample
Test Bank, Question 41
An ordinary light bulb is marked "60 watt, 120 volt". Its resistance is:
60
120
180
240
15
Chapter 26, Concept Question 2
Figure 26.17 shows plots of the current i through a certain cross section of a wire over four different time periods.
Rank the periods according to the net charge that passes through the cross section during the period, greatest first. If
multiple periods rank equally, use the same rank for each, then exclude the intermediate ranking (i.e. if objects A, B,
and C must be ranked, and A and B must both be ranked first, the ranking would be A:1, B:1, C:3). If all periods
rank equally, rank each as '1'.
(a)
(b)
(c)
(d)
1. Greatest
2. Second greatest
3. Third greatest
4. Fourth greatest
Chapter 26, Concept Question 4
Figure 26.19 shows cross sections through three wires of identical length and material; the sides are given in
millimeters.
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Rank the wires according to their resistance (measured end to end along each wire's length), greatest first. If
multiple wires rank equally, use the same rank for each, then exclude the intermediate ranking (i.e. if objects A, B,
and C must be ranked, and A and B must both be ranked first, the ranking would be A:1, B:1, C:3). If all wires rank
equally, rank each as '1'.
(a)
(b)
(c)
1. Greatest
2. Second greatest
3. Third greatest
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