Chapter 27: Q. 23 (page 762)
23. A -mm-diameter silver wire carries a current. What are (a) the electric field and (b) the electron drift speed in the wire?
Short Answer
(a) The electric field is .
(b) The electron drift speed in the wire is .
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Chapter 27: Q. 23 (page 762)
23. A -mm-diameter silver wire carries a current. What are (a) the electric field and (b) the electron drift speed in the wire?
(a) The electric field is .
(b) The electron drift speed in the wire is .
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75. A capacitor is charged to , then connected in parallel with a resistor. The capacitor will discharge because the resistor provides a conducting pathway between the capacitor plates, but much more slowly than if the plates were connected by a wire. Let be the instant the fully charged capacitor is first connected to the resistor. At what time has the capacitor voltage decreased by half, to ?
Hint: The current through the resistor is related to the rate at which charge is leaving the capacitor. Consequently, you'll need a minus sign that you might not have expected.
17. What is the mean time between collisions for electrons in (a) an aluminum wire and (b) an iron wire?
A wire of radius has a current density that increases linearly with distance from the center of the wire: , where is a constant. Find an expression for in terms of and the total currentcarried by the wire.
74. FIGURE CP27.74 shows a wire that is made of two equal diameter segments with conductivities and . When current passes through the wire, a thin layer of charge appears at the boundary between the segments.
a. Find an expression for the surface charge density on the boundary. Give your result in terms of , and the wire's cross-section area .
b. A -mm-diameter wire made of copper and iron segments carries a current. How much charge accumulates at the boundary between the segments?
II You need to design a fuse that "blows" if the current exceeds . The fuse material in your stockroom melts at a current density of . What diameter wire of this material will do the job?
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