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Chapter 18: Q5Q (page 755)
Since there is an electric field inside a wire in a circuit, why don鈥檛 the mobile electrons in the wire accelerate continuously?
Electrons in a wire don't accelerate continuously because the backward force due to resistance cancels out the forward force from the external electric field.
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In the circuit shown in Figure 18.110, the two thick wires and the thin wire are made of Nichrome.
(a) Show the steady-state electric field at indicated locations, including in the thin wire. (b) Carefully draw pluses and minuses on your own diagram to show the approximate surface-charge distribution in the steady state. Make your drawing show the differences between regions of high surface-charge density and regions of low surface-charge density. (c) The emf of the battery is. In Nichrome, there are 28 mobile electrons per m3, and the mobility of mobile electrons is -5. Each thick wire has a length of L1 and a cross-sectional area of A1 -8 m2. The thin wire has a length of L2 and a cross-sectional area of A2-8m2. (The total length of the three wires is )Calculate the number of electrons entering the thin wire every second in the steady state. Do not make any approximations, and do not use Ohm鈥檚 law or series-resistance equations. State briefly where each of your equations comes from.
A steady-state current flows through the Nichrome wire in the circuit shown in Figure 18.90. Before attempting to answer the following questions, draw a copy of this diagram. All of the locations indicated by letters are inside the wire.
(a)On your diagram, show the electric field at the locations indicated, paying attention to relative magnitude.
(b)Carefully draw pluses and minuses on your diagram to show the approximate surface charge distribution that produces the electric field you drew. Make your drawing show clearly the differences between regions of high surface charge density and regions of low surface-charge density. Use your diagram to determine which of the following statements about this circuit are true.
(1) There is some excess negative charge on the surface of the wire near location B.
(2) Inside the metal wire the magnitude of the electric field is zero.
(3) The magnitude of the electric field is the same at locations Gand C.
(4) The electric field points to the left at location G.
(5) There is no excess charge on the surface of the wire.
(6) There is excess charge on the surface of the wire near the batteries but nowhere else.
(7) The magnitude of the electric field inside the wire is larger at location Gthan at location C.
(8) The electric field at location Dpoints to the left.
(9) Because the current is not changing, the circuit is in static equilibrium.
There are very roughly the same number of iron atoms per m3 as there are copper atoms per m3 , but copper is a much better conductor than iron. How does uiron compare with ucopper?
At a typical drift speed of , an electron traveling at that speed would take about to travel through one of your connecting wires. Why, then, does the bulb light immediately when the connecting wire is attached to the battery?
Question: Three identical light bulbs are connected to two batteries as shown in Figure 18.106. (a) To start the analysis of this circuit you must write energy conservation (loop) equations. Each equation must involve a round-trip path that begins and ends at the same location. Each segment of the path should go through a wire, a bulb, or a battery (not through the air). How many valid energy conservation (loop) equations is it possible to write for this circuit? (b) Which of the following equations are valid energy conservation (loop) equations for this circuit? refers to the electric field in bulb 1; refers to the length of a bulb filament. Assume that the electric field in the connecting wires is small enough to neglect.
(1) , (2) , (3), (4), (5), (6), (7). (c) It is also necessary to write charge conservation equations (node) equations. Each such equation must relate electron current flowing into a node to electron current flowing out of a node. Which of the following are valid charge conservation equations for this circuit? (1), (2), (3). Each battery has an emf of . The length of the tungsten filament in each bulb is . The radius of the filament is(it is very thin!). The electron mobility of tungsten is localid="1668588909714" . Tungsten has localid="1668588927161" mobile electrons per cubic meter. Since there are three unknown quantities, we need three equations relating these quantities. Use any two valid energy conservation equations and one valid charge conservation equation to solve for localid="1668588943223" and localid="1668588965567" .
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