Chapter 18: Q5Q (page 755)
Since there is an electric field inside a wire in a circuit, why don’t 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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Why don’t all mobile electrons in a metal have exactly the same speed?
The circuit shown in Figure 18.107 consists of a single battery, whose emf is , and three wires made of the same material but having different cross-sectional areas. Each thick wire has a cross-sectional area and is long. The thin wire has a cross-sectional area and is long. In this metal, the electron mobility is , and there are mobile electrons/m3.
(a) Which of the following statements about the circuit in the steady state are true? (1) At location B, the electric field points toward the top of the page. (2) The magnitude of the electric field at locations F and C is the same. (3) The magnitude of the electric field at locations D and F is the same. (4) The electron current at location D is the same as the electron current at location F . (b) Write a correct energy conservation (loop) equation for this circuit, following a path that starts at the negative end of the battery and goes counterclockwise. (c) Write this circuit's correct charge conservation (node) equation. (d) Use the appropriate equation(s), plus the equation relating electron current to electric field, to solve for the magnitudes EDand EF of the electric field at locations D and F . (e) Use the appropriate equation(s) to calculate the electron current at location D in the steady state.
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" .
How can there be a nonzero electric field inside a wire in a circuit? Isn’t the electric field inside a metal always zero?
State your own theoretical and experimental objections to the following statement: In a circuit with two thick-filament bulbs in series, the bulb farther from the negative terminal of the battery will be dimmer, because some of the electron current is used up in the first bulb. Cite relevant experiments.
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