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Chapter 18: Q3Q (page 755)
How can there be a nonzero electric field inside a wire in a circuit? Isn鈥檛 the electric field inside a metal always zero?
The field inside a wire in a circuit is non zero due to the absence of an opposing electric field because there is no accumulation of charges anywhere
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In the few nanoseconds before the steady state is established in a circuit consisting of a battery, copper wires, and a single bulb, is the current the same everywhere in the circuit? Explain.
What would be the potential difference across the thin resistor in Figure 18.103 if the battery emf is ? Assume that the electric field in the thick wires is very small (so that the potential differences along the thick wires are negligible). Do you have enough information to determine the current in the circuit?
Inside a chemical battery it is not actually individual electrons that are transported from the + end to the 鈥� end. At the + end of the battery an 鈥渁cceptor鈥� molecule picks up an electron entering the battery, and at the 鈥� end a different 鈥渄onor鈥� molecule gives up an electron, which leaves the battery. Ions rather than electrons move between the two ends to support the charge inside the battery.
When the supplies of acceptor and donor molecules are used up in a chemical battery, the battery is dead because it can no longer accept or electron. The electron current in electron per second times the number of seconds of battery life, is equal to the number of donor molecules in the battery.
A flashlight battery contains approximately half a mole of donor molecules. The electron current through a thick filament bulb powered by two flashlight batteries in series is about 0.3 A. About how many hours will the batteries keep this bulb lit?
In the circuit shown in Figure 18.87, bulbs 1 and 2 are identical in mechanical construction (the filaments have the same length and the same cross-sectional area), but the filaments are made of different metals. The electron mobility in the metal used in bulb 2 is three times as large as the electron mobility in the metal used in bulb 1, but both metals have the same number of mobile electrons per cubic meter. The two bulbs are connected in series to two batteries with thick copper wires (like your connecting wires).
(a)In bulb 1, the electron current is and the electric field is . In terms of these quantities, determine the corresponding quantities and for bulb 2, and explain your reasoning.
(b)When bulb 2 is replaced by a wire, the electron current through bulb 1 is and the electric field in bulb 1 is . How big is in terms of ? Explain your answer, including explicit mention of any approximations you must make. Do not use ohms or series-resistance equations in your explanation, unless you can show in detail how these concepts follow from the microscopic analysis introduced in this chapter.
(c)Explain why the electric field inside the thick copper wires is very small. Also explain why this very small electric field is the same in all of the copper wires, if they all have the same cross-sectional area.
(d)Figure 18.88 is a graph of the magnitude of the electric field at each location around the circuit when bulb 2 is replaced by a wire. Copy this graph and add to it, on the same scale, a graph of the magnitude of the electric field at each location around the circuit when both bulbs are in the circuit. The very small field in the copper wires has been shown much larger than it really is in order to give you room to show how that small field differs in the two circuits.
What is the most important general difference between a system in steady state and a system in equilibrium?
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