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Chapter 18: Q8Q (page 755)

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.

Short Answer

Expert verified

The region in the circuit before the light bulb has more current than the region in the circuit after the light bulb

Step by step solution

01

Given data

A circuit consists of a battery, copper wire and a single bulb.

02

Determine the energy transfer in a light bulb

In a light bulb, electrical energy of the mobile electrons are converted to heat and light energy.

03

Comparison of current in a circuit before steady state

In a light bulb, a part of the electrical energy of the mobile electrons is lost to produce heat and light. Thus the electrons coming out of the bulb have less energy and thus region has less current since current is the rate of flow of charges.

Thus, before steady state is achieved, the region in the circuit before the light bulb has more current than the region in the circuit after the light bulb.

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Most popular questions from this chapter

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? E1refers to the electric field in bulb 1; L refers to the length of a bulb filament. Assume that the electric field in the connecting wires is small enough to neglect.

(1) +E2L-E3L=0, (2) E1L-E3L=0, (3)+2emf-E2L-E3L=0, (4)E1L-E2L=0, (5)+2emf-E1L-E2L=0, (6)+2emf-E1L-E3L=0, (7)+2emf-E1L-E2L-E3L=0. (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)i1=i3, (2)i1=i2, (3)i1=i2+i3. Each battery has an emf of 1.5V. The length of the tungsten filament in each bulb is 0.008m. The radius of the filament is5×10-6m(it is very thin!). The electron mobility of tungsten is localid="1668588909714" 1.8×10-3(m/s)/(V/m). Tungsten has localid="1668588927161" 6×1028mobile 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" E1,E2,i1and localid="1668588965567" i2.

Question:In figure 18.102 suppose that VC-VF=8 V and VD-VE=4.5 V.

(a) What is the potential difference VC-VD?

(b) If the element between the battery C and D is a battery, is the + end of the battery at C or D?

What would be the potential difference VC-VBacross the thin resistor in Figure 18.103 if the battery emf is3.5V ? 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?

In the circuit shown figure 18.108, two thick copper wires connect a 1.5 V battery to a Nichrome wire. Each thick connecting wire is 17 cm long and has a radius of 9 mm. Copper has 8.4×1028mobile electrons per cubic meter and electron mobility. The Nichrome wire is 8 cm long and has a radius of 3 mm. Nichrome has 9×1028mobile electrons per cubic meter and electron mobility of 7×10-5(ms)(Vm).

(a) What is the magnitude of the electric field in the thick copper wire?

(b) What is the magnitude of the electric field in the thin Nichrome wire?

What is the most important general difference between a system in steady state and a system in equilibrium?
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