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Chapter 18: Q7Q (page 755)

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?

Short Answer

Expert verified

The ucopper is greater than uiron

Step by step solution

01

Given data

Copper is a better conductor than iron.

02

Define the concept for the mobility

The mobility in a conductor of cross sectional area A and n number of atoms per unit volume, through which a current i passes on application of electric field E, is defined as follows:

u=inAE ..... (i)

03

Determine the mobility of copper to that of iron

From equation (i) it is evident that for equal number density, area and applied electric field, the conductor which allows more current has better mobility that is the material which is more conducting has larger mobility. Thus, copper has larger mobility that is given as:

ucopper>uiron

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Most popular questions from this chapter

The emf of a particular flashlight battery is 1.7 V. If the battery is 4.5 cm long and radius of cylindrical battery is 1 cm, estimate roughly the amount of charge on the positive end plate of the battery.

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?

A Nichrome wire 30 cm long and 0.25 mm in diameter is connected to a 1.5 V flashlight battery. What is the electric field inside the wire? Why you don’t have to know how the wire is bent? How would your answer change if the wire diameter change were 0.35 mm? (Not that the electric field in the wire is quiet small compared to the electric field near a charged tape.)

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.

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 is1.5V. In Nichrome, there are n=9×1028 mobile electrons per m3, and the mobility of mobile electrons is μ=7×10-5(m/s)(V/m). Each thick wire has a length of L1 =20cm=0.2m and a cross-sectional area of A1 =9×10-8 m2. The thin wire has a length of L2=5cm=0.05m and a cross-sectional area of A2=1.5×10-8m2. (The total length of the three wires is 45cm)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’s law or series-resistance equations. State briefly where each of your equations comes from.
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