17.6 (a) Briefly explain why Cv rises with increasing temperature at temperatures
near 0 K.
(b) Briefly explain why Cv becomes virtually independent of temperature at temperatures far removed from 0 K.
17.10 A 0.1 m rod of a metal elongates 0.2 mm on heating from 20 to 100_C .
Determine the value of the linear coefficient of thermal expansion for this material.
17.11 Briefly explain thermal expansion using the potential energy-versus-interatomic
spacing curve.
17.12 When a metal is heated its density decreases. There are two sources that give
rise to this diminishment of _: (1) the thermal expansion of the solid, and (2) the formation of vacancies (Section 5.2). Consider a specimen of copper at room temperature (20_C) that has a density of 8.940 g/cm3. (a) Determine its density upon heating to 1000_C when only thermal expansion is considered. And (b) repeat the calculation when the introduction of vacancies is taken into account. Assume that the energy of vacancy formation is 0.90 eV/atom, and that the volume coefficient of thermal expansion, _v, is equal to 3_l .
17.16 (a) Calculate the heat flux through a sheet of steel 10mm thick if the
temperatures at the two faces are 300 and 100℃; assume steady-state heat flow (b) What is the heat loss per hour if the area of the sheet is 0.25 m2? (c) What will be the heat loss per hour if soda–lime glass instead of steel is used? (d) Calculate the heat loss per hour if steel is used and the thickness is increased to 20 mm
17.18 (a) The thermal conductivity of a single-crystal specimen is slightly greater
than a polycrystalline one of the same material. Why is this so? (b) The thermal conductivity of a plain carbon steel is greater than for a stainless steel. Why is this so?
17.19 Briefly explain why the thermal conductivities are higher for crystalline than
noncrystalline ceramics.
17.20 Briefly explain why metals are typically better thermal conductors than ceramic
materials.
17.21 (a) Briefly explain why porosity decreases the thermal conductivity of ceramic
and polymeric materials, rendering them more thermally insulative. (b) Briefly explain how the degree of crystallinity affects the thermal conductivity of polymeric materials and why.
17.22 For some ceramic materials, why does the thermal conductivity first decrease
and then increase with rising temperature?
17.23 For each of the following pairs of materials, decide which has the larger thermal
conductivity. Justify your choices.
(a) Pure silver; sterling silver (92.5 wt%Ag– 7.5 wt% Cu). (b) Fused silica; polycrystalline silica.
(c) Linear polyethylene (Mn _ 450,000 g/mol); lightly branched polyethylene (Mn _ 650,000 g/mol).
(d) Atactic polypropylene (Mw _ 106 g/mol); isotactic polypropylene (Mw _ 5 _ 105 g/mol).
18.1 A coil of wire 0.20 m long and having 200 turns carries a current of 10 A.
(a) What is the magnitude of the magnetic field strength H? (b) Compute the flux density B if the coil is in a vacuum.
(c) Compute the flux density inside a bar of titanium that is positioned within the coil. The susceptibility for titanium is found in Table 18.2. (d) Compute the magnitude of the magnetization M.
18.5 (a) Explain the two sources of magnetic moments for electrons.
(b) Do all electrons have a net magnetic moment? Why or why not? (c) Do all atoms have a net magnetic moment? Why or why not?
18.6 The magnetic flux density within a bar of some material is 0.435 tesla at an H
field of 3.44 _ 105 A/m. Compute the following for this material: (a) the
magnetic permeability, and (b) the magnetic susceptibility. (c) What type(s) of magnetism would you suggest as being displayed by this material? Why?
18.8 Compute (a) the saturation magnetization and (b) the saturation flux density for
cobalt, which has a net magnetic moment per atom of 1.72 Bohr magnetons and a density of 8.90 g/cm3.
18.9 Confirm that there are 2.2 Bohr magnetons associated with each iron atom, given
that the saturation magnetization is 1.70 _ 106 A/m, that iron has a BCC crystal structure, and that the unit cell edge length is 0.2866 nm.
18.11 There is associated with each atom in paramagnetic and ferromagnetic materials
a net magnetic moment. Explain why ferromagnetic materials can be permanently magnetized whereas paramagnetic ones cannot.
18.12 Cite the major similarities and differences between ferromagnetic and
ferromagnetic materials.
18.16 The chemical formula for manganese ferrite may be written as (MnFe2O4)8
because there are eight formula units per unit cell. If this material has a
saturation magnetization of 5.6 _ 105 A/m and a density of 5.00 g/cm3, estimate the number of Bohr magnetons associated with each Mn2_ ion.
18.19 Briefly explain why the magnitude of the saturation magnetization decreases
with increasing temperature for ferromagnetic materials, and why ferromagnetic behavior ceases above the Curie temperature.
18.20 Briefly describe the phenomenon of magnetic hysteresis, and why it occurs for
ferromagnetic and ferrimagnetic materials.
18.21 Schematically sketch on a single plot the B-versus-H behavior for a
ferromagnetic material (a) at 0 K, (b) at a temperature just below its Curie temperature, and (c) at a temperature just above its Curie temperature. Briefly explain why these curves have different shapes.
18.23 Cite the differences between hard and soft magnetic materials in terms of both
hysteresis behavior and typical applications.
18.25 Figure 18.25 shows the B-versus-H curve for a steel alloy
(a) What is the saturation flux density?
(b) What is the saturation magnetization?
(c) What is the remanence? (d) What is the coercivity? (e) On the basis of the data in Tables 18.5 and 18.6, would you classify this material as a soft or hard magnetic material? Why? 18.26 A ferromagnetic material has
a remanence of 1.25 teslas and a coercivity of 50,000 A/m. Saturation is
achieved at a magnetic field intensity of 100,000 A/m, at which the flux density is 1.50 teslas. Using these data, sketch the entire hysteresis curve in the range H _ _100,000 to _100,000 A/m. Be sure to scale and label both coordinate axes.
18.32 For a superconducting material at a temperature T below the critical
temperature TC, the critical field HC(T), depends on temperature according to the relationship
where HC(0) is the critical field at 0 K.
(a) Using the data in Table 18.7, calculate the critical magnetic fields for tin at 1.5 and 2.5 K.
(b) To what temperature must lead be cooled in a magnetic field of 20,000 A/m for it to be superconductive?
19.3 Visible light having a wavelength of 6×10-7m appears orange. Compute the
frequency and energy of a photon of this light.
19.4 Distinguish between materials that are opaque, translucent, and transparent in
terms of their appearance and light transmittance.
19.5 (a) Briefly describe the phenomenon of electronic polarization by
electromagnetic radiation.
(b) What are two consequences of electronic polarization in transparent materials?
19.6 (a) In ionic materials, how does the size of the component ions affect the extent
of electronic polarization?
(b) Which of the following oxide materials when added to fused silica (SiO2 )
will increase its index of refraction: Al2O3 , TiO2 , NiO, MgO? Why? You may find Table 3.4 helpful.
19.7 (a) Briefly explain why metals are opaque to electromagnetic radiation having
photon energies within the visible region of the spectrum.
(b) Why are metals transparent to high-frequency x-ray and _-ray radiation? 19.8 Can a material have an index of refraction less than unity? Why or why not? 19.11 Using the data in Table 19.1, estimate the dielectric constants for silica glass
(fused silica),soda–lime glass, polytetrafluoroethylene, polyethylene, and polystyrene, and compare these values with those cited in Table 12.4. Briefly explain any discrepancies.
19.12 Briefly describe the phenomenon of dispersion in a transparent medium.
19.14 Briefly explain how reflection losses of transparent materials are minimized by
thin surface coatings.
19.15 Briefly describe the three absorption mechanisms in nonmetallic materials. 19.16 Will the elemental semiconductors silicon and germanium be transparent to
visible light? Why or why not? Their band gap energies are given in Table 12.2. 19.18 Briefly explain why the magnitude of the absorption coefficient (_ in Equation
19.18) depends on the radiation wavelength.
19.19 The fraction of nonreflected radiation that is transmitted through a 10-mm
thickness of a transparent material is 0.90. If the thickness is increased to 20 mm, what fraction of light will be transmitted?
19.21 The transmissivity T of a transparent material 20 mm thick to normally incident
light is 0.85. If the index of refraction of this material is 1.6, compute the
thickness of material that will yield a transmissivity of 0.75. All reflection losses should be considered.
19.22 Briefly explain what determines the characteristic color of (a) a metal and (b) a
transparent nonmetal.
19.23 Briefly explain why some transparent materials appear colored while others are
colorless.
19.24 The index of refraction of quartz is anisotropic. Suppose that visible light is
passing from one grain to another of different crystallographic orientation and at normal incidence to the grain boundary. Calculate the reflectivity at the boundary if the indices of refraction for the two grains are 1.544 and 1.553.
19.25 Briefly explain why amorphous polymers are transparent, while predominantly
crystalline polymers appear opaque or, at best, translucent.
19.26 (a) In your own words describe briefly the phenomenon of luminescence.
(b) What is the distinction between fluorescence and phosphorescence?
英文思考题、习题部分参考答案
2.6 L: s:200(1/2);200(-1/2)
p:210(1/2);210(-1/2); 21-1(1/2);21-1(-1/2); 211(1/2);211(-1/2) M: s:300(1/2);300(-1/2)
p:310(1/2);310(-1/2); 31-1(1/2);31-1(-1/2); 311(1/2);311(-1/2)
d: 320(1/2);320(-1/2); 32-1(1/2);32-1(-1/2); 321(1/2);321(-1/2); 32-2(1/2);32-2(-1/2); 322(1/2);322(-1/2) 2.7 Fe2+ : 1s22s22p63s23p63d6 Fe3+ : 1s22s22p63s23p63d5 Cu+ : 1s22s22p63s23p63d10
Ba2+ : 1s22s22p63s23p63d104s24p64d105s25p6 Br - : 1s22s22p63s23p63d104s24p6 S 2- : 1s22s22p63s23p6 2.19 TiO2, %IC=63.2% ZnTe, %IC=6.05% CsCl, %IC=73.4% InSb, %IC=1.0% MgCl2, %IC=55.5% 2.21 Ge : 4 P : 3 Se : 2 Cl : 1 3.4 a = 4R /3
3.6 BCC: APF = 0.68 3.27 0.414
3.48
3.50 （a）direction 1, [012]
direction 2, [112]
（b）Plane 1， (010)
Plane 2， (221)
3.51 （a）[110]
b）[121] （