Callister - An introduction - 8th edition

870 • Chapter 21 / Optical Properties
periclase (MgO), poly(methyl methacrylate),
and polypropylene, and compare these values
with those cited in the following table. Briefly
explain any discrepancies.
Dielectric Constant
Material
(1 MHz)
Borosilicate glass 4.65
Periclase 9.65
Poly(methyl methacrylate) 2.76
Polypropylene 2.30
21.10 Briefly describe the phenomenon of dispersion
in a transparent medium.
Reflection
21.11 It is desired that the reflectivity of light at
normal incidence to the surface of a transparent
medium be less than 6.0%. Which of
the following materials in Table 21.1 are
likely candidates: silica glass, Pyrex glass,
corundum, spinel, polystyrene, and polytetrafluoroethylene?
Justify your selection(s).
21.12 Briefly explain how reflection losses of
transparent materials are minimized by thin
surface coatings.
21.13 The index of refraction of corundum
(Al 2 O 3 ) 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 1.757 and 1.779 in the direction of light
propagation.
Absorption
21.14 Zinc telluride has a band gap of 2.26 eV.
Over what range of wavelengths of visible
light is it transparent?
21.15 Briefly explain why the magnitude of the absorption
coefficient ( b in Equation 21.18)
depends on the radiation wavelength.
21.16 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?
Transmission
21.17 Derive Equation 21.19, starting from other
expressions given in the chapter.
21.18 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.
Color
21.19 Briefly explain what determines the characteristic
color of (a) a metal and (b) a transparent
nonmetal.
21.20 Briefly explain why some transparent
materials appear colored whereas others are
colorless.
Opacity and Translucency in Insulators
21.21 Briefly describe the three absorption mechanisms
in nonmetallic materials.
21.22 Briefly explain why amorphous polymers
are transparent, while predominantly crystalline
polymers appear opaque or, at best,
translucent.
Luminescence
Photoconductivity
Lasers
21.23 (a) In your own words, briefly describe the
phenomenon of luminescence.
(b) What is the distinction between fluorescence
and phosphorescence?
21.24 In your own words, briefly describe the phenomenon
of photoconductivity.
21.25 Briefly explain the operation of a photographic
lightmeter.
21.26 In your own words, describe how a ruby laser
operates.
21.27 Compute the difference in energy between
metastable and ground electron states for
the ruby laser.
Optical Fibers in Communications
21.28 At the end of Section 21.14 it was noted that
the intensity of light absorbed while passing
through a 16-kilometer length of optical