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CHAPTER 21 OPTICAL PROPERTIES PROBLEM SOLUTIONS 21.1 Similarities between photons and phonons are: 1) Both may be described as being wave-like in nature. 2) The energy for both is quantized. Differences between photons and phonons are: 1) Phonons are elastic waves that exist within solid materials. Photons are electromagnetic energy packets that may exist in solid materials, as well as in other media. 2) There is a considerable disparity between the velocities of photons and phonons. The velocity of a photon is the same as the velocity of light in the particular medium; for a phonon, its velocity is that of sound. 21.2 From the classical perspective, electromagnetic radiation is wave-like in character, and the possible energies of the radiation are continuous. From the quantum-mechanical perspective, electromagnetic radiation is dual-like in character (being both wave-like and particle-like), and not all energies are possible (i.e., energy is quantized). 21.3 In order to compute the frequency of a photon of orange light, we must use Equation (21.2) as ν = c λ = 3 x 10 8 m /s 6 x 10 7 m = 5 x 10 14 s -1 Now, for the energy computation, we employ Equation (21.3) as follows: E = hc λ = 6.63 x 10 34 J -s ( ) 3 x 10 8 m / s ( ) 6 x 10 7 m = 3.31 x 10 -19 J (2.07 eV) 21.4 Opaque materials are impervious to light transmission; it is not possible to see through them. Light is transmitted diffusely through translucent materials (there is some internal light scattering). Objects are not clearly distinguishable when viewed through a translucent material. 1
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