201 Week 4 2008 Posted

201 Week 4 2008 Posted - Callister Web Chapter 21: Optical...

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Chapter 21 - 1 ISSUES TO ADDRESS. .. What happens when light shines on a material ? Optical applications: -- photoconductivity -- solar cell -- optical communications fibers Why are some materials transparent and others not? Callister Web Chapter 21: Optical Properties
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Chapter 21 - 2 Optical Properties Light has both particulate and wavelike properties – Photons - with mass
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Chapter 21 - 3 Incident light is either reflected, absorbed, or transmitted: Light Interaction with Solids Optical classification of materials: Adapted from Fig. 21.10, Callister 6e . (Fig. 21.10 is by J. Telford, with specimen preparation by P.A. Lessing.) single crystal polycrystalline dense polycrystalline porous Transparent Translucent Opaque Incident: I 0 Absorbed: I A Transmitted: I T Scattered: I S Reflected : I R
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Chapter 21 - 4 Absorption of photons by electron transition: Metals have a fine succession of energy states. Near-surface electrons absorb visible light. Adapted from Fig. 21.4(a), Callister 7e . Optical Properties of Metals: Absorption Energy of electron Planck’s constant (6.63 x 10 -34 J/s) freq. of incident light filled states unfilled states Δ E = h ν required! I o
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Chapter 21 - 5 Light Absorption
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Chapter 21 - 6 Reflectivity = I R / I o is between 0.90 and 0.95. Reflected light is same frequency as incident. Metals appear reflective (shiny)! Adapted from Fig. 21.4(b), Callister 7e . Optical Properties of Metals: Reflection Electron transition emits a photon. re-emitted photon from material surface Energy of electron filled states unfilled states Δ E I R “conducting” electron
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Chapter 21 - 7 Reflectivity, R Reflection – Metals reflect almost all light – Copper & gold absorb in blue & green => gold color Example: Diamond
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201 Week 4 2008 Posted - Callister Web Chapter 21: Optical...

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