2010-04-14 Chapter 21 Optical Properties

2010-04-14 Chapter 21 Optical Properties - Chapter 21 1...

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Unformatted text preview: Chapter 21 - 1 ISSUES TO ADDRESS... • What happens when light shines on a material ? • Why do materials have characteristic colors? • Optical applications:-- luminescence-- photoconductivity-- solar cell-- optical communications fibers • Why are some materials transparent and others not? Chapter 21: Optical Properties Chapter 21 - 2 Light: A Particle, a Wave, or Both? • Electromagnetic Radiation: a form of energy that is transmitted through space at enormous velocities. • Light: EMR in the UV/Vis region. – A wave: properties of wavelength, frequency, velocity, and amplitude. • Fails to account for absorption and emission of radiant energy. – Photons or quanta: discreet packets of energy or particles Chapter 21 - 3 Wave Properties Frequency ( ν ): the number of oscillations of the electric field vector per unit time = 1/p; depends upon source of emmision but not upon medium. Period (p): the time required for successive maxima, or minima, to pass through a fixed point. Velocity (v): depends upon both medium and frequency. Wavelength ( λ ): the linear distance between successive maxima, or minima Chapter 21 - 4 Photons: The Particle Nature of Light Light has both particulate and wavelike properties – Photons with mass. – Photons can be emitted from the source of electromagnetic radiation. λ = ν = ∆ hc h E m/s) 10 x (3.00 light of speed c ) s J 10 62 . 6 ( constant s Planck' frequency wavelength energy 8 34 = ⋅ = = ν = λ = ∆- ξ η Ε Chapter 21 - 5 The Electromagnetic Spectrum Chapter 21 - 6 Refractive Index, n • Note: n = f ( λ ) Typical glasses ca. 1.5 -1.7 Plastics 1.3 -1.6 PbO (Litharge) 2.67 Diamond 2.41 medium) in light of (velocity vacuum) in light of (velocity v c ≡ • Transmitted light distorts electron clouds. • Light is slower in a material vs vacuum. n = refractive index + no transmitted light transmitted light + electron cloud distorts Selected values from Table 21.1, Callister 7e .--Adding large, heavy ions (e.g., lead can decrease the speed of light.--Light can be "bent" Chapter 21 - 7 Total Internal Reflectance φ φ ′ = ′ sin sin n n n ’(low) n (high) n > n ’ 1 φ c φ ' 1 φ angle critical angle refracted angle incident = φ = φ ′ = φ χ ι ι reflected internally is light for 90 when occurs c i i c φ φ ° = φ ′ φ Chapter 21 - 8 Example: Diamond in air • Fiber optic cables are clad in low n material for this reason....
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This note was uploaded on 09/30/2011 for the course PHYSICS 1410 taught by Professor Falco during the Spring '08 term at Texas State.

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2010-04-14 Chapter 21 Optical Properties - Chapter 21 1...

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