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Lecture 6 Light and matter Harris Ch.18.
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Light striking a sample can be 1. reflected 2. transmitted 3. absorbed 4. scattered
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Reflected light Incident light Emergent light P0P0 P1P1 Absorbed light Scattered light
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Refractive index
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Air Glass Longer wavelength Shorter wavelength Snell’s law
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Reflected light P r Incident lightEmergent light P0P0
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Incident lightEmergent light Transparent plate P0P0 P1P1
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Air 1 Quarz 1.5 Water 1.33 T=0.85 R=0.04 Air-quarz Water-quarz R=0.003 T=0.92 emptyWith water
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Absorbing plate
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Incident light Emergent light Absorbing plate P0P0 P1P1 0 l dx dP P dP= N P N=C Volume Volume= 1 dx N = C dx
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Incident light Emergent light Absorbing plate P0P0 P1P1 0 l dx dP P
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Incident light Emergent light Absorbing plate P0P0 P1P1 0 l dx dP P absorbance Sensitivity is the same for any power (P)
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Beer’s law Bugert, Lambert and Beer A concentration Straight line!
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When photon is absorbed, the system jumps to the next energy level
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Luminescence A photon is absorbed and then re-emitted at different wavelength
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Incident light P0P0 Emergent light P1P1 Re-emitted light Absorbed light
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If absorbance is small:
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Incident light P0P0 Emergent light P1P1 Re-emitted light Absorbed light sensetivity is proportional to the source power
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Limits to Beer’s Law Polychromatic light (several wavelength)
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Limits to Beer’s Law Incident light P0P0 Emergent light P1P1 Stray light
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