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Lab 9 Light Beams: Intensity, Absorption, and Scattering

Lab 9 Light Beams: Intensity, Absorption, and Scattering. Objectives. Understanding how preferential scattering of short wavelengths by molecules in the atmosphere leads to.. Blue skies Red sunsets

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Lab 9 Light Beams: Intensity, Absorption, and Scattering

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  1. Lab 9 Light Beams: Intensity, Absorption, and Scattering Objectives • Understanding how preferential scattering of short wavelengths by molecules in the atmosphere leads to.. • Blue skies • Red sunsets • Understand that larger particles, such as cloud droplets, scatter all wavelengths of visible light • Grasp the concepts of exponential decay & growth

  2. White light is the combination of all colors! Credit: NASA

  3. Relevant light processes • Absorption • Scattering • Transmission • Attenuation • gradual loss of radiative energy through some medium (e.g., due to absorption + scattering)

  4. Rayleigh Scattering • When light hits a small particle (e.g., a molecule of air or fat globule in water), it can scatter in all directions • The amount of light scattered is inversely proportional to the wavelength4 • Thus, blues & violets are scattered more than red White Light

  5. Other Scattering Modes • Scattering from larger particles has less preference for wavelength • Tend to scatter all colors (white)

  6. Why is the sky blue? • Rayleigh scattering by molecules Credit: NASA

  7. Why isn’t the sky purple? • Less violet in the spectrum than blue to work with • Human eyes are less sensitive to violet than blue

  8. Why is the sun reddish at sunset? Why are the cloud’s reddish at sunset?

  9. Milk Tank Scattering • We will measure red & blue light scattered out side of tank, as well as both colors exiting tank Less Red Than Blue Red & Blue Milk particles More Red Than Blue

  10. Linear vs. Exponential Growth

  11. Exponential Decay 100 100*0.5 100*0.5*0.5 100*0.53 100*0.54 100*0.55 100 50 25 12.5 6.25 3.125

  12. Light Intensity at Exit 100*0.55= 3.1 4 ml of milk added 100*0.45= 1.0 6 ml of milk added 100*0.35= 0.24 8 ml of milk added

  13. Lab Report • Objectives • Activities (Excel sheet & graph) • Questions • Conclusion • Individual submissions

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