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Dive into the 200-year debate on whether light is made of particles or waves, settled in the early 1900s with key figures, speed of light, electromagnetic spectrum, visible spectrum, diffraction, interference, and X-ray diffraction. Explore the relationship between spectrum color and wavelength, crystal lattice, and more.

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  1. This Presentation is Brought to You by Interference and Diffraction.

  2. Light - what is it? Particles or Waves? • 200 year debate started in 1700’s. • Supposedly settled in 1802. • Finally resolved in early 1900’s. Before the 1700’s!

  3. The Particle Theorists Pierre Simon Laplace (1749-1827) Sir Isaac Newton (1642-1727) Support later provided by: Jean-Baptiste Biot (1774-1862) Sir David Brewster (1781-1868)

  4. The Wave Theorists Rene DesCartesChristian Huygens Robert Hooke (1596-1650) (1629-1695) (1635-1703) Support later provided by: Thomas Young (1773-1829) Max Planck (1858-1947)

  5. Speed of Light • Speed in Vacuum • 300,000 km/sec • 186,000 mi/sec • Speed in Other Materials • Slower in Air, Water, Glass

  6. The Electromagnetic SpectrumA range of light waves extending in wavelength from radio waves to gamma rays. • Radio Waves - communication • Microwaves - used to cook • Infrared - heat • Visible Light - detected by your eyes • Ultraviolet - causes sunburn • X-rays - penetrates tissue • Gamma Rays - most energetic

  7. The Visible Spectrum A range of light waves extending in wavelength from about 400 to 700 nanometers.

  8. Electromagnetic Spectrum

  9. Francesco Grimaldi (1618-1663), Italian mathematician, physicist, and artist, first noticed interference fringes looking at the shadow of an opaque object. LNK2LRN

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  11. How light Diffracts and Interferes with itself as it passes through 2 narrow openings. LNK2LRN

  12. Thomas Young demonstrated diffraction and interference of light in 1802. Is this an example of chromatic aberration? LNK2LRN And remember, “Blue bends best!”

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  14. How to derive the equation for λ , the wavelength of light. x λ λ = x·d / L or λ = d·sinθn/ n LNK2LRN

  15. Correlation of spectrum color with wavelength (nanometers). ColorWavelength (nm) Violet410-440 Blue440-490 Green490-540 Yellow540-600 Orange600-630 Red630-770

  16. X-ray diffraction allows us to see the molecular lattice in a crystal. LNK2LRN

  17. The arrangement of atoms in a crystal. LNK2LRN

  18. THE END. Next Topic: Electric Forces and Fields.

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