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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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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!
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)
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)
Speed of Light • Speed in Vacuum • 300,000 km/sec • 186,000 mi/sec • Speed in Other Materials • Slower in Air, Water, Glass
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
The Visible Spectrum A range of light waves extending in wavelength from about 400 to 700 nanometers.
Francesco Grimaldi (1618-1663), Italian mathematician, physicist, and artist, first noticed interference fringes looking at the shadow of an opaque object. LNK2LRN
How light Diffracts and Interferes with itself as it passes through 2 narrow openings. LNK2LRN
Thomas Young demonstrated diffraction and interference of light in 1802. Is this an example of chromatic aberration? LNK2LRN And remember, “Blue bends best!”
How to derive the equation for λ , the wavelength of light. x λ λ = x·d / L or λ = d·sinθn/ n LNK2LRN
Correlation of spectrum color with wavelength (nanometers). ColorWavelength (nm) Violet410-440 Blue440-490 Green490-540 Yellow540-600 Orange600-630 Red630-770
X-ray diffraction allows us to see the molecular lattice in a crystal. LNK2LRN
THE END. Next Topic: Electric Forces and Fields.