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Diffraction and Interference

Diffraction and Interference. Interference Young’s Interference Experiment Diffraction Grating Single-Color Interference Iridescence. Interference. Young’s Interference Experiment.

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Diffraction and Interference

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  1. Diffraction and Interference Interference Young’s Interference Experiment Diffraction Grating Single-Color Interference Iridescence

  2. Interference

  3. Young’s Interference Experiment 1801, Thomas Young discovered that when light of a single color (monochromatic) was directed through two closely spaced pinholes, fringes of brightness and darkness were produced on a screen.

  4. Young’s Interference Experiment • Bright fringes = constructive interference • Waves arrive at the screen in phase • Dark fringes = destructive interference • Waves arrive at the screen out of phase

  5. Diffraction Grating • A series of closely spaced parallel slits or grooves that are used to separate colors of light by interference. • Different colors have different wavelengths and diffract at different rates. • So they constructively interfere at different places.

  6. Single-Color Interference from Thin Films • Interference fringes can be produced by the reflection of light from two surfaces that are very close together. • If you shine a single-color (monochromatic) light onto stacked (with an air wedge) plates of glass, you’ll see dark and bright bands.

  7. Single-Color Interference from Thin Films • The reason for the dark/bright bands is that reflected light from the top plate interferes destructively/constructively with light reflected from the bottom plate.

  8. Single-Color Interference from Thin Films • Practical uses would be to test the precision of lenses. • Straight/round fringes = perfectly flat/round glass • Irregular fringes = irregular surface

  9. Iridescence from Thin Films

  10. Iridescence from Thin Films Iridescence:The phenomenon whereby interference of light waves of mixed frequencies reflected from the top and bottom of thin films produces a spectrum of colors.

  11. Iridescence From Thin Films • A thin film, such as a soap bubble or oil on water, has two closely spaced surfaces. • Light that reflects from one surface may cancel light of a certain frequency that reflects from the other surface. http://webphysics.davidson.edu/physlet_resources/bu_semester2/c26_thinfilm.html

  12. Iridescence From Thin Films • If the film is illuminated with white light and the light that reflects to your eye has blue cancelled due to the reflected light from the other surface, what color will you see?

  13. Iridescence From Thin Films • If the film is illuminated with white light and the light that reflects to your eye has blue cancelled due to the reflected light from the other surface, what color will you see? • The complementary color, yellow!

  14. Iridescence from Thin Films Same principles as Single-Color Interference The shapes of the fringes for both are made by the differences in thickness of the materials. Except we are using light of mixed frequencies and our fringes are made of different colors.

  15. CD 31-1

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