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Chapter 29

Chapter 29. Light Waves. Huygens’ Principle. Every point on a wave front can be regarded as a new source of wavelets, which combine to produce the next wave front, whose points are sources of further wavelets, and so on. Plane Waves.

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Chapter 29

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  1. Chapter 29 Light Waves

  2. Huygens’ Principle • Every point on a wave front can be regarded as a new source of wavelets, which combine to produce the next wave front, whose points are sources of further wavelets, and so on. • Plane Waves

  3. Huygen’s Principle can be used to explain the propagation of wave fronts involved in reflection, refraction, and diffraction.

  4. 2. DIFFRACTION • The bending of light that passes around an obstacle or through a narrow slit, causing the light to spread and to produce light and dark fringes. Single Slit Double Slits

  5. Diffraction Notes • Long wavelengths bend a great deal around small objects. • Because of diffraction AM radio waves may be received better than FM radio waves. • Microscopy diffraction limit - One cannot see details of objects that are approximately the same size as or smaller than the wavelength of the illuminating light.

  6. 3. INTERFERENCE • Two point sources • Demo - Finger slit interference • Demo - Single-Color Thin Film Interference

  7. Soap Bubbles

  8. Interference Colors by Reflection from Thin Films • Iridescence - the phenomenon of seeing colors by interference in thin films. • Demo - Soap bubbles and pipe • Example - Coated photographic lenses • Demo - Peacock feathers • Interferometers measure small distances.

  9. 4. POLARIZATION • Common sources of light are not polarized. • Polaroid Crystals - one axis direction absorbs, one transmits. • Polarized glare occurs on reflection from nonmetallic surfaces. • Polarization Demo

  10. COLORS BY TRANSMISSION THROUGH POLARIZING MATERIALS Demo - Polaroids and accessories • Sunglasses

  11. Three-Dimensional Viewing Stereoscopic viewers

  12. Teapot Stereogram

  13. 5. HOLOGRAPHY • Hologram means whole message. • Demo - Reflection hologram • Demo - Transmission hologram • No lenses are used to create nor to view a hologram.

  14. Holography Notes • Object and source both illuminate all of the photographic plate. • The light used to make the hologram must be coherent. • A hologram is an interference pattern.

  15. More Holography Notes • It is best to use coherent light when viewing a hologram. • A hologram can be divided. • One gets a magnified holographic image by viewing a hologram with a longer l of light than was used in creating the hologram.

  16. Chapter 29 Review Questions AM band radio waves travel farther than FM band radio waves because (a) AM waves travel faster than FM waves (b) AM wavelengths are shorter than FM wavelengths (c) AM waves are scattered more than FM waves (d) AM waves are diffracted more than FM waves (d) AM waves are diffracted more than FM waves

  17. If laser light passes by a hair, a pattern of light and dark can be seen on a properly placed screen. What phenomenon (phenomena) is (are) being observed? (a) diffraction (b) polarization (c) chromatic aberration (d) all of the above (e) none of the above (a) diffraction

  18. Polaroid sunglasses worn in a normal viewing position will eliminate polarized glare. (a) vertically (b) horizontally (c) all (b) horizontally

  19. Two polaroids that have their polarization axes at 45o to each other will still allow light to pass through. (a) True (b) False (a) True

  20. The point where a soap bubble bursts will be black just as it bursts. (a) True (b) False (a) True

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