1. Chapter 29 Light Waves

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

3. ....... Consider several points on the wave front to be sources of secondary wavelets........

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.  Demo - Laser, diffraction accessories, and rainbow disks

6.   If the wavelength of water waves are small compared to the size of an ocean vessel, the vessel will cast a “shadow.”   For the same waves a stick will not cast a “shadow.”

7.   Long wavelengths bend a great deal around small objects.   Because of diffraction AM radio waves travel farther 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.

8. 3.INTERFERENCE  Slide - Interference Transparencies Slide  Demo - Finger slit interference  Demo - Single-color thin film interference  Demo - Optical flats and sodium lamp  Demo - Newton's rings and phase reversal

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

10. Thin Film t Air Phase Reversal upon reflection Path Difference = 2t = n for destructive interference Thus t = n( /2) n = 1,2,3,4,…… You see the complement of whichever color is destructively interfered with.

11. 4.POLARIZATION  Polarization Diagram  Video - Polarization Diagram  Crossed Polaroids  Video - Crossed Polaroids  Demo - Polaroids   Light waves are transverse. This is verified by polarization.

12.   Common sources of light are not polarized.   Polaroid Crystals - one axis direction absorbs, one transmits.   Polarized glare occurs on reflection from nonmetallic surfaces.

13. COLORS BY TRANSMISSION THROUGH POLARIZING MATERIALS  Video - Crossed Polaroids and Crystal  Video - Polarizers and Stress  Demo - Polaroids and accessories

14. Three-Dimensional Viewing   Stereoscopic viewers  Slide  Slide - Stereogram Slide

15. 5.HOLOGRAPHY   Hologram means whole message.  Demo - Reflection hologram  Demo - Transmission hologram   No lenses are used for imaging in the creation or the viewing of a hologram.

16.  both illuminate  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.

17.  viewing  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 of light than was used in creating the hologram.

18. Chapter 29 Review Questions

19. 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

20. 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

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

22. Red is bent the most when it travels through a (a) light pipe (optical fiber) (b) prism (c) grating

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

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

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