219.1 When Light Waves Interfere Grimaldi found that edges in shadows are not perfectly sharp.Diffraction- bending of waves around a barrierHuygens – all points of a wave front of light could be thought of as new sources of smaller waves. Fig
3Young – dev. experiment to explain how light acts as a wave Produced pattern of light and dark bands, interference fringesConstructive & destructive interference Fig 19 –2 445Monochromatic- one color –wide central bandCoherent waves – waves are in phase.
4White light – central band is white, other bands depend on FigYoung also measured of light.Fig = xd/Lx - distance from central to next band, d - distance between slits and L - distance from slit to screen.Ex Prob 448
5Single slit – bright central band with dimmer bands on each side Fig 19-5 &x = L/wx - distance from central to next band, w – width of slit, and L - distance from slit to screen.Fig Prac Pr 451
619.2 Applications of Diffraction Colors on butterfly wings and beetles are produced by diffraction.Diffraction grating – transmits or reflects light & forms an interference pattern like double slit.
7Holography – produces a 3-D image that is difficult to copy.
8Spectroscope – used to measure Fig & Fig = xd/L = d sin Diffraction limits the ability of a lens to distinguish two closely spaced objects.Rayleigh criterion – if central band of one star falls on central band of the other can be resolved.Can be reduced by increasing size of lens.