# Diffraction and Interference of Light

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Diffraction and Interference of Light
Chapter 19

19.1 When Light Waves Interfere
Grimaldi found that edges in shadows are not perfectly sharp. Diffraction- bending of waves around a barrier Huygens – all points of a wave front of light could be thought of as new sources of smaller waves. Fig

Young – dev. experiment to explain how light acts as a wave
Produced pattern of light and dark bands, interference fringes Constructive & destructive interference Fig 19 –2 445 Monochromatic- one color –wide central band Coherent waves – waves are in phase.

White light – central band is white, other bands depend on 
Fig Young also measured  of light. Fig  = xd/L x - distance from central to next band, d - distance between slits and L - distance from slit to screen. Ex Prob 448

Single slit – bright central band with dimmer bands on each side
Fig 19-5 & x = L/w x - distance from central to next band, w – width of slit, and L - distance from slit to screen. Fig Prac Pr 451

19.2 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.

Holography – produces a 3-D image that is difficult to copy.

Spectroscope – 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.

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