1. Diffraction and Interference of Light
Chapter 19

2. 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

3. 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.

4. 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

5. 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

6. 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.

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

8. 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.