Diffraction and Interference of Light

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 19-1 444

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 19-3 445
• Young also measured ? of light.
• Fig 19-4 447
• ? 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 6 449
• x ?L/w
• x - distance from central to next band, w width
  of slit, and L - distance from slit to screen.
• Fig 19-7 450 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.
• P 453

8

• Spectroscope used to measure ?
• Fig 19-9 454 Fig 19-10 455
• ? 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.