3.3.2 Refraction, diffraction, and interference

3.3.2 Refraction, diffraction, and interference

1. Interference

   • path difference - the difference in distances from two coherent sources to an interference fringe
     • coherent - two sources of waves emit waves with a constant phase difference
   • Young's experiment
   • white light
     • interference pattern - colours split
       • blue closest to centre

2. Diffraction

   • single slit
     • central fringe is twice as wide as each of the outer fringes
   • know derivation
   • Applications
     • spectrometer
       • study spectrum of light from any light source and to measure light wavelengths very accurately
     • X-ray crystallography
       • wavelength is of similar scale to spacing between atoms in crystalline solids

3. Refraction at a plane surface

   • refractive index, n = C / Cs
     • n of air ~ 1
   • Snell's law of refraction for a boundary
     • n1sinθ1 = n2sinθ2
   • Total internal reflection
     • θc = n2 / n1
   • structure of fibre optics
     • dispersion
       • modal - rays take longer path
       • material - different wavelengths travel at different speeds

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