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PHYS 221 Recitation

PHYS 221 Recitation. Kevin Ralphs Week 11. Overview. HW Questions Diffraction Interference. Diffraction. What does it tell me? How a wave behaves near objects Only an appreciable affect when the length scale of the wave and the geometry are similar Visible light: 400nm – 700nm

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PHYS 221 Recitation

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  1. PHYS 221 Recitation Kevin Ralphs Week 11

  2. Overview • HW Questions • Diffraction • Interference

  3. Diffraction • What does it tell me? • How a wave behaves near objects • Only an appreciable affect when the length scale of the wave and the geometry are similar • Visible light: 400nm – 700nm • Sound waves: 17mm – 17m

  4. Interference • What does it tell me? • How waves mix together • Always occurs, but is appreciable only when the waves are coherent • Based on the principal of superposition • Waves add together directly… intensities don’t if the light is coherent! • The square root of intensities for coherent light will

  5. Interference • There are two main sources of interference that we will consider • Path length difference • Reflected waves can pick up a phase shift when going into a medium with a higher index of refraction

  6. Interference • Constructive Interference • Occurs when the phase difference is an integer multiple of 2π or the path length difference is an integer multiple of the wavelength • Destructive Interference • Occurs when the phase difference is an odd integer multiple of πor the path length difference is a half-integer multiple of the wavelength • As you can see, there are multiple solutions to any interference problem (an infinite number actually). The index m helps you to differentiate between them

  7. Main Strategy • For any kind of diffraction or interference problem, the game is always about counting up possible sources of interference and setting that equal to the interference condition you want

  8. Topics • Double Slit Interference • Single Slit Diffraction • Diffraction Gratings • Optical Resolution and Rayleigh Criterion

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