31 outline particles waves and light propagation and

31 outline • • • particles, waves, and light propagation and scattering of light reflection and refraction dispersion polarization 1

Light • can behave as wave or particle 2

Interference is evidence of the wave nature of light 3

Photoelectric Effect Light stimulates emission of electrons from metal. Kmax independent of light intensity explained by ‘photon’ concept of light. 4

Light Photon • Smallest ‘bundle’ of electromagnetic field • Carries energy and momentum 5

continuous hydrogen helium barium mercury 6

Electron energy transitions leading to Line Spectra Example: 7

elastic scattering Stokes Raman scattering Anti-Stokes Raman scattering Resonance absorption spontaneous emission Photoelectric effect stimulated emission Compton scattering 8

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Huygen’s Principle • each part of a wave at some instant is a ‘source’ point of waves • the wave at a later instant is the tangential envelope of the point-sources 12

Fermat’s Principle Light speed in materials is v = c/n. In glass v is about c/1. 5 A B 13

Actual light path from A to B is the path which takes the least time. 14

Law of Reflection 15

Snell’s Law 16

Use Snell’s Law to find the angle of refraction. 17

Light reflects and refracts at material boundaries. 18

Total Internal Reflection 19

Calculate critical angle if index of water is 1. 33. 20

Mirages • index of refraction of air depends on density of air 21

Light Dispersion • Color separation in material with wavelength dependent index of refraction 22

Polarization of light by reflection 23

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