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Properties of Light

Properties of Light. A. B. The Speed of Light. Galileo’s Experiment. c = Round Trip Distance/Total Time. Jupiter. Earth. Ole Roemer (1675). Speed of Light. From Roemer’s Experiment c = Diameter of Orbit/Time Delay Modern Value c = 299,792.458 km/sec. Speed of Light.

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Properties of Light

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  1. Properties of Light

  2. A B The Speed of Light Galileo’s Experiment c = Round Trip Distance/Total Time

  3. Jupiter Earth Ole Roemer (1675)

  4. Speed of Light • From Roemer’s Experiment • c = Diameter of Orbit/Time Delay • Modern Value • c = 299,792.458 km/sec

  5. Speed of Light • Absolute constant • Nothing travels faster

  6. Relative Velocities • Our physical sense of velocities is relative • How we measure speed depends on how we are moving and how the object we are measuring in moving Vrel = 2v v v v Vrel = 0 v

  7. Try it with Light Sun ½ c c Intuition says you get ½ c Einstein says c

  8. Try it with Light Sun ½ c c Intuition says you get 1½ c Einstein says c

  9. Nature of Light • Particle? • Newton • Wave? • Christian Huygens in Newton’s day • Thomas Young (1801) • Light can diffract - must be a wave • Transverse wave

  10. Types of Waves • Transverse and Longitudinal

  11. Wavelength

  12. Electromagnetic Spectrum Increasing Wavelength Visible Light

  13. 400nm 500nm 600nm 700nm The Visible Spectrum Wavelength means COLOR

  14. Frequency • Number of complete events occurring in a period of time • Waves/second • Examples • Second hand on a clock? • 1 cycle/minute = 1/60 cycle/sec • US Presidential Electons • 1 election/4 years = 1/4 election/year

  15. 1 Period = Frequency Frequency and Period

  16. Speed, Wavelength, Frequency c =  f

  17. Photon Energy E  f E = hf

  18. Properties of Light Speed (c) Nothing travels faster Absolute constant Wavelength () Gamma rays, X-rays, UV, Visible, IR, Radio In visible wavelength means color Frequency (f) Number of complete waves per second Energy of a Photon (E) E = hf

  19. Collimating Lens Imaging Lens Dispersive Element Slit Recording Device Basic Spectrograph

  20. Mercury near Horizon The atmosphere can act like a prism

  21. Continuous Spectrum Source must be HOT and DENSE

  22. Emisson (Bright Line) Spectrum Source must beHOTandTENUOUS

  23. Absorption Spectrum

  24. Continuous Emission Absorption Types of Spectra

  25. He “bullet” Atom Rutherford Scattering Experiments

  26. Hydrogen Atoms • Simplest atom • One proton, one electron • Most abundant atom • 90% of universe is hydrogen

  27. e- Force p Planetary Model Since electron orbits the proton, a force exists.

  28. e- Acceleration p Planetary Model • Force implies acceleration • Accelerating charges emit light • Light carries energy (E = hf)

  29. e- p Planetary Model Electron moves closer to the nucleus since it requires less energy to be there.

  30. Planetary Model • But the electron is still accelerating • Must still be radiating energy (light) • Must move still closer to the nucleus • Electron will spiral into and collide with the nucleus (in about 10-8 seconds) Atoms do not exist!!

  31. Bohr’s Hypotheses • Stable electron orbits exist where the electron does not lose energy.

  32. Electrons can be here or here but not here p

  33. Bohr’s Hypotheses • Transitions can occur between orbits so long as the electron ends up with the energy of the new level.

  34. 5 4 3 Energy 6563 Å photon 2 Hydrogen Absorption

  35. 5 4 Energy 3 6563 Å photon 2 Hydrogen Emission

  36. Hydrogen Atom 5 4 -e 434 nm 3 2 656 nm -e 1 -e +P 486 nm 410 nm -e -e 400 nm 700 nm

  37. Emission andAbsorption Lines • Lines come from electron transitions • Energy change either comes from (absorption) or is given to (emission) photon. E • Photon energy  Frequency • E = hf • Frequency  1/(Wavelength) • f = c/l • Wavelength means COLOR

  38. Brackett (Far IR) Paschen (IR) 4 3 Balmer (VIS) 2 1 Lyman (UV) Hydrogen Spectrum Energy

  39. Aluminum Argon Calcium Carbon Helium Hydrogen Iron Krypton Magnesium Neon Nitrogen Oxygen Sodium Sulfur Xenon

  40. Emission & Absorption Spectra for any Element • http://jersey.uoregon.edu/vlab/elements/Elements.html

  41. Review

  42. End of Light

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