2. Properties of Light

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

4. Ole Roemer (1675) Earth Jupiter

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

6. Speed of Light  Absolute constant  Nothing travels faster

7. 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 V rel = 0 v v vv V rel = 2v

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

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

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

11. Types of Waves  Transverse and Longitudinal Transverse and Longitudinal

12. Wavelength

13. Electromagnetic Spectrum Increasing Wavelength Visible Light

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

15. 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

16. Frequency and Period Period = 1 Frequency

17. Speed, Wavelength, Frequency c = f

18. Photon Energy E  f E = hf

19. 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

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

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

23. Continuous Spectrum Source must be HOT and DENSE

24. Emisson (Bright Line) Spectrum Source must be HOT and TENUOUS

25. Absorption Spectrum

26. Types of Spectra Continuous Emission Absorption

27. Rutherford Scattering Experiments Atom He “bullet”

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

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

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

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

32. 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!!

33. Bohr’s Hypotheses  Stable electron orbits exist where the electron does not lose energy.

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

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

37. Hydrogen EnergyEnergy 2 3 4 5 6563 Å photon Absorption

38. Hydrogen EnergyEnergy 2 3 4 5 6563 Å photon Emission

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

40. Emission and Absorption 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/  Wavelength means COLOR

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

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

43. Emission & Absorption Spectra for any Element  http://jersey.uoregon.edu/vlab/eleme nts/Elements.html

44. Review

45. End of Light