Properties of Light

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

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

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

22. Continuous Spectrum Source must be HOT and DENSE

23. Emisson (Bright Line) Spectrum Source must beHOTandTENUOUS

24. Absorption Spectrum

25. Continuous Emission Absorption Types of Spectra

26. He “bullet” Atom Rutherford Scattering Experiments

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

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

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

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

31. 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!!

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

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

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

36. 5 4 3 Energy 6563 Å photon 2 Hydrogen Absorption

37. 5 4 Energy 3 6563 Å photon 2 Hydrogen Emission

38. 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

39. 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

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

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

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

43. Review

44. End of Light