1. Properties of Light

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

3. Ole Roemer (1675)
Jupiter
Earth

4. Speed of Light From Roemer’s Experiment Modern Value
c = Diameter of Orbit/Time Delay
Modern Value
c = 299, 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 c
½ c
Intuition says you get ½ c
Einstein says c

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

9. Nature of Light Particle? Wave? Newton
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. The Visible Spectrum
400nm nm nm nm
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. Frequency and Period
Period = 1
Frequency

16. Speed, Wavelength, Frequency
c =  f

17. Photon Energy
E  f
E = hf

18. Properties of Light Speed (c) Nothing travels faster Wavelength ()
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. Basic Spectrograph Collimating Lens Imaging Lens Dispersive Element
Slit
Dispersive Element
Imaging Lens
Recording Device

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

22. Source must be HOT and DENSE
Continuous Spectrum
Source must be HOT and DENSE

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

24. Absorption Spectrum

25. Types of Spectra
Continuous
Emission
Absorption

26. Rutherford Scattering Experiments
Atom
He “bullet”

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

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

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

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

31. Planetary Model Atoms do not exist!!
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. Hydrogen
Absorption
Energy 2 3 4 5
6563 Å photon

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

38. Hydrogen Atom 434 nm 656 nm 486 nm 410 nm -e -e -e -e -e 400 nm 700 nm2
656 nm -e 1 -e +P
486 nm
410 nm -e -e
400 nm
700 nm

39. 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/l
Wavelength means COLOR

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

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

42. Emission & Absorption Spectra for any Element

43. Review

44. End of Light