2. Light Emission Chapter 30

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

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

5. Continuous Spectrum Source must be HOT and DENSE

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

7. Absorption Spectrum

8. Types of Spectra Continuous Emission Absorption

9. Rutherford Scattering Experiments Atom He “bullet”

10. Hydrogen Atom u Simplest atom u One proton, one electron u Most abundant atom u 90% of the universe is hydrogen

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

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

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

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

15. Bohr’s Hypotheses u Stable electron orbits exist where the electron does not lose energy.

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

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

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

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

21. +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

22. Emission and Absorption Lines u Lines come from electron transitions u Energy change either comes from (absorption) or is given to (emission) photon. E u Photon energy  Frequency u E = hf u Frequency  1/(Wavelength)  f = c/ u Wavelength means COLOR

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

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

25. Atomic Spectra Review

26. Continuous Radiation u How bright is the continuous spectrum at different colors? u How does a perfect light source emit its light? 400nm 500nm 600nm 700nm

27. Early Experiments Darken inside with carbon black Measure radiation that emerges from hole Blackbody Radiation

28. Vis IR UV

29. Changes with Temperature 7000 K 6000 K 5000 K * * * Visible

30. Blackbody Radiation u Everything in nature emits light u The type of light emitted depends on the temperature of the source u The walls of this room u IR u Stars u Visible and UV u The Corona of the Sun (2,000,000 K) u X-rays

31. Wien’s Displacement Law u The wavelength of the peak of the blackbody curve is inversely proportional to the temperature. Cool stars are red - hot stars are blue max  1/T f max  T

32. Fluorescence UV Photon Visible Photon

33. Phosphorescence UV Photon Visible Photon Let’s wait here

34. LASERS Light Amplification by Stimulated Emission of Radiation Monochromatic: one specific wavelength (color) of light Coherent: every wave is moving in step Directional: beam is tight, strong and concentrated

35. “Pumping”