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Light
- 1. Properties of LightProperties of Light
- 2. The Speed of LightThe Speed of Light Galileo’s Experiment A B c = Round Trip Distance/Total Time
- 3. Ole Roemer (1675)Ole Roemer (1675) Earth Jupiter
- 4. Speed of LightSpeed of Light From Roemer’s Experiment c = Diameter of Orbit/Time Delay Modern Value c = 299,792.458 km/sec
- 5. Speed of LightSpeed of Light Absolute constant Nothing travels faster
- 6. Relative VelocitiesRelative 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 = 0 v v v v Vrel = 2v
- 7. Try it with LightTry it with Light Sun ½ c c Intuition says you get ½ c Einstein says c
- 8. Try it with Light Sun½ c c Intuition says you get 1½ c Einstein says c
- 9. Nature of LightNature 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 WavesTypes of Waves Transverse and Longitudinal
- 12. Electromagnetic SpectrumElectromagnetic Spectrum Increasing Wavelength Visible Light
- 13. The Visible SpectrumThe Visible Spectrum 400nm 500nm 600nm 700nm Wavelength means COLOR
- 14. FrequencyFrequency 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 PeriodFrequency and Period Period = 1 Frequency
- 16. Speed, Wavelength, FrequencySpeed, Wavelength, Frequency c = λ f
- 18. Properties of LightProperties of Light Speed (c) Nothing travels faster Absolute constant Wavelength (λ) Gamma rays, X-rays, UV, Visible, IR, Radio In visible wavelength means color Frequency (f) Number of complete waves per second
- 21. Mercury near HorizonMercury near Horizon The atmosphere can act like a prism
- 22. Continuous SpectrumContinuous Spectrum Source must be HOT and DENSE
- 23. Emisson (Bright Line)Emisson (Bright Line) SpectrumSpectrum Source must be HOT and TENUOUS
- 25. Types of SpectraTypes of Spectra Continuous Emission Absorption
- 27. Hydrogen AtomsHydrogen Atoms Simplest atom One proton, one electron Most abundant atom 90% of universe is hydrogen
- 28. Planetary ModelPlanetary Model Force p e- Since electron orbits the proton, a force exists.
- 29. Planetary ModelPlanetary Model p e- Acceleration •Force implies acceleration •Accelerating charges emit light •Light carries energy (E = hf)
- 30. Planetary ModelPlanetary Model p e- Electron moves closer to the nucleus since it requires less energy to be there.
- 31. Planetary ModelPlanetary 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 HypothesesBohr’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 HypothesesBohr’s Hypotheses Transitions can occur between orbits so long as the electron ends up with the energy of the new level.
- 38. +P+P 22 33 44 656 nm 700 nm700 nm400 nm400 nm -e-e HydrogenHydrogen AtomAtom 11 -e-e -e-e 55 -e-e 486 nm 434 nm -e-e 410 nm
- 39. Emission andEmission and Absorption LinesAbsorption 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/λ Wavelength means COLOR
- 40. Hydrogen SpectrumHydrogen Spectrum E n e r g y 1 2 3 4 Lyman (UV) Balmer (VIS) Paschen (IR) Brackett (Far IR)
- 42. Emission & AbsorptionEmission & Absorption Spectra for any ElementSpectra for any Element http://jersey.uoregon.edu/vlab/eleme nts/Elements.html
- 43. ReviewReview
- 44. End of LightEnd of Light
Editor's Notes
- E f E = hf
- Energy of a Photon (E) E = hf