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Light, Matter and Energy

Light, Matter and Energy. Topics. Review Basic Units and Powers of Ten The Spectrum Light as Waves Light as Particles Atoms Summary. Basic Units. Distance Meter m Mass Kilogram kg Time Second s or sec Energy Joule J (kg m 2 / s 2 ) Power Watt 1 J / s. Powers of Ten.

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Light, Matter and Energy

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  1. Light, Matter and Energy

  2. Topics • Review • Basic Units and Powers of Ten • The Spectrum • Light as Waves • Light as Particles • Atoms • Summary

  3. Basic Units • Distance • Meter m • Mass • Kilogram kg • Time • Second s or sec • Energy • Joule J (kg m2 / s2) • Power • Watt 1 J / s

  4. Powers of Ten

  5. Powers of Ten – II

  6. p.20

  7. White light is a mixture of light of different colors The Spectrum Red Orange Yellow Green Blue Indigo Violet Virtual Physics Lab – Colors Fig. 2-1, p. 22

  8. Light as Waves Virtual Physics Lab – Double Slit Interference

  9. Light as Waves – II p. 23

  10. Speed of Wave = Wavelength x Frequency c = l n c speed of light l wavelength n frequency Example: Tallahassee radio station: 99.9 fm n = 99.9 x 106cycles per second (Hz) c = 3 x 108meters per second (m/s) Therefore, λ = c / n = 3 x 108 / 108= 3 m

  11. The Electromagnetic Spectrum 10-12 m 10-7 m 102 m http://www.chemheritage.org/EducationalServices/FACES/env/readings/photon.htm Virtual Physics Lab - Electromagnetics

  12. - - - - - - - Photoelectric Effect No current flows however Intense the light A current flows only if the light is of sufficiently high frequency http://lectureonline.cl.msu.edu/~mmp/kap28/PhotoEffect/photo.htm

  13. Light as Particles • In 1905, Albert Einstein suggested that light is a huge collection of packets of energy, he called photons • Each photon has energy • h = 6.6261 x 10-34 J . sis Planck’s constant E = h n = h c / l

  14. Atoms

  15. Fraunhofer Lines Dark lines in solar spectrum discovered by Joseph von Fraunhofer (1787 – 1826) Fig. 2-4, p. 24

  16. The Balmer Series of Hydrogen 10 Ångström = 1 nanometer (nm) Balmer Formula (1885) n = 3, 4, … Johann Balmer (1825 – 1898) 1/R = 91.16 nm R is the Rydberg constant Fig. 2-11, p. 28

  17. The Bohr Model of Atoms (1913) Fig. 2-5, p. 26

  18. Atomic Transitions Fig. 2-10, p. 27

  19. Bohr Model of the Hydrogen Atom Ha n = 3 to n = 2

  20. Hb Paschen Ha Lyman Energy Levels of Hydrogen E∞ = 0 eV n = ∞ n = 4 n = 3 n = 2 Balmer E1 = -13.6 eV n = 1

  21. Example: Hydrogen-alpha (Ha) Line • Energy of Photon • E = hc / l = 1240 (eV . nm) / l (nm) • Energy Change (from level n = 3 to n = 2) • E = 13.6 (1/22 – 1/32) = 1.89 eV • Wavelength • 1240 / l = 1.89 • l = 656.5 nm

  22. Neutral Atoms Net charge is zero Fig. 2-13, p. 29

  23. Ionized Atoms Net charge is +1 unit Fig. 2-13, p. 29

  24. Molecule Atom Nucleon n n Nucleus p d u u Quantum Theory of Matter Hydrogen Orbitals

  25. Matter Proton Neutron d u u d u d Photon g Electron Electron Neutrino e ne

  26. Radiation From Space

  27. Spectra: continuous, emission, absorption Fig. 2-7, p. 26

  28. Black Body Radiation Radiation from an object at temperature T A hot object emits a continuous spectrum of colors Wien’s Law T = 3 x 106 / lmax T in Kelvin lmax in meters p. 25

  29. Fig. 2-2, p. 22

  30. Fig. 2-14, p. 30

  31. Doppler Effect Fig. 2-14, p. 30

  32. Fig. 2-15, p. 30

  33. Discovery of Extrasolar Planets Fig. 2-16, p. 31

  34. Summary • Electromagnetic Radiation • Radio, microwaves, light, x-rays, gamma rays differ only in wavelength (and therefore in energy). • Photons • Light behaves like a huge ensemble of particles. • Photons can be emitted, and absorbed, by atoms and molecules. • Atoms and Molecules • Can be identified by their unique emission (or absorption) spectra.

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