HONR228Q Notes section h:

  • Applications of Atomic and Molecular Physics

    1. Spectral identification of materials

      1. Medical applications
        1. Identification of drugs in blood or urine
        2. Life-saving when applied to unconscious drug overdose victim
      2. Carcinogens in food identified in trace quantities
        1. "Delaney clause" in 1958 FDA regulation
        2. Carcinogens in food, water, etc. identified in trace quantities
        3. Outdated by spectral identification (Delaney clause removed)
      3. Identifying extremely small quantities of impurities: ~1:109

    2. Fluorescence and Phosphorescence

      1. Fluorescence
        1. DEMO P3-23: CATHODE-RAY TUBE - FLUORESCENCE EFFECT
          1. Demonstrates fluorescence with electrons and x-rays or gamma-rays
        2. DEMO P3-61: FLUORESCENT LIQUIDS
        3. DEMO P3-62: FLUORESCENT CHALK
          1. Fluorescence with UV photons
          2. Photon or electron raises level of outer atomic electron or
          3. Photon or electron raises molecular vibrational or rotational level
          4. Electron falls back into lowest orbital, emitting characteristic frequency/color or
          5. Molecular vibrational or rotational leevel relaxes back to its lowest level, emitting characteristic radiation
        4. Wavelength Shifter Bar
          1. DEMO P3-63: WAVELENGTH SHIFTER BAR
          2. Plastic with fluorescein dye
          3. Photons more energetic than green (blue, violet, UV) absorbed
          4. Electron emitted, then falls back to ground state, emitting green photon
          5. Less energetic photons retain their own color
          6. Fluorescein used as UV detector
        5. Fluorescence used in soap
          1. P3-67: FLUORESCENCE OF LAUNDRY SOAP
          2. Soap makes water "wetter" by creating ions
          3. Surface tension reduced so it can flow into crevices in fabric
          4. Fluorescent chemical part of soap residue
          5. UV in normal light causes extra "brightness"
          6. Illuminate with black light (UV) to see extent of fluorescent residue
      2. Phosphorescence
        1. DEMO P3-64: PHOSPHORESCENCE - BLACK LIGHT AND OSCILLOSCOPE
          1. Delayed fluorescence, may last several seconds or longer
          2. Examples: oscilloscope, TV, computer screen

    3. Related luminescence phenomena

      1. Resonance fluorescence
        1. DEMO P3-52: RESONANCE RADIATION
        2. White light shines onto iodine vapor in glass flask
        3. Characteristic magenta color of iodine is absorbed and re-emitted in all directions by iodine gas
        4. Yellow (complementary color) passes through
      2. Resonance absorption
        1. DEMO N2-32: ABSORPTION SPECTRA OF GLASS
        2. Colored glass tints caused by resonance absorption of molecular spectral lines from dye in glass
        3. Glass shows complementary comor to color of radiation absorbed
        4. Examples include absorption of UV by the ozone layer
      3. Thermoluminescence
        1. Used for dating materials approximately 2000 years old
        2. Quartz-based pottery shards have "metastable" atomic states
        3. Metasable states easily induced to return to ground state by heating, and emit photons
        4. Electrons raised into metastable states by cosmic radiation
        5. Exposure to cosmic radiation per year known
        6. When sample heated it emits light photons proportional to cosmic ray exposure
        7. Data used to determine age of sample
      4. Triboluminescence
        1. DEMO P3-65: WINTERGREEN MINTS
        2. UV created by charge separation when material broken up
        3. UV creates fluorescence when absorbed by chemical in mint
        4. Basic description of triboluminescence
        5. Linda M. Sweeting (Towson University, Maryland: SCIENTIFIC EXPERIMENTS AT HOME: WINTERGREEN CANDY AND OTHER TRIBOLUMINESCENT MATERIALS

    4. The laser

      1. LASER acronym for "Light Amplification by the Stimulated Emission of Radiation"
      2. Example: Helium-Neon laser
        1. Red light is transition in neon (color of neon discharge tube)
        2. Stimulated emission enhances intensity - optical pumping
        3. Standing waves form between two mirrors at ends of tube
        4. Approximately 5% of light hitting mirror leaves LASER (95% silvered)
          1. DEMO L2-22: INFINITY MIRROR
          2. Half-silvered mirror; deduce dynamic range of the eye ~220
          3. DEMO L2-23: MIRROR BOX
          4. Example of half-silvered mirror
        5. DEMO: P3-71: VISIBLE LASER
          1. Use hand-held gratings to see spectrum of laser light
          2. Inside of laser full spectra of helium and neon are visible
          3. Outside of laser only single wavelength is visible

    5. The microwave oven

      1. DEMO K8-51: MICROWAVE OVEN
      2. ~12cm wavelength microwaves absorbed by water molecules
      3. Electromagnetic wave energy converted to heat
        1. Water is polar molecule - permanent dipole moment
        2. DEMO J4-12: ELECTROSTATIC FORCE - MOVING LUMBER
        3. Microwave radiation causes water molecule to invert dipole orientation
        4. Applet showing how water molecule moves under the influence of an electric field.
        5. Motion of water molecule imparts kinetic energy to adjacent molecules
        6. Motion of molecules is kinetic energy or heat given to food being cooked
      4. 3D standing waves cause hot and cold spots
        1. DEMO G4-22: CHLADNI FIGURES - OSCILLATOR DRIVEN
          1. Type of standing wave in microwave oven
        2. SLIDES ILLUSTRATING HOT/COLD PATTERN IN MICROWAVE OVEN
      5. Why doesn't the microwave energy escape and cook you?
        1. DEMO J3-21: FARADAY CAGE
        2. DEMO J3-23: FARADAY CAGE - RADIOWAVES
        3. Microwaves cannot escape oven if holes are smaller than the wavelength of the microwaves
      6. Superheated water from a microwave oven exploding.
      7. Danger and fun with microwave ovens web references.

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