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Light and Atoms

Light and Atoms. Part I. Light. Importance light is the only way of getting information most experiments cannot be setup on Earth. Background. Electricity force between electrical charges Magnetism force between magnetic poles Electricity and Magnetism are related

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Light and Atoms

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  1. Light and Atoms Part I

  2. Light • Importance • light is the only way of getting information • most experiments cannot be setup on Earth

  3. Background • Electricity • force between electrical charges • Magnetism • force between magnetic poles • Electricity and Magnetism are related • one can produce the other • class demos

  4. What is Light? • Electromagnetic Wave • wavelength (l) • distance between crests • frequency (f) • number of crests/second • speed • v = lf • same for all wavelengths • same for all frequencies

  5. What is Light? • Color • related to wavelength • longer l - redder • shorter l - bluer • visible light • white light • all colors

  6. What is Light? • The Electromagnetic Spectrum • Visible light small portion of spectrum • longest l • radio waves • shortest l • gamma rays • The Spectrum • radio waves, infrared, visible light, ultraviolet, x-rays, gamma rays

  7. Electromagnetic Spectrum

  8. What is Light? • Carries Energy • shorter wavelengths - more energy • longer wavelengths - less energy • Intensity • energy per time per area • inverse square law

  9. Wien’s Law • Blackbody • perfect absorber of energy • energy radiated depends on temp • Color related to temperature • peak l depends on temp

  10. Types of Spectra • Continuous • High density hot gas, liquid, or solid • blackbody would give this type • continuous rainbow • Light at all wavelengths

  11. Types of Spectra • Emission Spectra • Hot low density gas • Light only at some wavelengths • pattern of bright lines • Absorption Spectra • Cool gas between observer and light source • Light missing or dimmer at some wavelengths • continuous spectra with dark lines

  12. Atoms • Structure of Atoms • nucleus • number of protons in nucleus determines kind of element • orbiting electrons • classical problem

  13. Electrons and Spectra • only certain orbits allowed • each orbit has certain energy • electrons jump between allowed orbits • down to lower orbit • releases energy • emits light • emission spectra • up to higher orbit • absorbs energy • absorbs light • absorption spectra

  14. Electrons and Spectra • electron orbits are unique • Elements have own distinct spectra • Elements can be identified

  15. The Doppler Shift • Motion causes shift in wavelength • size of shift proportional to speed • source moving away • shifted to longer wavelengths - redshift • source approaching • shifted to shorter wavelengths - blueshift

  16. The Doppler Shift • observer approaching source • shifted to shorter wavelengths - blueshift • observer moving away from source • shifted to longer wavelengths -redshift • If source and observer are approaching • wavelengths decrease • If source and observer are moving farther apart • wavelengths increase

  17. Atmospheric Effects • Earth"s atmosphere absorbs some l • visible light not absorbed • IR, UV, X-ray, & gamma absorbed • Atmospheric window • wavelengths that can pass through atmosphere

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