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How is Light Produced?

How is Light Produced?. It ’ s all tied to energy Energy of the material ’ s temperature Energy levels within atoms. Motivation. If we understand how light is produced, then when we see light we ’ ll know the conditions under which it was created. Examples: That scope thing Spock uses

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How is Light Produced?

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  1. How is Light Produced? • It’s all tied to energy • Energy of the material’s temperature • Energy levels within atoms

  2. Motivation • If we understand how light is produced, then when we see light we’ll know the conditions under which it was created. • Examples: • That scope thing Spock uses • Atmospheric composition of a newly discovered planet • Can a given star support life?

  3. Kirchoff’s Laws - 3 types of spectra • Continuous or Continuum • Ex: Blackbody radiation • Emission • Absorption

  4. Hot solid thing Transparent thing blocking other hot thing Hot gaseous thing

  5. Hot dense thing

  6. Continuous Spectrum • Continuous, continuum • All colors • Examples: stars are nearly blackbody, incandescent light bulbs, electric burners, people, etc.

  7. Causes of Continuum • Blackbody • Thermal • Hot dense material • Bremsstrahlung / Free-free • An electron passes by a proton / nucleus • Recombination / Free-bound • Electron captured by a proton / nucleus • Compton Scattering • Existing photon has its wavelength changed by a collision

  8. http://www.oswego.edu/~kanbur/a100/images/planck.jpg (Assuming stars are same size.)

  9. Planck’s Law • Completely describes the light (blackbody radiation) coming from an object.

  10. Stefan-Boltzmann Law • L=σT4×star’s surface area • The total brightness of an object (at all colors added together) depends on the Temperature to the 4th power (and size of the object). • Temperature makes objects glow. The hotter it is, the more it glows.

  11. http://www.oswego.edu/~kanbur/a100/images/planck.jpg (Assuming stars are same size.)

  12. Wein’s Law • λmax=2,900,000/T (in nm) • What color an object is brightest at depends on the Temperature of the object. • Hotter objects are brightest in blue/purple (and ultraviolet). • Cooler objects are brightest in red (and infrared).

  13. http://hypertextbook.com/physics/modern/planck/ Our Sun looks yellow Hottest stars look blue (Assuming same size stars.) Cool stars look red

  14. How can you tell which object is hotter/larger • Color of the peak tells us the object’s temperature. • If two objects have the same color, the brighter one is physically larger. • If two objects of the same size, the hotter one will be brighter at all colors.

  15. Hot gaseous thing

  16. Emission Spectrum • Hot thin gas • Only a few select colors • Examples: some fluorescent lights, neon lights, natural gas flames, warm gas clouds in space

  17. http://astronomy.nmsu.edu/nicole/teaching/ASTR110/lectures/lecture19/pics/emission_spectra.gifhttp://astronomy.nmsu.edu/nicole/teaching/ASTR110/lectures/lecture19/pics/emission_spectra.gif

  18. http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.pnghttp://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png When an electron goes down an orbital

  19. http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.pnghttp://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png A photon comes out of a specific color

  20. Absorption Spectrum • Hot dense object blocked by cool thin gas • Continuum minus emission • All colors except a select few • Examples: nearby gas cloud blocks a farther star, nearer galaxy blocks a far quasar, sunglasses block sunlight, Earth’s atmosphere blocks sunlight

  21. Transparent thing blocking other hot thing

  22. http://www.solarobserving.com/pics/hydrogen-spectra.jpg

  23. Absorption and emission spectra are opposite in appearance and cause.

  24. Emission spectrum Electrons go down levels on their own and put out light as a result.

  25. http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.pnghttp://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png When an electron goes down an orbital

  26. http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.pnghttp://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png A photon comes out of a specific color

  27. Absorption Spectrum Light of all colors comes in. When the color is just right, it makes the electron pop up to a higher level.

  28. http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.pnghttp://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png Light of all colors comes in

  29. http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.pnghttp://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png Only the right color of light is used up to make the electron jump up orbitals

  30. http://www.physics.umd.edu/courses/Phys401/bedaque06/discrete_spectra.jpghttp://www.physics.umd.edu/courses/Phys401/bedaque06/discrete_spectra.jpg bright emission lines become dark absorption lines

  31. Conclusion • Colors of light (how many colors and how bright) call tell us the temperature, density, composition, and even shape of an object.

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