Light

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Light

  1. 1. What is Light?
  2. 2. Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s trough crest
  3. 3. Wavelength (length/cycle) Wavelength (  ): the length of one complete cycle trough crest Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s
  4. 4. Wavelength (length/cycle) Amplitude : 1/2 height between trough and crest Amplitude trough crest Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s
  5. 5. Wave Speed = wavelength x frequency Wave Speed =  f (length/second) = (length/cycle) x (cycle/second)
  6. 6. Light as a Wave Light waves are characterized by a wavelength  and a frequency f c = 300,000 km/s = 3  10 8 m/s l
  7. 7. Electromagnetic Waves
  8. 8. Light as a Wave Wavelengths of light are measured in units of nanometers (nm) or Å ngstr öm (Å) : 1 nm = 10 -9 m 1 Å = 10 -10 m = 0.1 nm Visible light has wavelengths between 4000 Å and 7000 Å (400 nm – 700 nm) .
  9. 9. The Electromagnetic Spectrum Need satellites to observe Wavelength Frequency High flying air planes or satellites
  10. 10. Wavelengths and Colors D i f f e r e n t colors of visible light correspond to different wavelengths.
  11. 11. Visible Light (VIS) 700 to 400 nm Our eyes are sensitive to this region of the spectrum Red - Orange - Yellow - Green - Blue - Indigo - Violet
  12. 12. Solar Radiation The Source for 99.9% of Earth’s Energy
  13. 13. Solar Spectrum The sun emits radiation at all wavelengths Most of its energy is in the IR - VIS - UV portions of the spectrum ~50% of the energy is in the visible region ~40% in the near-IR ~10% in the UV Wavelength (m)
  14. 14. RADIO WAVES <ul><li>Have the longest wavelengths and lowest frequencies of all the electromagnetic waves. </li></ul><ul><li>A radio picks up radio waves through an antenna and converts it to sound waves. </li></ul><ul><li>Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency. MRI (MAGNETIC RESONACE IMAGING) </li></ul><ul><ul><li>Uses radio waves with a magnet to create an image </li></ul></ul>
  15. 15. MICROWAVES <ul><li>Microwaves —have the shortest wavelengths and the highest frequency of the radio waves. </li></ul><ul><ul><li>Used in microwave ovens. </li></ul></ul><ul><ul><ul><li>Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food. </li></ul></ul></ul><ul><ul><li>Used by cell phones and pagers. </li></ul></ul><ul><ul><li>RADAR ( Ra dio D etection a nd R anging) </li></ul></ul><ul><ul><ul><li>Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return. </li></ul></ul></ul>
  16. 16. INFRARED RAYS <ul><li>Infrared = below red </li></ul><ul><li>Shorter wavelength and higher frequency than microwaves. </li></ul><ul><li>You can feel the longest ones as warmth on your skin </li></ul><ul><li>Heat lamps give off infrared waves. </li></ul><ul><li>Warm objects give off more heat energy than cool objects. </li></ul><ul><li>Thermogram —a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off. Therefore people give off infrared rays. </li></ul>
  17. 17. VISIBLE LIGHT <ul><li>Shorter wavelength and higher frequency than infrared rays. </li></ul><ul><li>Electromagnetic waves we can see. </li></ul><ul><li>Longest wavelength= red light </li></ul><ul><li>Shortest wavelength= violet (purple) light </li></ul><ul><li>When light enters a new medium it bends (refracts). Each wavelength bends a different amount allowing white light to separate into it’s various colors ROYGBIV. </li></ul>
  18. 18. ULTRAVIOLET RAYS <ul><li>Shorter wavelength and higher frequency than visible light </li></ul><ul><li>Carry more energy than visible light </li></ul><ul><li>Used to kill bacteria. (Sterilization of equipment) </li></ul><ul><li>Causes your skin to produce vitamin D (good for teeth and bones) </li></ul><ul><li>Too much can cause skin cancer. </li></ul><ul><li>Use sun block to protect against (UV rays) </li></ul>
  19. 19. X- RAYS <ul><li>Shorter wavelength and higher frequency than UV-rays </li></ul><ul><li>Carry a great amount of energy </li></ul><ul><li>Can penetrate most matter. </li></ul><ul><li>Bones and teeth absorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed) </li></ul><ul><li>Too much exposure can cause cancer </li></ul><ul><ul><li>(lead vest at dentist protects organs from unnecessary exposure) </li></ul></ul><ul><li>Used by engineers to check for tiny cracks in structures. </li></ul><ul><ul><li>The rays pass through the cracks and the cracks appear dark on film. </li></ul></ul>
  20. 20. GAMMA RAYS <ul><li>Shorter wavelength and higher frequency than X-rays </li></ul><ul><li>Carry the greatest amount of energy and penetrate the most. </li></ul><ul><li>Used in radiation treatment to kill cancer cells. </li></ul><ul><li>Can be very harmful if not used correctly. </li></ul>
  21. 21. <ul><li>SUMMARY </li></ul><ul><li>All electromagnetic waves travel at the same speed. (300,000,000 meters/second in a vacuum. </li></ul><ul><li>They all have different wavelength and different frequencies. </li></ul><ul><ul><li>Long wavelength-  lowest frequency </li></ul></ul><ul><ul><li>Short wavelength  highest frequency </li></ul></ul><ul><ul><li>The higher the frequency the higher the energy. </li></ul></ul>
  22. 22. Light as Particle <ul><li>Light also behaves like a particle </li></ul><ul><li>This particle is called a photon </li></ul><ul><li>The energy of a photon is dependent on its frequency </li></ul><ul><li>A photon is like a little packet (quantum) of electromagnetic energy. </li></ul>
  23. 23. Where do photons come from? <ul><li>Photons come from atoms </li></ul><ul><li>Atoms absorb and emit photons at certain specific frequencies. </li></ul><ul><li>This is because the electrons can only be in certain orbitals. </li></ul>
  24. 24. Atomic Emission e -
  25. 25. This means… <ul><li>Atoms of an specific element absorb or emit only specific frequencies of electromagnetic energy. </li></ul><ul><li>This is called the absorption or emission spectrum. </li></ul>
  26. 26. Using this in astronomy <ul><li>Astronomers can use these spectra to determine the composition of stars and planets and other stellar objects. </li></ul>
  27. 27. The Sun’s Emission Spectrum
  28. 28. Wave particle duality
  29. 29. <ul><li>SUMMARY </li></ul><ul><li>Light can also behave light particles called photons. </li></ul><ul><li>These photons come from the electrons in atoms. </li></ul><ul><li>Because electrons can only be in specific orbitals, only specific frequencies are emitted or absorbed. </li></ul><ul><li>These specific frequencies (spectrum) can be used to determine what elements are present. </li></ul>
  30. 30. Spectroscopy <ul><li>Using wavelength/frequency to determine composition </li></ul><ul><li>Can use light emitted </li></ul><ul><ul><li>emission </li></ul></ul><ul><li>Or light absorbed </li></ul><ul><ul><li>absorption </li></ul></ul>
  31. 31. Light and temperature <ul><li>Electromagnetic spectrum also tells temperature </li></ul><ul><li>More heat = more energy </li></ul><ul><li>More energy = higher frequency </li></ul><ul><li>Higher frequency = More heat </li></ul>
  32. 32. Thermal radiation <ul><li>electromagnetic radiation emitted an object because of the object's temperature </li></ul>
  33. 33. Temperature of Stars <ul><li>Gamma and x-ray emitters are hottest </li></ul><ul><li>Blue stars are hotter </li></ul><ul><li>Red stars are colder </li></ul><ul><li>Radio emitters are coldest </li></ul>
  34. 34. Kelvin <ul><li>Kelvin is the astronomer’s temperature scale </li></ul><ul><li>Abbreviation : K </li></ul><ul><li>K= ºC + 273 </li></ul><ul><li>So… 0K = -273ºC </li></ul>
  35. 35. What’s colder than cold? <ul><li>Absolute zero! </li></ul><ul><li>0K </li></ul><ul><li>Absolutely NO atomic motion </li></ul><ul><ul><li>None </li></ul></ul><ul><ul><li>Nada </li></ul></ul><ul><ul><li>Zip </li></ul></ul><ul><ul><li>Zilch </li></ul></ul><ul><ul><li>No not even a little. </li></ul></ul><ul><li>Deep space is just a few degrees above absolute zero </li></ul>
  36. 36. Summary <ul><li>Spectroscopy is using electromagnetic radiation to determine composition </li></ul><ul><li>Thermal radiation is electromagnetic radiation emitted due to temperature </li></ul><ul><li>This can be used to determine the temperature and composition of stellar objects </li></ul><ul><li>Absolute zero (0K) is no atomic motion </li></ul>
  37. 37. Manipulating Light <ul><li>Manipulating, or working with, light is what astronomers do </li></ul><ul><li>We have two main ways to manipulate light: </li></ul><ul><ul><li>Refraction </li></ul></ul><ul><ul><li>Reflection </li></ul></ul>
  38. 38. Refraction <ul><li>Changing the direction of light as it passes through some medium </li></ul><ul><li>For example: </li></ul><ul><ul><li>Straw in drink </li></ul></ul><ul><ul><li>lenses </li></ul></ul>
  39. 39. Refraction
  40. 40. Refracting Telescope <ul><li>Focus light through a series of lenses </li></ul><ul><li>Like what Galileo used </li></ul>
  41. 41. Reflection <ul><li>Redirection of electromagnetic radiation </li></ul><ul><li>Can be done with more than just visible light! </li></ul>
  42. 42. Reflecting Telescopes <ul><li>Focus light through a series of mirrors </li></ul><ul><li>Invented by Isaac Newton </li></ul>
  43. 43. Reflecting Telescopes <ul><li>Allow for larger telescopes </li></ul>English astronomer William Herschel built this huge reflecting telescope in the late 1700s.
  44. 44. Radio Telescopes <ul><li>Work like visible light reflector scopes </li></ul><ul><li>Use the radio frequencies </li></ul>
  45. 45. Radio Telescopes
  46. 46. Radio Astronomy <ul><li>Cassiopeia in visible light </li></ul><ul><li>Cassiopeia A in radio </li></ul>
  47. 47. Photoelectric Effect <ul><li>Light hitting an object causes electrons to be released </li></ul><ul><li>Must be correct wavelength/frequency </li></ul><ul><ul><li>(amplitude not important) </li></ul></ul>
  48. 48. Photoelectric effect in astronomy <ul><li>Solar panels for spacecraft </li></ul><ul><li>Digital photography </li></ul>
  49. 49. Photography in Astronomy <ul><li>As important a development as the telescope </li></ul><ul><li>Allows for sharing of information </li></ul><ul><li>Allows for precise measurements </li></ul>

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