Electromagnetic Spectrum 2

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Electromagnetic Spectrum 2

  1. 1. ELECTROMAGNETIC SPECTRUM<br />SPECTROSCOPY AND DOPPLER WAVE<br />
  2. 2. Other light characteristics<br />All radiant energy travels through the vacuum of space in a straight line at the rate of 300, 000 kilometers.<br />1 day = 26 billion kilometers. <br />
  3. 3. Other light characteristics<br />Photon<br />A quantum of visible light. (Quantum – smallest quantity of energy)<br />A photon has neither mass nor electrical charge.<br />A photon possesses energy and momentum.<br />A photon can exert pressure on matter. (Radiation pressure)<br />Responsible for “pushing” material away from a comet to produce its tail.<br />
  4. 4. Comet Hale-Bopp<br />
  5. 5. SPECTROSCOPY<br />Spectroscopy – study of the properties of light that depend on wavelength.<br />Newton’s study on prism initiated this study.<br />Also defined as the study of spectra, especially to determine the chemical composition of substances and the physical properties of molecules, ions and atoms.<br />
  6. 6. SPECTROSCOPY<br />Spectroscope<br />Instrument for studying spectra; an instrument for dispersing light usually light in the visible range, into a spectrum in order to measure it.<br />
  7. 7. SPECTROSCOPY<br />Three types of spectrum:<br />1. Continuous spectrum<br />2. Dark-line spectrum <br />(Absorption spectrum)<br />3. Bright-line spectrum<br />(Emission spectrum)<br />
  8. 8. SPECTROSCOPY<br />1. Continuous spectrum<br />Is produced by an incandescent solid, liquid or gas under high pressure.<br />Consists of an uninterrupted band of color.<br />E.g. Common light bulb<br />
  9. 9. Spectrum<br />
  10. 10. SPECTROSCOPY<br />2. Dark-line spectrum (Absorption spectrum)<br />Is produced when “white” light is passed through a comparatively cool gas under low pressure.<br />Gas absorbs selected wave length of light so the spectrum that is produced appears as a continuous spectrum, but with a series of dark lines. <br />
  11. 11. Spectrum<br />
  12. 12. SPECTROSCOPY<br />3. Bright-line spectrum (Emission spectrum) <br />It is a series of bright lines of particular wavelengths, depending on the gas that produces them.<br />These bright lines appear in the exact location as the dark lines that are produced by this gas in a dark-line spectrum (absorption).<br />
  13. 13. Spectrum<br />
  14. 14. SPECTROSCOPY<br />Most stars have dark line spectra.<br />Each element produces a unique set of spectral lines.<br />Each spectrum acts as a “finger print” of a star and is used to identify the element present.<br />
  15. 15. SPECTROSCOPY<br />Spectrum of a star (sun) explained in an overly simplified manner: <br />Central region – high pressure and high temperature – continuous spectrum.<br />Outer region – low pressure and low temperature – dark-line spectrum.<br />Dark lines in the spectrum are absorbed light. <br />
  16. 16. SPECTROSCOPY<br />The spectrum of the sun contains thousands of dark lines.<br />Over 60 elements have been identified by matching those lines with those of elements known on Earth.<br />
  17. 17. SPECTROSCOPY<br />TWO FACTORS CONCERNING A RADIATING BODY<br />1. If the temperature of a radiating surface is increased, the total amount of energy emitted is increased.<br />*Stefan Boltzman Law<br />The energy radiated by a body is directly proportional to the fourth power of its absolute temperature.<br />E.g. Star – Temperature doubled – energy emitted times 2 raise to 4 (16 times more energy.)<br />
  18. 18. SPECTROSCOPY<br />TWO FACTORS CONCERNING A RADIATING BODY<br />2. As the temperature of an object increases, a larger proportion of its energy is radiated at shorter wavelengths.<br />E.g. Heated Metal rod<br />Red – longer wavelength – hot<br />Blue – shorter wavelength – hotter<br />Red stars – hot<br />Blue stars - hotter<br />
  19. 19. DOPPLER EFFECT<br />Doppler effect<br />Explained by Christian Doppler in 1842.<br />change in frequency because of motion: a perceived change in the frequency of a wave as the distance between the source and the observer changes. <br />
  20. 20. DOPPLER EFFECT<br />When a light source is moving away, its light appears redder than it actually is.<br />The reason for it is that the wavelength is stretched.<br />Objects approaching have their wavelength waves shifted toward blue (shorter wavelength).<br />
  21. 21. Sodium lines<br />
  22. 22. DOPPLER EFFECT<br />Case analysis:<br />If a source of light is approached you at a very high speed (near the speed of light),<br />It would appear blue.<br />If you move with a speed of light the color of a stationary light source will appear blue. <br />
  23. 23. DOPPLER EFFECT<br />By using the Doppler effect<br />It reveals weather Earth is approaching or receding from a star or another celestial body.<br />The amount of shift allows to recalculate the rate at which the relative movement is occurring.<br />Larger Doppler shifts indicate higher velocities.<br />It is generally measured in from dark lines in the spectra of stars by comparing them with a standard spectrum produced in the laboratory. <br />
  24. 24. END OF PRESENTATION<br />

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