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Doppler Effect and Reflection

  1. Jan 9, 2008 #1
    I am having a friendly argument with a friend.
    If a light source was moving towards a colored object at high speeds in a completely dark area, would the color shift due to the Doppler effect be doubled?

    Possible theories are no (which we agree is wrong)
    Yes (which may be right)
    Or simply that the Doppler equation is applied twice, the second time on the result of the first equation. (Most probbable).

  2. jcsd
  3. Jan 9, 2008 #2


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    ... that's one hellava argument against democracy if I ever heard one.

  4. Jan 9, 2008 #3
    Sorry, I misworded the question, The point of observation is supposed to be from the light source. (such as a car with headlights).
  5. Jan 9, 2008 #4


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    If you shine white headbeam light at a red object, the returning light contains mostly red wavelengths, because those are the wavelengths reflected. The Doppler shift in the incident light will still leave about as much intensity in the red. Thus the light reflected back toward you will be the same as if you had been at rest. The only Doppler you will observe will be the relativistic Doppler shift for your movement toward the red object.
    The Doppler shift for police radar is different, because they use a relatively pure frequency, so you can't use this in court.
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