Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Doppler effect and Speed of light

  1. Nov 27, 2013 #1
    If light from a moving away object, such as a star, would appear red-shifted (and blue in case of approaching object), why don't we conclude that the speed of light is affected from that. Doesn't it mean that since light from a moving away object appear red, then the speed of light with respect to us has reduced (C-V) ?
     
  2. jcsd
  3. Nov 27, 2013 #2

    phinds

    User Avatar
    Insights Author
    Gold Member

    No, the FREQUENCY is affected. That's what red/blue shifted means. The speed is unchanged.
     
  4. Nov 27, 2013 #3

    Dale

    User Avatar
    Insights Author

    Staff: Mentor

    The frequency and the speed are related by ##v=f\lambda## where ##\lambda## is the wavelength. With light ##\lambda## changes as the reciprocal of ##f##, so ##v## remains constant.
     
  5. Nov 27, 2013 #4
    So, this must be true even in case of sound. So, does the speed of sound also remain constant in such case?
     
  6. Nov 27, 2013 #5

    Bandersnatch

    User Avatar
    Science Advisor
    Gold Member

    When a car passes you by, and you hear the pitch of its engine's sound change, do you conclude the speed of sound in the air changed at that moment?
     
  7. Nov 27, 2013 #6

    Dale

    User Avatar
    Insights Author

    Staff: Mentor

    Yes, the speed of sound depends on the properties of the air (temperature, density, velocity, etc.), not the speed of the emitter. Two different emitters, one stationary and one moving but otherwise identical, will produce sound waves at different frequencies and wavelengths, but the same speed.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Doppler effect and Speed of light
Loading...