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Physics wave question

  1. May 29, 2009 #1
    1. The problem statement, all variables and given/known data

    a spectral line coming from a star in a binary system has a wavelength of 515.2 nm. in the lab the same spectral line would have a wavelength of 518.6 nm. what is the speed of the star in relation to earth?

    2. Relevant equations
    ??


    3. The attempt at a solution
    ??
     
  2. jcsd
  3. May 29, 2009 #2
    look up doppler effect, i'm not going to propose solution, because once you learn it for yourself -- I'm sure you'll figure it out in an instant (at least in a classical sense, not accounting the general relativity corrections -- there's not enough info in the problem to use that anyway).
     
  4. May 29, 2009 #3
    Or you could try relativistic doppler effect.
     
  5. May 30, 2009 #4
    Use the Dopple formula:

    f'=f.V/(V+Vs)

    V=c=3.10^8 m/s :speed of the radio wave.
    Vs: velocity of the star (source).

    U should find Vs, if it's positive then the star is moving away from the earth, otherwise it's moving closer.
     
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