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Homework Help: Gravitational red shift question

  1. Aug 16, 2005 #1
    Why does the frequency of a photon emitted from the surface of a star decrease as it moves away from the star?
    if hf`=hf(1-GM/(R*c^2)
    then as the distance becomes larger, R becomes larger, so f`becomes smaller?
  2. jcsd
  3. Aug 16, 2005 #2


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    Homework Helper

    We use the fact that the total energy must remain constant.
    I'm not 100% sure, but I think t hat when leaving the star, the photon has to get out of the gravitation-field of the star, therefore its kinetic energy has to decrease since the potential energy is rising.
  4. Aug 17, 2005 #3
    hmm... that makes sense, but the mathematical equation looks weird...
    it seems to say otherwise~
  5. Aug 18, 2005 #4
    still a little weird~
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