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Homework Help: Classical and Lorentzian transformation for doppler effect

  1. Dec 15, 2014 #1
    Hi everyone, I am having some problems understanding Bergmann's problems.

    Problem 3 from Chapter 4 from Intro to the Theory of Relativity by Bergmann

    1. Suppose that the frequency at a light ray is f with respect to a frame of reference S. Its frequency f′ in another frame of reference, S', depends on the angle α between the direction of the light ray and the direction of relative motion of S and S'. Derive both the classical and the relativistic equations stating how f' depends on f and the angle α. The light may be treated as a plane scalar wave moving with velocity c.

    Sol: classical ##f'= f(1-(v/c)cosα) ##
    relativistic ##f'= γ. (classical) ##(where γ is the Lorentz factor)

    What I did:

    ## x=ctCosα## , then ##x=fλtCosα##

    From Galilean transf. we have: ##x=x'-vt ,##

    then ##fλtCosα= f'λtCosα-vt , f = f' - \frac{v}{λCosα}, f = f' - (\frac{vf'}{cCosα})##

    What did I do wrong?
  2. jcsd
  3. Dec 20, 2014 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Dec 29, 2014 #3


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    I think maybe you swapped f and f'.
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