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Doppler Frequency Equation Question

  1. Apr 2, 2012 #1
    In my physics books it gives an equation of frequency for a moving observer as

    f'= v'/λ =v+u/λ. Since λ=v/f it was converted to f'=v+u/(v/f) = (v+u/v)f

    I understand this much of the equation, but the final Algebraic factoring that I don't get is they said this equation is f'= (1+u/v)f

    I just don't get how v+u/v was changed to 1+u/v.

    Any explanation here would be helpful.

  2. jcsd
  3. Apr 2, 2012 #2


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    Hi Nathan777! :smile:

    You've left out the brackets! :rolleyes:

    (Also, your dimensions obviously don't match: you can't add things of different dimensions, ie different units, eg you can't add a v to a u/λ. :wink:)

    It should be written …

    f'= v'/λ =(v+u)/λ. Since λ=v/f it was converted to f'=(v+u)/(v/f) = ((v+u)/v)f = (1 + u/v)f​
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