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Frequence of light of galaxy receding from earth

  1. Mar 10, 2010 #1
    1. The problem statement, all variables and given/known data

    Most of the galaxies in the universe are observed to be moving away from Earth. Suppose a particular galaxy emits orange light with a frequency of 5e14 Hz.

    1) If the galaxy is receding from Earth with a speed of 3325 km/s, what is the frequency of the light when it reaches Earth?

    2. Relevant equations

    f ' = f ( 1 - v/c)

    3. The attempt at a solution
    I did:

    f ' = 5e14 (1- 3.325e6/3e8) then converted Hz to fHz and got 4.9e29 but it was wrong.
  2. jcsd
  3. Mar 10, 2010 #2


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    Re: Frequency

    finger+calculator error

    You need to have an estimate of the answer to know if you hit the wrong buttons.
    3300km/s is tiny compared to light speed, so 1-v/c is going to be only slightly less than 1, so your answer is going to be slightly less than 5E14.

    "then converted Hz to fHz"
    what does this mean? whatever it means it was wrong
  4. Mar 10, 2010 #3
    Re: Frequency

    i reworked it and no clue what im doing wrong. and the answer says it's in fHz
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