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Speed inorder to shift green light to blue light?

  1. Jul 31, 2010 #1
    Hypothetically if your in a jet or spaceship & are shining a green laser pen out the window how fast must you travel to cause the green light (570 nm) to change into low energy blue light (475 nm)
     
  2. jcsd
  3. Aug 1, 2010 #2

    Doc Al

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    Staff: Mentor

    Look up the Doppler effect.
     
  4. Aug 1, 2010 #3
    fo = fv/(v ± vs)? This isn't a hw problem & im not in a physics class, I was just curious
     
  5. Aug 1, 2010 #4

    Doc Al

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    Staff: Mentor

    You need to use the relativistic Doppler formula:

    [tex]f_o = f_s \sqrt{\frac{1 + \beta}{1 - \beta}}[/tex]

    where β = v/c

    Solve for β, then you'll have the speed. To convert wavelength to frequency, use c = fλ.

    This tells you the frequency shift seen by an observer when the light source moves toward him at speed v.
     
  6. Aug 1, 2010 #5
    Oh ok thanks I'll try it out
     
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