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Gre Problem # 60

  1. Aug 31, 2004 #1
    Hello brainy people,
    I did solve this problem, but my answer is double the correct one, I wonder what went wrong.
    here it is:
    The Lyman alpha spectral line of hydrogen (lambda = 122 nm) differs by 1.8*10^-12 m in spectra taken at opposite ends of the sun's equator. What is the speed of a particle on the equator due to the Sun's rotation, in kilometers per second?

    I used the doppler formula, delta lambda/lambda = v/c
    so I got c = 4.4 Km/s, but the correct answer is 2.2 km/s

    thanks for your effort
  2. jcsd
  3. Aug 31, 2004 #2


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    Staff Emeritus
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    Gold Member

    One one limb of the Sun, the particles are approaching you. On the other, they are receding from you. The difference from one side to the other is 4.4 km/s, but the particles are only moving 2.2 km/s; they're just moving in opposite directions on opposite limbs of the Sun.

    - Warren
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