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    The rest wavelength of a spectral line of hydrogen is observed from a galaxy at a wavelength of 656.3nm, if a galaxy has a redshift of 0.1, what wavelength will the hydrogen line appear when observed from the earth?

    I don't need the answer, I just want a bit of help about how I should go about working it out.

    Would I use:

    change in wavelength = redshift x original wavelength

    Or am I completely wrong?

    I'm not good at physics
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    Since the galaxy is moving away then I think you simply ADD the red shift. What are the units of the 0.1 ?

    Edit: Obviously, I was wrong. Sorry
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    Red shift (z) is a dimensionless number. You should know of an equation that would work here...
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    There aren't any units for the redshift
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    (Original post by Geek1337)
    There aren't any units for the redshift
    That's right, yes.
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    I have possible answers

    A 721.9 nm
    B 590.7 nm
    C 65.6 nm
    D 6563 nm
    E 694.3 nm

    I thought the way I was supposed to work it out is
    656.3 x 0.1 = 65.63 (which would be the change in wavelength?)
    Then add the change on
    65.63 + 656.3 = 721.93 (answer A)

    I'm just really unsure if I'm using the right equation
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    Well, without working it out, which of those answers would you expect to be correct? You can eliminate all by 2 without doing any calculation.

    The equation you want is z = \frac{\Delta \lambda}{\lambda}
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    This might be helpful.
    http://hyperphysics.phy-astr.gsu.edu...v/reldop2.html
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    I honestly haven't seen any of those equations before...
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    (Original post by Geek1337)
    I honestly haven't seen any of those equations before...
    The ones in that link are too complicated anyway. You don't need them.
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    I don't know how to use
    z = \frac{\Delta \lambda}{\lambda}
    either
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    Work out the change in wavelength - then add it to the original wavelength to get the new wavelength.
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    (Original post by teachercol)
    Work out the change in wavelength - then add it to the original wavelength to get the new wavelength.
    Like I said ages ago?

    656.3 x 0.1 = 65.63 (which would be the change in wavelength?)
    Then add the change on
    65.63 + 656.3 = 721.93 (answer A)
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    yup
    • Thread Starter
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    Cool, problem solved.
    Thanks for all your help everyone
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    Hello.

    Edited because I posted in the wrong thread lol.
 
 
 
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