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# Redshift changing wavelength watch

1. 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
2. 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
3. Red shift (z) is a dimensionless number. You should know of an equation that would work here...
4. There aren't any units for the redshift
5. (Original post by Geek1337)
There aren't any units for the redshift
That's right, yes.

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?)
65.63 + 656.3 = 721.93 (answer A)

I'm just really unsure if I'm using the right equation
7. 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
http://hyperphysics.phy-astr.gsu.edu...v/reldop2.html
9. I honestly haven't seen any of those equations before...
10. (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.
11. I don't know how to use

either
12. Work out the change in wavelength - then add it to the original wavelength to get the new wavelength.
13. (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?)
65.63 + 656.3 = 721.93 (answer A)
14. yup
15. Cool, problem solved.
Thanks for all your help everyone
16. Hello.

Edited because I posted in the wrong thread lol.

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