- #1

leroyjenkens

- 590

- 48

## Homework Statement

What's the doppler shift (Δf) of the object moving away from us if we measure a wavelength of light λ=1.55μm emitted from it and it's at a distance of 10 megaparsecs? And is the object red or blue shifted?

Added information to the problem is for each megaparsec the object is away from us, it's moving 74 km/s faster.

## Homework Equations

[tex]f=\frac{c}{λ}[/tex]

[tex]f=\frac{\sqrt{1-β}}{\sqrt{1+β}}f_0[/tex]

For source and receiver receding from each other.

[tex]f=\frac{\sqrt{1+β}}{\sqrt{1-β}}f_0[/tex]

For source and receiver approaching each other. (shouldn't need this one)

β = [itex]\frac{v}{c}[/itex]

## The Attempt at a Solution

I find frequency first, by using equation #1, and converting the micrometers of the wavelength to meters. I find it to be 5.1666667x10

^{-15}.

Then I plug that into the second equation to find f

_{0}, which is 5.1794269x10

^{-15}

f

_{0}is larger than f. Does f

_{0}stand for initial frequency? Well, the difference in frequencies is f

_{0}-f, which is 1.276x10

^{-17}

So I assume that means the frequency was stretched? Which means it was redshifted?

I guess if it was compressed, I would have received a negative number, and that would have meant it was blueshifted?

Thanks.