- #1
Covenant32
- 15
- 0
Homework Statement
How fast would a star have to travel to make violet light (λ = 400 nm) appear to be blue (λ = 450 nm)? Assume the star is moving along the line that connects the star to the Earth.
Homework Equations
λr = λc / (c-Vr)
f= fo (c +- Vr / c +- Vs)
The Attempt at a Solution
Well, to be honest I am completely confused with this problem. It is the last problem in a homework set, so it is most likely the most difficult.
First attempt:
400-450 = -5e-8.
Now solve for v:
Δf = fs*((1+v)/c)
v = Δf*c/fs-1 = -5e-8*3e8/(4e-7) - 1 = -3.75E7 m/s, so the star would have to be moving away from you at 37,500,000 m/s.
Second attempt:
Vr = 450 * 3e8 / 400 * 3e8 = 1.125.
Neither are correct. Any assistance or guidance is truly appreciated. Thank you.