Speed inorder to shift green light to blue light?

1. Jul 31, 2010

Moviemann345

Hypothetically if your in a jet or spaceship & are shining a green laser pen out the window how fast must you travel to cause the green light (570 nm) to change into low energy blue light (475 nm)

2. Aug 1, 2010

Staff: Mentor

Look up the Doppler effect.

3. Aug 1, 2010

Moviemann345

fo = fv/(v ± vs)? This isn't a hw problem & im not in a physics class, I was just curious

4. Aug 1, 2010

Staff: Mentor

You need to use the relativistic Doppler formula:

$$f_o = f_s \sqrt{\frac{1 + \beta}{1 - \beta}}$$

where β = v/c

Solve for β, then you'll have the speed. To convert wavelength to frequency, use c = fλ.

This tells you the frequency shift seen by an observer when the light source moves toward him at speed v.

5. Aug 1, 2010

Moviemann345

Oh ok thanks I'll try it out