# Speed inorder to shift green light to blue light?

by Moviemann345
Tags: blue shift, doppler effect, light, speed, wave
 P: 24 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)
 Mentor P: 41,475 Look up the Doppler effect.
 P: 24 fo = fv/(v ± vs)? This isn't a hw problem & im not in a physics class, I was just curious
Mentor
P: 41,475
Speed inorder to shift green light to blue light?

 Quote by Moviemann345 fo = fv/(v ± vs)? This isn't a hw problem & im not in a physics class, I was just curious
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.
 P: 24 Oh ok thanks I'll try it out

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