Distance between m=1 bright fringes for red and green laser on diffraction grating

[Barry Melby]

Homework Statement

You shine a red (λ = 650 nm) laser beam and a green (λ = 532 nm) laser beam at a diffraction grating that has 400 slits/mm to create an interference pattern on a wall 2.30 m from the grating. If the two lasers are directly on top of each other, how far apart are the two m = 1 bright fringes from each other?

Homework Equations

The Attempt at a Solution

(650*10^-9)(2.30) / (1/400)(.001) - (532*10^-9)(2.30) / (1/400)(.001) = 0.10856 m

This is incorrect, however. What did I miss?

 

[TSny]

You calculation appears to assume a "small angle approximation". Check to see if the angles of diffraction for the two wavelengths are "small".