Separation of two wavelengths in a diffraction grating.

[borvis]

Homework Statement

Light with two wavelengths (510.0 nm and 525.6 nm) is spread by a diffraction grating. On a screen 4 meters behind the grating we observe that the diffrence between the two second order maximum is 1 cm. What is the grating constant (d) ?

Homework Equations

I think i only need Snells Law for this problem, and some geometry.

The Attempt at a Solution

Im having som problem with the geometry of the solution. I need to find the distance to one of the maximums from the zero order maximum. I've found the relations:
sin(a)=(\lambda1/\lambda2)*sin(b)

 

[nickjer]

Snell's law? You might want to use the formula for maxima's of a diffraction grating:

d \sin \theta_m = m\lambda