A diffraction grating has 1900 rulings/cm. On a screen 1.00 m from the grating, it is found that for a particular order m, the maxima corresponding to two closely spaced wavelengths of sodium (589.0 nm and 589.6 nm) are separated by 1.68 mm. Determine the value of m. Note: In this problem assume that the light is incident normally on the gratings.
m = ?