1. The problem statement, all variables and given/known data A Diffraction Barrier has 4200 openings per 1cm. A screen stands 2.00 m opposite of the Barrier. Say that for a certain class m, the maximums that correspond with two different wavelengths (589.00 nm & 589.6 nm) abstain from each other by 1.54 mm. What is the value of m? 2. Relevant equations tanθ = y/L sinθ = m*λ/d 3. The attempt at a solution Alright, we have: λ1 = 589.0 nm λ2 = 589.6 nm λ2 > λ1 => y2 > y1 => D = 1.54 mm = y2 - y1 tanθ ~ sinθ [θ is a small angle) Also, d = 1 cm/4200 = 2.38 * 10-4m So: D = L*m*(λ2 - λ1)/d <=> m = d*D/(λ2 - λ1)*L <=> ... <=> m = 3 My problem is that the naswer the book gives is m = 2. I run the numbers many times, and I always get 3. Am I doing something wrong? Is there a problem in the math or the logic? Any help is appreciated!