1. The problem statement, all variables and given/known data A double slit apparatus is held 1.2 m from a screen. (a) When red light (λ = 600 nm) is sent through the double slit, the interference pattern on the screen shows a distance of 12.5 cm between the first and tenth dark fringes. What is the separation of the slits? (b) What will be the difference in path length for the waves travelling from each slit to the tenth nodal line? 2. Relevant equations (a) xbright = λLm / d (b) path difference = (2m + 1)(λ / 2) 3. The attempt at a solution (a) xbright = λLm / d d = λLm / xbright d = (6.00 × 10-7 m)(1.2 m)(9) / 0.125 m d = 5.18 × 10-5 m d = 51.8 μm (b) path difference = (2m + 1)(λ / 2) path difference = [2(9) + 1][(6.00 × 10-7 m) / 2] path difference = 5.7 × 10-6 m path difference = 0.57 μm Hi! I'm little bit confused on this optics review question. I ended up using the bright fringe formula instead of the dark fringe formula for part (a) and I want to make sure I didn't do any colossal damage in the process. I also want to make sure I used the right formula for part (b). Thank you in advance!