In a double-slit experiment with blue light of 645 nm, the distance between the slits was calculated using the formula d = (Lmλ)/X, yielding a result of 2.68 mm. A follow-up question involved determining the separation between the central bright fringe and the third dark fringe, which requires using the dark fringe formula X/L = (2m + 1)λ/2d. The discussion also covered single-slit diffraction, with the formula y = (mλD)/w used to find the distance to dark fringes, emphasizing the importance of distinguishing between equations for single and double slits. Participants clarified methods for calculating distances and confirmed the correctness of their approaches. Overall, the thread provided detailed insights into applying the double-slit and single-slit equations in various experimental scenarios.