1. The problem statement, all variables and given/known data Parallel rays of light pass of wavelength 540nm throught a 0.4mm slit. The intensity of the central maximum on a diffraction pattern 1.5m away is Io. At what distance from the central maximum does the intensity fall to Io/2? 2. Relevant equations I = Io sin^2 (pi a y / lambda d) / (pi a y / lambda d)^2 (????) 3. The attempt at a solution Okay, I worked out the distance from the central maximum to the first minimum to be 2.03mm, so it's obviously less than that... beyond that, I'm stuck. Any ideas?