slit diffraction in water??? Hello! I'm having trouble answer this hw problem: Suppose the entire apparatus (light of wavelength X nm from a distant source is incident on a slit Y mm wide, and the resulting diffraction pattern is observed on a screen Z m away) is immersed in water (n=1.33). Then what is the distance between the two dark fringes on either side of the central bright fringe? I know what I want to use the equation for Dark fringes in single-slit diffraction: sin(theta) = m*lamda/a in my case, m = 1 and a = y I'm not sure how to solve this problem now that the entire apparatus is immersed in water? I know water affects this, but how? Can you help me start this problem?