1. The problem statement, all variables and given/known data Show that the seperation of the two coherent sources is given by d=2aA(n-1) where n is the refactive index of prism. 2. Relevant equations from youngs double slit experiment y=Rm[itex]\lambda[/itex]/d 3. The attempt at a solution i have no idea how to derive this formula. ive seen it many times before but nowhere shows the derivation. i can see youngs experiment is similar, but fail to see a connection? help! there should be a picture attached to this post. hopefully!