Four different experimental arrangements are listed below for attempting to observe an optical interference pattern on a distant screen.
(a) State whether a sustained interference pattern will be observed on the screen. Answer separately for A, B, C and D.
(b) For every arrangement in which interference is not observed, give one physical reason linked to the concepts of coherence or phase relationship.
(c) For every arrangement that does produce sustained fringes, identify the factor(s) that ensure a constant phase difference between the waves reaching corresponding points on the screen.