Four different experimental arrangements are listed below for attempting to observe an optical interference pattern on a distant screen.
A. Two parallel, independent sodium lamps illuminating their own slits.
B. A single, narrow sodium lamp illuminating two closely spaced slits cut in the same opaque screen.
C. Sunlight entering two slits of width 0.5mm after passing through a pinhole that is equidistant from the slits.
D. Two identical, phase-locked diode lasers illuminating two separate slits.
For each arrangement, answer the questions that follow.
a. (a) State whether a sustained interference pattern will be observed on the screen. Answer separately for A, B, C and D.
b. (b) For every arrangement in which interference is not observed, give one physical reason linked to the concepts of coherence or phase relationship.
c. (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.