Question

In the set up shown in figure, the two slits `S_1` and `S_2` are not equidistant from the slit S. The central fringe at O is then

A. (a) Always bright
B. (b) Always dark
C. (c) Either dark or bright depending on the position of S
D. (d) Neither dark nor bright

Answer 1

Correct Answer - C
If path difference `Delta=(SS_1+S_1O)-(SS_2+S_2O)=nlambda`,
`n=0, 1, 2, 3, …` the central fringe at O is a bright fringe and if the path difference `Delta=(n-1/2)lambda`, `n=1, 2, 3, …` the central bright fringe will be a dark fringe.