Q.
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) Always bright
B) Always dark
C) Either dark or bright depending on the position of S
D) Neither dark nor bright
Explanation
(c) Path difference, $x = \left( SS_{1} + S_{1}O \right) - \left( SS_{2} + S_{2}O \right)$
If$x = n\lambda$, the central fringe at O will be bright. If$x = (2n - 1)\lambda/2$, the central fringe at O will be dark.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.