YDSE: Fringe Width & Fringe Positions question from JEE Main 2013

Answer: (d)

1. $S_1$ and $S_2$ lie on the line perpendicular to the screen, so the arrangement is symmetric about this axis.
2. Path difference at a point on the screen depends only on its distance from the foot of this axis: $\Delta x \approx d\cos\theta$.
3. Points with equal path difference lie on a circle centred on the axis, so each fringe is a circle.
4. So the answer is (d) concentric circles.