Two coherent sources S1, and S2, are situated on the X-axis. The screen is in Y-Z plane as shown in fig. (2). The shape of the fringe on screen is

When screen is perpendicular to the line joining the sources S1 and S2, then the shape of fringe is circular. It should be remembered that when the screen is parallel to the line joining coherent sources S1, and S2, then the shape of fringe is hyerbolic, of course, the central bright fringe is straight line.