A monochromatic point source`(S_(1))` is at a distance d from a screen. Another identical source `(S_(2))` is at a large distance from the screen. The two sources are on a line which is perpendicular to the screen. Sources are coherent. What is the shape of interference fringes on the screen?
(b) Three identical coherent sources are placed on a straight line with two neighbouring ones separated by a distance `"d = 0.06 mm"`. The sources produce monochromatic light of wavelength `lambda" = 550.4 nm"`. A line AB is located at a distance D = 2.50 m from the sources and is perpendicular to line joining the three sources. Intensity of light at P with any one of the sources switched on is `I_(o)`. Find the intensity when all three sources are switched on. Distance of point P from O is` "y = 1.72 cm (see figure)"`