In an interference arrangement similar to Young’s double slit experiment, but having four slits S₁, S₂, S₃ and S₄ are illuminated with coherent light wave of wavelength 400 nm. Sources are synchronized in way such that S₁, S₂ and S₄ have zero phase difference but S₃ is out of phase with others. In central wide part of screen intensity due to all individual slits is I₀. The consecutive slits are separated by a distance d = 1 mm. Distance between plane of slits and screen is D = 10 m

Point O is a point on screen lie on perpendicular bisector of S₁S₂. ‘P’ is the point on the screen closest to point ‘O’ having intensity 2I₀ when only S₁ and S₂ are illuminated. Now if all slits are illuminated, what will be new intensity at point ‘P’?