In Young's double slit experiment, two slits and are distance apart and the separation from slits to screen is (as shown in figure). Now if two transparent slabs of equal thickness 0.1 mm but refractive index 1.51 and 1.55 are introduced in the path of beam from and respectively. The central bright fringe spot will shift by _______ number of fringes. [2023]

(10)
