JEE Main 2023 — Wave Optics Question with Solution

In Young's double slit experiment, two slits $$S_1$$ and $$S_2$$ are '$$d$$' distance apart and the separation from slits to screen is $$\mathrm{D}$$ (as shown in figure). Now if two transparent slabs of equal thickness $$0.1\mathrm{mm}$$ but refractive index $$1.51$$ and $$1.55$$ are introduced in the path of beam $$(\lambda =4000$$ $$\stackrel{o}{A}$$) from $${\mathrm{S}}_1$$ and $${\mathrm{S}}_2$$ respectively. The central bright fringe spot will shift by ___________ number of fringes.