Monochromatic light of wavelength $500 \mathrm{nm}$ is used in a Young's apparatus. The separation between the two slits is $5\times {10}^{-4} \mathrm{m}$ and the screen is at a distance $1.0 \mathrm{m}$ from the slits. Now one of the slit is covered by a glass sheet of thickness $1.5\times {10}^{-6} \mathrm{m}$ and refractive index $1.5$. Find the lateral shift of the central maximum.