In finding out refractive index of glass slab the following observations were made through travelling microscope 50 vernier scale division $=49 \mathrm{~MSD} ; 20$ divisions on main scale in each $\mathrm{cm}$ For mark on paper $\text { MSR }=8.45 \mathrm{~cm}, \mathrm{VC}=26$ For mark on paper seen through slab $\mathrm{MSR}=7.12 \mathrm{~cm}, \mathrm{VC}=41$ For powder particle on the top surface of the glass slab $\text { MSR }=4.05 \mathrm{~cm}, \mathrm{VC}=1$(MSR $=$ Main Scale Reading, VC = Vernier Coincidence) Refractive index of the glass slab is :