Question

A mark is made on the bottom of a vessel and over this mark, a glass slab to thickness 3.5 cm and refractive index $\frac{7}{4}$ is placed. Now water (refractive index, $\frac{4}{3}$) is poured into the vessel so that the surface water is 8 cm above the upper surface of the slab. Looking down of normally through the water, the apparent depth of the mark below the surface of water will be :

• A. 6.33 cm
• B. 7.5 cm
• C. 8 cm
• D. 10 cm

Answer 1

Answer: (C)

8 cm

Refractive index = real depth / apparent depth.

$Apparentdepth=\frac{8}{\frac{4}{3}}+\frac{3.5}{\frac{7}{4}}=6+2=8cm$