Question

A fish is swimming in a river at a depth of 20 cm from the surface of the water. Refractive Index of water is $\frac{4}{3}$. At what depth will an eagle flying above the water and exactly above the fish will see the fish?

• A. 10 cm
• B. 20 cm
• C. 26.66 cm
• D. 15 cm

Answer 1

The correct option is D

15 cm

Given:
Refractive index of water, ${\mu }_{water}$ ​ = $\frac{4}{3}$
Real depth of fish from surface of water $=20cm$
In the given situation,
Refractive Index of water $={\mu }_{water}=\frac{Realdepth}{Apparentdepth}$
$\Rightarrow Apparentdepth=\frac{Realdepth}{{\mu }_{water}}$
$\Rightarrow Apparentdepth=\frac{20}{\frac{4}{3}}$
Therefore, $Apparentdepth=\frac{20\times 3}{4}$ = 15 cm. The eagle will perceive the fish to be at $15cm$ depth from the water surface.