Question

Find the apparent depth of the object, as seen by the observer.
[measured from the surface $\text{AB}$]

• A. $36\text{cm}$
• B. $18\text{cm}$
• C. $24\text{cm}$
• D. $16\text{cm}$

Answer 1

The correct option is A $36\text{cm}$


In this problem, observer is at $\text{AB}$.
Refracting index of observer's medium is ${\mu }_m=1.8$.

From formula of apparent depth,
$D_{\text{app}}=\sum \frac{d_i}{{\mu }_i/{\mu }_m}=\frac{20}{\left(\frac{2}{1.8}\right)}+\frac{15}{(\frac{1.5}{1.8})}$
$\Rightarrow D_{\text{app}}=18+18=36\text{cm}$

Hence, option $\left(a\right)$ is correct.