91Ó°ÊÓ

For water$n=1.33$

For carbon tetrachloride $n=1.46$

Thickness of water layer$20.0mm$

Thickness of carbon tetrachloride layer$40.0mm$

We know that due to the change of medium of propagation of light, the speed of light will decrease resulting in the bending of rays. Observers in another medium will perceive the different depths of the object.

So, using the relative refractive index, we can calculate the apparent depth.

Formula:

Apparent depth

$d_a=d/n$

n is the relative refractive index of the medium in which the object is kept.

The relative refractive index of the carbon tetrachloride with respect to water is

$\begin{array}{c}n\text{'}=\frac{1.46}{1.33}\\ =1.1\end{array}$

So, the apparent depth of the coin from the bottom of the water layer is

$\begin{array}{c}{d}_a^{\text{'}}=\frac{40.0}{1.1}\\ =36.4mm\end{array}$

So, the distance of the coin perceived from the top of the water surface is

$\begin{array}{c}d\text{'}\text{'}=d\text{'}+\mathrm{thickness}\mathrm{of}\mathrm{water}\mathrm{layer}\\ =36.4+20\\ =56.4mm\end{array}$

Now, the apparent depth of the coin from the top of the water surface is

$\begin{array}{c}{d}_a=\frac{d\text{'}\text{'}}{1.33}\\ =\frac{56.4}{1.33}\\ =42.0mm\end{array}$

The apparent depth of the coin from the top of the water surface$d_a=42.0mm$

The above explanation can be illustrated using the following ray diagram.