A small object is placed at the centre of the bottom of a cylindrical vessel of radius 3cm and height 4cm filled completely with water. Consider the ray leaving the vessel through a corner. Suppose this ray and the ray along the axis of the vessel are used to trace the image. Find the apparent depth of the image and the ratio of real depth to the apparent depth under the assumptions taken. Refractive index of water = 1.33
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According to the figure, $\frac{\text{x}}{3}=\cot\text{r} \ ...(1)$
Again, $\frac{\sin\text{i}}{\sin\text{r}}=\frac{1}{1.33}=\frac{3}{4}$
$\Rightarrow\sin\text{r}=\frac{4}{3}\sin\text{i}=\frac{4}{3}\times\frac{3}{5}=\frac{4}{5} \ \Big(\text{because}\sin\text{i}=\frac{\text{BC}}{\text{AC}}=\frac{3}{5}\Big)$
$\Rightarrow\cot\text{r}=\frac{3}{4} \ ...(2)$
From (1) and (2)
$\Rightarrow\frac{\text{x}}{3}=\frac{3}{4}$
$\Rightarrow\text{x}=\frac{9}{4}=2.25\text{cm}.$
$\therefore \ $ Ratio of real and apparent depth = 4 : (2.25) = 1.78
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