Question

A fish looking up through the water sees the outside world contained in a circular horizon. If the refractive index of water is 4/3 and the fish is 12 cm below the surface of water, the radius of circle in centimetre is

• A. $36 \sqrt{5}$
• B. $4 \sqrt{5}$
• C. $36 \sqrt{7}$
• D. $\frac{36}{\sqrt{7}}$

Answer 1

Answer: (A)

$36 \sqrt{5}$

Answer 2

$\begin{array}{l} \sin i _{ c }=\frac{1}{ \mu }=\frac{ r }{\sqrt{ r ^{2}+ h ^{2}}} \\\ \text { Using } h =12 \,cm , \mu=4 / 3 \\\ \text { We get } r =\frac{36}{\sqrt{7}} cm \end{array}$