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 the circle in centimetre is

• A. $12\times 3\times \sqrt{5}$
• B. $\frac{12\times 3}{\sqrt{5}}$
• C. $12\times 3\times \sqrt{7}$
• D. $\frac{12\times 3}{\sqrt{7}}$

Answer 1

The correct option is D $\frac{12\times 3}{\sqrt{7}}$

sin $i_c=\frac{1}{\mu }=\frac{3}{4}$
tan $i_c=\frac{3}{\sqrt{7}}=\frac{R}{12}R=\frac{36}{\sqrt{7}}$