Question

A fish looking up through water sees the outside world contained in a circular horizon. If the refractive index of water is $\frac{4}{3}$ and the fish is 12 cm below the surface, the radius of this circle (in cm) is

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

Answer 1

The correct option is D $\frac{36}{\sqrt{7}}$

if the fish sees the world in a circular horizon, then the ray going out of the water is making a critical angle. Find the angle and compute the radius of the circle.