Question

A fish looks upward at an unobstructed overcast sky. What total angle does the sky appear to subtend? (Take refractive index of water as $\sqrt{2})$.

• A. ${180}^{\circ }$
• B. ${90}^{\circ }$
• C. ${75}^{\circ }$
• D. ${60}^{\circ }$

Answer 1

The correct option is B ${90}^{\circ }$

The fish can observe the sky only if refraction takes place.
If $TIR$ takes place, then image of sky cannot be observed.
i.e., $i<i_c$ and $i_c={45}^{\circ }$
So, angle subtended $=\frac{\pi }{2}$.