A small bulb is placed at the bottom of a tank containing water to a depth of 80 cm. What is the area of the surface of water through which light from the bulb can emerge out ? Refractive index of water is 1.33. (Consider the bulb to be a point source.)

Explanation

`r=0.8xxtani_(c) and sin i_(c)=1//1.33~=0.75`, where r is the radius (in m) of the largest circle from which light comes out and `i_(c)` is the critical angle for water-air interface, Area` = 2.6m^(2)`