(a) Explain why, a stick half immersed in water appears to be bent at the surface. Draw a labelled diagram to illustrate your answer.(b) A coin in a glass tumbler appears to rise as the glass tumbler is slowly filled with water. Name the phenomenon responsible for this effect.
(a) A stick half immersed in water appears to be bent at the surface due to the refraction of light when it passes from water into the air.
In the figure given below, the half portion $BO$ of stick $AO$ is immersed in water and it appears to be bent at point $B$. A ray of light $OC$ coming from the lower end $O$ of the stick passes from water to air and gets refracted away from the normal in the direction $CX$. Another ray $OD$ gets refracted along with in the direction $DY$. The two refracted rays, $CX$ and $DY$ when produced backwards, appear to meet at a point $I$. And, point $I$ is nearer to the water surface than point $O$. Thus, a virtual image of the end $O$ of the stick is formed as $I$. Hence, the human eye at position $E$ sees the end $O$ of the stick at $I$, so the stick appears to be bent.
(b) A coin in a glass tumbler appears to rise as the glass tumbler is slowly filled with water. The phenomenon responsible for this effect is refraction.
Explanation
On adding water to the glass tumbler the coin appears to rise due to the refraction of light which takes place when it goes from water into air. Thus, a virtual image of the coin is formed nearer to the water surface.
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