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Question
Explain with the help of a labelled ray diagram, why a pencil partly immersed in water appears to be bent at the water surface. State whether the bending of pencil will increase or decrease if water is replaced by another liquid which is optically more dense than water. Give reason for your answer.
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Solution
In the above figure, the portion BO of the pencil AO is immersed in water and it appears to be bent at point B. The light ray OC coming from the lower end O of the pencil passes from water to air and gets refracted away from the normal in the direction CX. Another ray OD is refracted in the direction DY. These two refracted rays, CX and DY, meet at point I, when they are produced backwards. Point I is nearer to the water surface than point O. Therefore, a virtual image of end O of the pencil is formed as point I.
So, human eye at position E sees the end O at point I; i.e., pencil appears to be bent.
If water is replaced by another liquid, which is optically denser than water, the bending of pencil will increase because an optically denser medium causes more refraction or more bending of light rays.
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