Explain with the help of a labeled 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.

The pencil appears bent at the water surface because the light refracts at the air water interface and bends away from the normal. The makes the observer in air feel that the pencil is bent inside water as shown in the figure.

if water is replaced with an optically denser medium the bending will increase , using Snell's law:

${\mu }_1\sin i={\mu }_2\sin r$, More ${\mu }_1$ more will be angle of refraction i.e.$\sin r$.

μ1sini=μ2sinr