Question

why the pencil is appear like bending when we insert it halfly filled water in a transparent glass

Answer 1

Due to the phenomenon of refraction.
"Refraction is the change in direction of wave propagation due to a change in its transmission medium"
hence we find the pencil appears to bend

Answer 2

This is a concept on refraction.

Refraction is the bending of light.

As light travels from one medium to another ,it is bent.

This happens since different mediums have different densities.

In our case as light travels from air to glass it is bent.

Again as it travels from glass to water it is bent.

This explains why the pencil appear bent.