Why does the pencil appear like bending when we insert it halfly filled with water in a transparent glass?

Hint:To answer this question, we first need to understand how we are able to see an object. To see an object, we primarily rely on two factors: eyes and light. When a ray of light from a source of light (usually the sun) strikes an object, it is mirrored in all directions. Our eyes then receive the reflected light, which our brain interprets as an entity.

Complete answer:
Refraction of light:The bending of light (as well as sound, water, and other waves) as it moves through one transparent material into another is known as refraction. Lenses, magnifying glasses, prisms, and rainbows are all possible because of this bending by refraction. Even our eyes are reliant on light bending.

Optical density: A measurement of an optical medium's transmittance. Optical density is the ratio of the intensity of light falling on a material to the intensity transmitted in spectroscopy, and it is defined as the ratio of the intensity of light falling on a material to the intensity transmitted.

Because of refraction of light, a pencil submerged in water looks bent. The refraction causes the location of the pencil component inside the water to appear to change. As water is replaced with another liquid that has a higher optical density than water, the pencil bends further.

Note: The frequency of light does not change when it passes from one medium to another. The velocity and wavelength, on the other hand, change. A ray of light bends as it travels from one optical medium to another with different refractive indices.