Light bends towards the normal when it travels from a less optically dense medium to a denser one.

Here's why:

* Optical Density: This refers to how much a medium slows down light. A denser medium (like glass) slows down light more than a less dense medium (like air).

* Normal: The normal is an imaginary line perpendicular to the surface between the two media at the point where the light ray hits.

* Bending: When light passes from one medium to another, its speed changes. This change in speed causes the light ray to bend, or refract.

Explanation:

When light enters a denser medium, it slows down. Since the light on one side of the ray is slowed down before the other side, this creates a difference in speed, causing the light ray to bend towards the normal.

Example:

Imagine a beam of light traveling from air (less dense) into water (denser). The light ray will bend towards the normal as it enters the water.