Here's why:

* Density and Speed: Light travels slower in denser mediums. Think of it like trying to walk through a crowded room vs. an empty field.

* Angle of Incidence: The angle of incidence is the angle between the incoming light ray and the normal (a line perpendicular to the surface).

* Snell's Law: This law describes the relationship between the angles of incidence and refraction, and the indices of refraction of the two mediums. It essentially states that light bends more when it enters a denser medium.

Example:

* Light entering water from air: Air is less dense than water. The light ray will bend towards the normal as it enters the water.

Let me know if you'd like more examples!