What happens to light when it enters a more dense medium?

When light enters a more dense medium, it slows down and bends toward the normal. This phenomenon is due to the change in the speed of light as it moves from one medium to another with different optical densities.

In a more dense medium, such as from air into water or glass, the speed of light decreases compared to its speed in air or vacuum. The bending of light toward the normal is explained by Snell's Law, which states that the angle of incidence is related to the angle of refraction when crossing the boundary between two media. Specifically, when light transitions into a denser medium, the incident light beam angles inward as it bends toward the normal—the hypothetical line that is perpendicular to the surface at the point of incidence.

This behavior is fundamental to understanding concepts in optics, such as the functioning of lenses and the principles of refraction. The bending effect is responsible for phenomena like the apparent bending of objects submerged in water and plays a crucial role in the design of optical instruments.