What occurs when light moves from a slower medium to a faster medium?

When light moves from a slower medium to a faster medium, it bends away from the normal. This behavior is rooted in the principles of refraction, which describe how light changes direction when it passes between materials with different densities or propagation speeds.

In a slower medium, such as water or glass, light travels more slowly than it does in a faster medium like air or vacuum. As light transitions to the faster medium, its speed increases, and this change in speed causes the light wave to change direction. The transition angle is such that the light ray refracts away from the normal line (an imaginary line that is perpendicular to the boundary surface).

To visualize this, think of a car transitioning from a rough road (slower medium) to a smooth highway (faster medium). As the car accelerates, it veers off to the side, not toward the center of the road (the normal), but towards a wider path. Similarly, light moving from a denser medium to a less dense medium bends outward, moving away from the normal.