Snell’s Law explains how light changes direction, or bends, when it travels from one medium to another—such as from air into water or from glass into air. This bending occurs because light moves at different speeds in different materials. The extent of bending depends on the refractive index of each medium, which is a measure of how much the medium slows down light.
When light enters a denser medium (with a higher refractive index), it slows down and bends toward the normal—an imaginary line perpendicular to the surface at the point of contact. Conversely, when light enters a less dense medium, it speeds up and bends away from the normal.
Snell’s Law quantitatively relates the angle of incidence (incoming angle) to the angle of refraction (bending angle) and is fundamental in optics. It explains how lenses work, why pools appear shallower than they are, and how rainbows form.