The Law of Refraction, also known as Snell's Law, describes how light changes direction when it passes from one medium to another, such as from air to water. This bending occurs because light travels at different speeds in different materials. The law can be mathematically expressed as the ratio of the sine of the angle of incidence to the sine of the angle of refraction being constant for any two media. When light enters a denser medium, like water, it slows down and bends towards the normal line, which is an imaginary line perpendicular to the surface. Conversely, when light exits a denser medium into a less dense one, it speeds up and bends away from the normal. This principle is essential in understanding how lenses, such as those in glasses or cameras, focus light.