Refraction
Refraction is a fundamental concept in optics that describes the bending of light as it passes from one medium into another with a different optical density. When light travels through materials of varying density, such as air to water or glass, its speed changes, causing it to change direction. This phenomenon is responsible for various optical effects, including the way lenses in eyeglasses or contact lenses correct vision problems like nearsightedness or farsightedness. Refraction also explains why objects submerged in water appear distorted, as the light rays bend when transitioning between air and water, creating an apparent shift in position.