Final answer:
When a wave passes from one material to another at an angle, the direction it travels changes in a process called refraction. This is described by Snell's Law and is due to the differing speeds of light in the respective media. The law of refraction can also be understood using Huygens's principle.
Step-by-step explanation:
When a wave, such as light, passes from one substance to another at an angle, it changes direction due to a phenomenon known as refraction. This occurs because the speed of light is different in the two media, leading to a change in the wave's speed and direction. The mathematical relationship that describes this behavior is known as Snell's Law, which is expressed as n1 sin θ1 = n2 sin θ2, where n1 and n2 are the refractive indices of the media and θ1 and θ2 are the angles of incidence and refraction, respectively.
Applying Huygens's principle to a wavefront illustrates how each point on the wavefront acts as a source of wavelets, which spread out and create a new wavefront. The wavelets in the second, slower medium do not travel as far, causing the wavefront to change direction toward the normal, or perpendicular, to the interface of the two media. This concept is fundamental to understanding how lenses and other optical devices manipulate light.
It is noteworthy that the law of refraction was discovered by the Arabian physicist Ibn Sahl in 984 and later by the Dutch mathematician Willebrord Snell.