Translations of Encyclopedia about Physics

Light Refraction

By refraction we understand the change in the direction and speed of light waves which occurs when the waves move from one environment into another or when they hit their surface boundary. For example, when light rays fall on the surface boundary between air and water, a portion of the rays reflect where another portion continues on into the other environment, which is the water. But the direction of the light rays changes in this second environment, something referred to as light refraction. The normal (the perpendicular line at the point of impact of the light ray on the surface boundary) at the location of the light ray’s impact on the surface boundary is called the perpendicular or normal line of impact and the angle between the impacting ray and the normal is called the angle of impact. The angle between the refracted ray and the normal line of impact is called the angle of refraction.

We can find such an example of refraction with more than just the surface boundary between air and water but generally any time light passes between such a surface boundary between two environments having different optical densities. Here, the change in the direction and speed of the light ray depends on the characteristics of the individual environments. If a light ray passes into a more dense environment, it slows down and becomes refracted. If the angle of impact is less than 45°, most of the ray is refracted and less is reflected. However, with angles larger than 45°, most of the light ray is reflected.

A special case occurs when the impacting light ray is at a 90° angle to the reflected light ray. In this case, the light ray does not penetrate the surface boundary into the second environment but rather travels along the surface boundary and only a small portion of it actually reflects. This phenomenon can be easily seen during the reflection of the water level.

Refraction of light also creates distant images, such as the reflection of air in the desert (fata morgana) or on the water’s surface (water level). A reflection of the air often occurs in very hot regions with a flat ground surface and occurs due to the existence of various atmospheric layers with different optical densities, which results in different degrees of refraction, eventually resulting in undisturbed refractions of light rays into several angles. This may make an object submerged in water appear to be closer than it actually is, an effect caused by the reflection off of air.

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