Introduction To Basic Ray Optics

When an optical wave travels between mediums, its velocity changes and it is deflected through a phenomenon known as refraction. The magnitude of these changes (relative to the speed of light in a vacuum) depends on a characteristic value for each material called the index of refraction, typically denoted by the letter n. Air has an index of refraction very close to 1.0, while glass typically has an index of refraction near 1.5.

Prisms, lenses, and our own eyes use this refraction to their advantage. By controlling the material (and thus the index of refraction) and the shape of the surface, one can manipulate the direction of light. Prisms can be used to bend a beam of light, and the angle of their surfaces controls the magnitude of these bends. Since prisms are created using flat surfaces, they are only capable of applying a fixed refraction angle on light, regardless of where the light is incident on its surface. A lens, on the other hand, has a curved surface that enables it to focus or diverge collimated light.