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Geometrical Optics

critical angle, light rays, plastic tube, medical examination, deviation

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Given that a ray is bent away from the normal when it enters a less dense medium and that the deviation from the normal increases as the angle of incidence increases, an angle of incidence exists, known as the critical angle, such that the refracted ray makes an angle of 90 with the normal to the surface and travels along the boundary between the two media. If the angle of incidence is increased beyond the critical angle, the light rays will be totally reflected back into the incident medium. Total reflection cannot occur if light is traveling from a less dense medium to a denser one. The three drawings in Fig. 6 show ordinary refraction, refraction at the critical angle, and total reflection. In the late 20th century, a new, practical application of total reflection was found in the use of fiber optics. If light enters a solid glass or plastic tube obliquely, the light can be totally reflected at the boundary of the tube and, after a number of successive total reflections, emerge from the other end. Glass fibers can be drawn to a very small diameter, coated with a material of lower refractive index, and then assembled into flexible bundles or fused into plates of fibers used to transmit images. The flexible bundles, which can be used to provide illumination as well as to transmit images, are valuable in medical examination, as they can be inserted into various openings.

Article key phrases:

critical angle, light rays, plastic tube, medical examination, deviation, illumination, boundary, drawings, century, surface, images, Given, end, media

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