GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY
Light refraction at the critical angle When light is incident from a more optically dense medium onto a less optically dense medium (for example, from glass onto air) it refracts (bends) away from the normal to the surface between the media. The angles of incidence and refraction are related through the Snell's law. When the incidence angle is equal to critical angle refracted beam travels right along the surface, as demonstrated in this photograph using a Helium-Neon laser beam (633 nm). Characteristic laser speckle pattern is apparent.
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