Critical Angle

When light passes from one transparent medium to another, some of it is reflected, while the rest is transmitted through the material and is refracted or bent. At this exhibit, a plastic semi-circle which can be rotated lies in the path of a beam of light. As the semi-circle is turned, some of the light is bent in a new direction, while the remaining light is reflected. At the critical angle, all the light is internally reflected and the transmitted beam disappears.

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