Critical Angle indicates the point at which reflected and refracted light come together. When light passes through any material, 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 that 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 refracted light is internally reflected and the transmitted beam disappears.