If a light ray passes from one medium into another medium, it changes its direction, or its path is “bent”. However, if the angle of the light ray is very flat, it cannot penetrate the second medium and will be completely reflected at the boundary.

This phenomenon is called total reflection. We are familiar with total reflection, for example, in deep sea diving. Divers underwater can only see a fraction of what is going on above water, as light bounces off the surface of the water. Total reflection also has significant technological applications. For example, when light is guided along a glass fibre – the fundament of modern telecommunication and data transmission.

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