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Total internal reflection

Figure 1: Light reflection and refraction at a glass-air boundary.

Figure 1: Light reflection and refraction at a glass-air boundary.

A light ray is reflected and refracted when it encounters the boundary between two different transparent mediums. At any angle of incidence greater than the critical angle αlim, light is totally reflected back into the glass medium.

For example, the figure shows what happens to the light ray when it encounters the interface between glass (more dense medium) and air (less dense medium). The critical angle is the angle of incidence above which total internal reflection occurs.