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Geometrical optics is the science that deals with the behavior of lenses on the basis of the geometrical relations between the entering and emerging ray paths. It takes no account whatever of the fact that a beam of light is really a train of waves having the power to interfere with the waves in other light beams and the ability to be âpolarized.â These aspects of light are generally grouped under the heading of physical optics, and will be discussed in the next chapter.
For the present, then, we shall regard a ray of light as nothing more than a path or track along which the light energy flows. When a ray strikes the surface of separation between two transparent media, such as air and glass, it is abruptly bent and sets off in the second medium in a new direction. This property is known as refraction, the amount of the bending being given by the well-known Snell's law.
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