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Many objects, such as people, clothing, leaves, and walls, have rough surfaces and can be seen from all sides. A mirror, on the other hand, has a smooth surface (compared with the wavelength of light) and reflects light at specific angles, as illustrated in Figure 25.7.
Figure I.11 shows an isosceles prism of angle \(\alpha\) and a ray of light passing through it. I have drawn just one ray of a single color. For white light, the colors will be dispersed , the violet light being deviated by the prism more than the red light.
The idea of geometrical optics is to understand the effects of refraction and reflection on beams of light, ignoring the effects of diffraction. This is really only Snell’s law and geometry. One application of these ideas will be in the discussion of the rainbow in the next section.
The ray nature of light is used to explain how light refracts at planar and curved surfaces; Snell's law and refraction principles are used to explain a variety of real-world phenomena; refraction principles are combined with ray diagrams to explain why lenses produce images of objects.
Explore bending of light between two media with different indices of refraction. See how changing from air to water to glass changes the bending angle. Play with prisms of different shapes and make rainbows.
When a ray of light encounters an interface between two transparent media, a portion of it is reflected and a portion is refracted, and it is natural to ask, even during an early introduction to the subject, just what fraction is reflected and what fraction is refracted.
The principles of geometric optics describe the interactions of light on a macroscopic scale. Geometric optics is mainly used to determine how light will change direction and form images through reflection or refraction. The path of light is approximated by rays that travel in straight lines.
