chapter_22 - Light is bent(refracted as it passes through...

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726 22 CHAPTER Reflection and Refraction of Light O U T L I N E 22.1 The Nature of Light 22.2 Reflection and Refraction 22.3 The Law of Refraction 22.4 Dispersion and Prisms 22.5 The Rainbow 22.6 Huygens’ Principle 22.7 Total Internal Reflection Peter Bowater/Photo Researchers, Inc. Light has a dual nature. In some experiments it acts like a particle, while in others it acts like a wave. In this part of the book, we concentrate on the aspects of light that are best under- stood through the wave model. First we discuss the reflection of light at the boundary between two media and the refraction (bending) of light as it travels from one medium into another. We use these ideas to study the refraction of light as it passes through lenses and the reflection of light from mirrored surfaces. Finally, we describe how lenses and mirrors can be used to view objects with telescopes and microscopes and how lenses are used in photog- raphy. The ability to manipulate light has greatly enhanced our capacity to investigate and understand the nature of the universe. 22.1 THE NATURE OF LIGHT Until the beginning of the 19th century, light was modeled as a stream of particles emitted by a source that stimulated the sense of sight on entering the eye. The chief architect of the particle theory of light was Newton. With this theory, he pro- vided simple explanations of some known experimental facts concerning the nature of light—namely, the laws of reflection and refraction. Most scientists accepted Newton’s particle theory of light. During Newton’s lifetime, however, another theory was proposed. In 1678, the Dutch physicist and astronomer Christian Huygens (1629–1695) showed that a wave theory of light could also explain the laws of reflection and refraction. The wave theory didn’t receive immediate acceptance, for several reasons. First, all the waves known at the time (sound, water, and so on) traveled through some sort of medium, but light from the Sun could travel to Earth through empty space. Light is bent (refracted) as it passes through water, with different wavelengths bending by different amounts (which is called dispersion). Together with reflection, these physical phenomena lead to the creation of a rainbow when light passes through small, suspended droplets of water.
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22.2 Reflection and Refraction 727 Further, it was argued that if light were some form of wave, it would bend around obstacles; hence, we should be able to see around corners. It is now known that light does indeed bend around the edges of objects. This phenomenon, known as diffraction , is difficult to observe because light waves have such short wavelengths. Even though experimental evidence for the diffraction of light was discovered by Francesco Grimaldi (1618–1663) around 1660, for more than a century most scientists rejected the wave theory and adhered to Newton’s particle theory, proba- bly due to Newton’s great reputation as a scientist.
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