Light and Optics
ight is basic to almost all life on the Earth. Plants convert the energy trans-
ferred by sunlight to chemical energy through photosynthesis. In addition, light
is the principal means by which we are able to transmit and receive informa-
tion to and from objects around us and throughout the Universe.
The nature and properties of light have been a subject of great interest and spec-
ulation since ancient times. The Greeks believed that light consisted of tiny particles
(corpuscles) that were emitted by a light source and that these particles stimulated
the perception of vision upon striking the observer’s eye. Newton used this particle
theory to explain the reflection and refraction (bending) of light. In 1678, one of
Newton’s contemporaries, the Dutch scientist Christian Huygens, was able to explain
many other properties of light by proposing that light is a wave. In 1801, Thomas
Young showed that light beams can interfere with one another, giving strong support
to the wave theory. In 1865, Maxwell developed a brilliant theory that electromag-
netic waves travel with the speed of light (see Chapter 34). By this time, the wave
theory of light seemed to be firmly established.
However, at the beginning of the twentieth century, Max Planck returned to the
particle theory of light to explain the radiation emitted by hot objects. Einstein then
used the particle theory to explain how electrons are emitted by a metal exposed to
light. Today, scientists view light as having a dual nature—that is, light exhibits charac-
teristics of a wave in some situations and characteristics of a particle in other situa-
tions.
We shall discuss the particle nature of light in Part 6 of this text, which addresses
modern physics. In Chapters 35 through 38, we concentrate on those aspects
of light that are best understood through the wave model. First, we discuss the
reflection of light at the boundary between two media and the refraction that occurs
as light travels from one medium into another. Then, we use these ideas to study
reflection and refraction as light forms images due to mirrors and lenses. Next, we
describe how the lenses and mirrors used in such instruments as telescopes and
microscopes help us view objects not clearly visible to the naked eye. Finally,
we study the phenomena of diffraction, polarization, and interference as they apply
to light.
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P A R T
5
!
The Grand Tetons in western Wyoming are reflected in a smooth lake at sunset. The
optical principles that we study in this part of the book will explain the nature of the reflected
image of the mountains and why the sky appears red. (David Muench/CORBIS)
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