Light and Optics, Facts On File

Library of Congress Cataloging | English | ISBN-978-0-8160-6114-3 | June 2007 | PDF | 6.42 MB | 193 pages | RAR Compressed - 2.27 MB | No Password

Introduction
SEVERAL THOUSAND YEARS ago people believed that vision involved the emission of some kind of radiation by the eye. Everyone realized the eyes are necessary—an eye injury causes a loss of vision—but people in ancient times imagined the eye sent out rays and bounced them off distant objects, providing a sense of vision by analyzing the returning radiation. If vision really worked this way, then eyesight would result from the eye actively exploring the environment. But vision works differently. Arab scholar Abu Ali al-Hasan Ibn Al-Haitham (965–1040) correctly proposed that the eye receives radiation emitted by other sources; some of the radiation travels straight to the eye, which makes the source visible, and some of the radiation reaches the eye after bouncing off objects that do not otherwise emit radiation, which is how these objects become visible. The major source of this radiation, called light, is the Sun. Light is the messenger of vision, and the eye is tuned to detect it. The importance of light in
vision was an excellent motivator for scientists to study and experiment with this type of radiation, known as electromagnetic radiation. Optics is the study of light and the devices and instruments that make use of light. But visible light forms only a small portion of the broad range of radiation, and while the eye and instruments such as microscopes and telescopes are important topics, they do not by any means encompass the whole subject. Light and Optics adopts a physics perspective and explores the science of electromagnetic radiation and its tremendous variety of applications. The optics of image formation, described in chapter 2, is an essential aspect, but this volume also includes discussions of the intense beams of light produced by lasers, the role of light in biological processes such as photosynthesis and medical procedures such as laser surgery, astronomical observations based on all types of radiation, and applications involving communication, radar, and the transformation of light into electricity. An understanding of the science of light led to ways of correcting faulty vision, as well as the means of improving vision to study objects too small or too distant to be seen by the unaided eye. The performance of instruments such as microscopes, telescopes, and the human eye depends on the principles of optics. But even with these advances, some mysteries remain. The nature of light has puzzled scientists for centuries, and just when people think they have it figured out, light does something different. Sometimes light behaves as fields of energy oscillating—vibrating—at various rates, and sometimes light behaves as if it consists of a stream of small particles. These two behaviors are entirely different, yet both are within light’s amazing abilities. Whether future research will clear up this mystery or further deepen it is not presently known. Devices such as cell phones and X-ray machines employ electromagnetic radiation that is different from visible light in the number of oscillations per second; X-ray machines use radiation having a much higher oscillation rate than light, and cell phones use radiation having a lower rate. Although all the types of electromagnetic radiation share many of the same properties, the subtle differences are critical and lead to widely varying applications. The various types of electromagnetic radiation are also crucial in understanding the universe, which contains radiation emitters of almost every conceivable variety. Light has energy, and this energy is capable of extraordinary feats. The energy of sunlight is the basis of all life on Earth, for plants use it to make the food that feeds the world. When concentrated into a narrow laser beam, light can cut, burn, and even propel spaceships. People are just beginning to understand and appreciate the many things that the energy of light and other radiation can accomplish. Today’s equipment and technology are already impressive, and the future holds even more promise. Light and other types of radiation are even being used
today in the same way people used to think vision worked. Although the eye does not emit visual rays—that idea was wrong—there is nothing to stop people from building devices that do, and from sending out these rays to extend their vision to observe distant airplanes and detect drivers who exceed posted speed limits. The science and technology of light, radiation, and optics are full of ideas, old and new, to help people see farther and better, and in many strange and unique ways.

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