Chapter 5 Complete notes

Chapter 5 Complete notes - Electromagnetic Radiation...

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Electromagnetic Radiation (Light) At least 95% of the celestial information we receive is in the form of light. Because of this fact, astronomers have devised many techniques to decode as much as possible the messages that are encoded in the often extremely faint rays of light. These messages include information about the object's temperature, motion, chemical composition, gas density, surface gravity, shape, structure, and more! Roughly 85% of the information in light is uncovered by using spectroscopy ---spreading the light out into its different constituent colors or wavelengths and analyzing the spectrum. The first part of this chapter covers the characteristics of all forms of light and the following sections cover spectroscopic analysis. The vocabulary terms are in boldface . In order to understand light, you first need to have an understanding of electric fields and magnetic fields . Electrical charges and magnets alter the region of space around them so that they can exert forces on distant objects. This altered space is called a force field (or just a field ). Rather than describing the action of forces by having a distant object somehow reach out across space and push or pull on a body, the body simply responds to its local environment. An electric charge or a magnet responds to the field immediately surrounding it. That field is produced by a distant object. In the same way, a massive object can produce a gravity field that distant objects will respond to. Scientists have known since the early part of the 19th century that electrical fields and magnetic fields are intimately related to each other and applications of this connection are found all around you. Moving electric charge (electric current) creates a magnetic field. Coils of wire can be used to make the large electromagnets used in car junk yards or the tiny electromagnetics in your telephone receiver. Electric motors used to start your car or spin a computer's harddisk around are other applications of this phenomenon. In fact, ordinary magnets are produced from tiny currents at the atomic level. A changing magnetic field creates electrical current---an electric field. This concept is used by power generators---large coils of wire are made to turn in a magnetic field (by falling water, wind, or by steam from the heating of water by burning coal or oil or the heat from nuclear reactions). The coils of wire experience a changing magnetic field and electricity is produced. Computer disks and audio and video tapes encode information in magnetic patterns of alternating magnetic directions and magnetic strengths. When the magnetic disk or tape material passes by small coils of wire, electrical currents (electric fields) are produced. James Clerk Maxwell
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This note was uploaded on 05/24/2011 for the course PHYS 200 taught by Professor Touma during the Spring '11 term at Nebraska Wesleyan.

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Chapter 5 Complete notes - Electromagnetic Radiation...

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