http://www.ck12.org Chapter 21. Electromagnetic Radiation
CHAPTER
21 Electromagnetic Radiation
Chapter Outline
21.1 Electromagnetic Waves
21.2 PROPERTIES OFELECTROMAGNETICWAVES
21.3 THEELECTROMAGNETICSPECTRUM
21.4 REFERENCES
Why is this picture of a cat so colorful? No cat looks like this to the human eye. The picture was taken with a special
camera that senses infrared light. This is a form of energy given off by warm objects. Areas that appear yellow are
the warmest, and areas that appear purple are the coolest. The picture shows that the cat’s eyes are the warmest part
of its head. Why can’t people see images like this without a camera? The answer has to do with the wavelengths of
infrared light. Its wavelengths are too long for the human eye to detect. In fact, the human eye can detect light only
in a very narrow range of wavelengths, called visible light. You’ll learn more about infrared light, visible light, and
other forms of electromagnetic radiation in this chapter.
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