Electromagnetic radiation is radiant energy having the properties of both particles and
waves. A continuum of different types of electromagnetic radiation—each type associated
with a particular energy range which constitutes the electromagnetic spectrum.
Visible light is the type of electromagnetic radiation with which we are most familiar, but
it represents only a fraction of the range of the entire electromagnetic spectrum.
X-rays and radio waves are other types of familiar electromagnetic radiation.
The electromagnetic spectrum is made up of the following components:
• Cosmic rays, which consist of radiation discharged by the sun, have the highest energy, the highest frequencies, and the shortest wavelengths.
• (gamma rays) are emitted from the nuclei of certain radioactive elements and, because of their high energy, can severely damage biological organisms.
• X-rays, somewhat lower in energy than are less harmful, except in high doses. Low-dose X-rays are used to examine the internal structure of organisms.
• Ultraviolet (UV) light is responsible for sunburns, and repeated exposure can cause skin cancer by damaging DNA molecules in skin cells.
• Visible light is the electromagnetic radiation we see.
• We feel infrared radiation as heat.
• We cook with microwaves and use them in radar.
• Radio waves have the lowest energy (lowest frequency). We use them for radio and television communication, digital imaging, remote controls, and wireless linkages for laptop computers. Radio waves are also used in NMR spectroscopy and in magnetic resonance imaging (MRI).
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