<text><span class="style10">lectro-magnetism</span><span class="style7"> </span><span class="style10">(5 of 5)THE ELECTROMAGNETIC SPECTRUM</span><span class="style7">Prior to Maxwell's discoveries it had been known that light was a wave motion, although the type of wave motion had not been identified. Maxwell was able to show that the oscillations were of the electric and magnetic field. Hertz's waves had a wavelength of about 60 cm; thus they were of much longer wavelength than light waves. Nowadays we recognize a spectrum of electromagnetic radiation that extends from about 10-15 m to 109 m. It is subdivided into smaller, sometimes overlapping, ranges. The extension of astronomical observations from visible to other electromagnetic wavelengths has revolutionized our knowledge of the universe.</span><span class="style26">Radio waves</span><span class="style7"> have a large range of wavelengths - from a few millimeters up to several kilometers.</span><span class="style26">Microwaves</span><span class="style7"> are radio waves with shorter wavelengths, between 1 mm and 30 cm. They are used in radar and microwave ovens.</span><span class="style26">Infrared waves </span><span class="style7">of different wavelengths are radiated by bodies at different temperatures. (Bodies at higher temperatures radiate either visible or ultraviolet waves.) The Earth and its atmosphere, at a mean temperature of 250 K (-23 deg C or -9.4 deg F) radiates infrared waves with wavelengths centered at about 10 micrometers ( m) or 10-5 m (1 m = 10-6 m).</span><span class="style26">Visible waves</span><span class="style7"> have wavelengths of 400-700 manometers (nm; 1 nm = 10-9 m). The peak of the solar radiation (temperature of about 6000 K / 6270 deg C / 11 323 deg F) is at a wavelength of about 550 nm, where the human eye is at its most sensitive. </span><span class="style26">Ultraviolet</span><span class="style7"> </span><span class="style26">waves </span><span class="style7">have wavelengths from about 380 nm down to 60 nm. The radiation from hotter stars (above 25 000 K / 25 000 deg C / 45 000 deg F is shifted towards the violet and ultraviolet parts of the spectrum. </span><span class="style26">X-rays</span><span class="style7"> have wavelengths from about 10 nm down to 10-4 nm.</span><span class="style26">Gamma rays</span><span class="style7"> have wavelengths less than 10-11 m. They are emitted by certain radio active nuclei and in the course of some nuclear reactions.Note that the cosmic rays continually bombarding the Earth from outer space are not electromagnetic waves, but high-speed protons and x-particles (i.e. nuclei of hydrogen and helium atoms) together with some heavier nuclei.</span></text>
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<id>23</id>
<text>ΓÇó STARS AND GALAXIESΓÇó QUANTUM THEORY AND RELATIVITYΓÇó WAVE THEORYΓÇó OPTICSΓÇó ELECTRICITY IN ACTIONΓÇó ATOMS AND SUBATOMIC PARTICLESΓÇó THE EARTH'S STRUCTUREΓÇó MEDICAL TECHNOLOGYΓÇó RADIO, TELEVISION AND VIDEOΓÇó SEEING THE INVISIBLE</text>
