2005/07/17 | 电磁辐射[Electromagnetic Radiation]
类别(Ω〖物理〗) | 评论(0) | 阅读(58) | 发表于 08:58
<P>

The radiation of energy as transverse waves that is produced by moving charges. A charge can radiate electromagnetic
radiation only if it is undergoing accelerated motion. There is one exception: a charge moving at a constant velocity
through a dielectric can emit <a href="CherenkovRadiation.html">Cherenkov radiation</a>. Electromagnetic radiation is also known as an electromagnetic
wave, and consists of oscillating electric and magnetic fields at right angles to one another and to the propagation
direction. Electromagnetic radiation comes in discrete packets known as <a href="Photon.html">photons</a>.

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In a vacuum, electromagnetic radiation prorogates at the <a href="SpeedofLight.html">speed of light</a> <i>c</i>, and at a speed
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in matter, where <i>n</i> is the <a href="IndexofRefraction.html">index of refraction</a> of the given material. Electromagnetic radiation has a
characteristic <a href="Wavelength.html">wavelength</a> <IMG
WIDTH="13" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="http://scienceworld.wolfram.com/physics/eimg343.gif"> (and <a href="Frequency.html">frequency</a> <IMG
WIDTH="13" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="http://scienceworld.wolfram.com/physics/eimg240.gif">), with the two related by <div ALIGN="CENTER">



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The following table summarizes the names given to electromagnetic radiation based on its <a href="Wavelength.html">wavelength</a>.

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<TABLE CELLPADDING=3 BORDER="1">
<TR><TD ALIGN="LEFT">wavelength range</TD>
<TD ALIGN="LEFT">name</TD>
</TR>
<TR><TD ALIGN="LEFT">1 cm</TD>
<TD ALIGN="LEFT"><a href="Microwave.html">microwave</a></TD>
</TR>
<TR><TD ALIGN="LEFT">1 mm-10 <IMG
WIDTH="14" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="http://scienceworld.wolfram.com/physics/eimg321.gif">m</TD> <TD ALIGN="LEFT"><a href="Infrared.html">infrared</a></TD>
</TR>
<TR><TD ALIGN="LEFT">0.1 mm-1 mm</TD>
<TD ALIGN="LEFT"><a href="Submillimeter.html">submillimeter</a></TD>
</TR>
<TR><TD ALIGN="LEFT">1 <IMG
WIDTH="14" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="http://scienceworld.wolfram.com/physics/eimg321.gif">m</TD> <TD ALIGN="LEFT"><a href="NearInfrared.html">near infrared</a></TD>
</TR>
<TR><TD ALIGN="LEFT">400-750 nm</TD>
<TD ALIGN="LEFT"><a href="VisibleLight.html">visible light</a></TD>
</TR>
<TR><TD ALIGN="LEFT">100-10 nm</TD>
<TD ALIGN="LEFT"><a href="Ultraviolet.html">ultraviolet</a></TD>
</TR>
<TR><TD ALIGN="LEFT"><IMG
WIDTH="37" HEIGHT="28" ALIGN="MIDDLE" BORDER="0"
SRC="http://scienceworld.wolfram.com/physics/eimg766.gif"> nm</TD>
<TD ALIGN="LEFT"><a href="X-Ray.html">X-ray</a></TD>
</TR>
<TR><TD ALIGN="LEFT">&nbsp;</TD>
<TD ALIGN="LEFT"><a href="GammaRay.html">gamma ray</a></TD>
</TR>
</TABLE>
</DIV>
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